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  • 1. Bahr, Adam
    et al.
    Ellström, Magnus
    Akselsson, Cecilia
    Ekblad, Alf
    Örebro University, School of Science and Technology.
    Mikusinska, Anna
    Örebro University, School of Science and Technology.
    Wallander, Håkan
    Growth of ectomycorrhizal fungal mycelium along a Norway spruce forest nitrogen deposition gradient and its effect on nitrogen leakage2013In: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 59, p. 38-48Article in journal (Refereed)
    Abstract [en]

    Almost all boreal and temperate forest tree species live in symbiosis with ectomycorrhizal fungi (EMF); the trees transfer carbon (C) to the fungi in exchange for nutrients and water. Several studies have shown that experimental application of inorganic nitrogen (N) represses production of EMF extramatrical mycelia (EMM), but studies along N deposition gradients are underrepresented. Other environmental variables than N may influence EMM production and in this study we included 29 thoroughly monitored Norway spruce stands from a large geographical region in Sweden in order to evaluate the importance of N deposition on EMM growth and N leaching in a broader context. It was concluded that N deposition was the most important factor controlling EMM production and that the amounts typically deposited in boreal and boreo-nemoral regions can be sufficient to reduce EMM growth. Other factors, such as phosphorus status and pH, were also correlated with EMM production and should be considered when predicting EMM growth and N leaching. We also showed that EMM production substantially contributed to the C sequestration (320 kg ha(-1) yr(-1)), suggesting that it should be included in C cycle modelling. Furthermore, EMF are probably important for the N retention capacity since high N leaching coincided with low EMM growth. However, it was not possible to differentiate between the effects of EMF and the direct effect of N deposition on N leaching in the present study.

  • 2. Berglund, S. Linnea
    et al.
    Agren, Goran I.
    Ekblad, Alf
    Örebro University, School of Science and Technology.
    Carbon and nitrogen transfer in leaf litter mixtures2013In: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 57, p. 341-348Article in journal (Refereed)
    Abstract [en]

    The decomposition rate of litter mixtures can differ from that expected on the basis of the decomposition rate of the individual components. This difference may be linked to nitrogen (N) transfer from high-N to low-N components. Transfer of N is probably also associated with transfer of C, but the extent and direction of this C transfer are unknown. This study examined transfer and loss in laboratory microcosms of C and N from two mixed litter species (Scots pine, Pinus sylvestris L and maize, Zea mays L), which have natural isotopic differences in C-13. Half the material was N-15-labelled and the plants were fertilised or unfertilised. Substantial bidirectional transfer of C and N occurred between the litters, with net transfer of C from pine to maize litter and net transfer of N from high-N to low-N litter. Mixtures of fertilised and unfertilised plant litter showed higher than expected C losses and net transfer of N. Mixtures with litters from the same fertilisation treatment had small or insignificant net transfer of N and their C losses did not differ from values estimated using the decomposition rates of the pure litters.

  • 3.
    Boberg, Johanna B.
    et al.
    Uppsala BioCtr, Dept Forest Mycol & Plant Pathol, Swedish Univ Agr Sci, Uppsala, Sweden.
    Finlay, Roger D.
    Uppsala BioCtr, Dept Forest Mycol & Plant Pathol, Swedish Univ Agr Sci, Uppsala, Sweden.
    Stenlid, Jan
    Uppsala BioCtr, Dept Forest Mycol & Plant Pathol, Swedish Univ Agr Sci, Uppsala, Sweden.
    Ekblad, Alf
    Örebro University, School of Science and Technology.
    Lindahl, Björn D.
    Uppsala BioCtr, Dept Forest Mycol & Plant Pathol, Swedish Univ Agr Sci, Uppsala, Sweden.
    Nitrogen and Carbon Reallocation in Fungal Mycelia during Decomposition of Boreal Forest Litter2014In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 9, no 3, p. e92897-Article in journal (Refereed)
    Abstract [en]

    Boreal forests are characterized by spatially heterogeneous soils with low N availability. The decomposition of coniferous litter in these systems is primarily performed by basidiomycete fungi, which often form large mycelia with a well-developed capacity to reallocate resources spatially-an advantageous trait in heterogeneous environments. In axenic microcosm systems we tested whether fungi increase their biomass production by reallocating N between Pinus sylvestris (Scots pine) needles at different stages of decomposition. We estimated fungal biomass production by analysing the accumulation of the fungal cell wall compound chitin. Monospecific systems were compared with systems with interspecific interactions. We found that the fungi reallocated assimilated N and mycelial growth away from well-degraded litter towards fresh litter components. This redistribution was accompanied by reduced decomposition of older litter. Interconnection of substrates increased over-all fungal C use efficiency (i.e. the allocation of assimilated C to biomass rather than respiration), presumably by enabling fungal translocation of growth-limiting N to litter with higher C quality. Fungal connection between different substrates also restricted N-mineralization and production of dissolved organic N, suggesting that litter saprotrophs in boreal forest ecosystems primarily act to redistribute rather than release N. This spatial integration of different resource qualities was hindered by interspecific interactions, in which litters of contrasting quality were colonised by two different basidiomycete species. The experiments provide a detailed picture of how resource reallocation in two decomposer fungi leads to a more efficient utilisation of spatially separated resources under N-limitation. From an ecosystem point of view, such economic fungal behaviour could potentially contribute to organic matter accumulation in the litter layers of boreal forests.

  • 4.
    Boström, Björn
    et al.
    Örebro University, Department of Natural Sciences.
    Comstedt, Daniel
    Örebro University, Department of Natural Sciences.
    Ekblad, Alf
    Örebro University, Department of Natural Sciences.
    Can isotopic fractionation during respiration explain the 13C-enriched sporocarps of ectomycorrhizal and saprotrophic fungi?2008In: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 177, no 4, p. 1012-1019Article in journal (Refereed)
    Abstract [en]

    • The mechanism behind the 13C enrichment of fungi relative to plant materials is unclear and constrains the use of stable isotopes in studies of the carbon cycle in soils.

    • Here, we examined whether isotopic fractionation during respiration contributes to this pattern by comparing δ13C signatures of respired CO2, sporocarps and their associated plant materials, from 16 species of ectomycorrhizal or saprotrophic fungi collected in a Norway spruce forest.

    • The isotopic composition of respired CO2 and sporocarps was positively correlated. The differences in δ13C between CO2 and sporocarps were generally small, < ±1‰ in nine out of 16 species, and the average shift for all investigated species was 0.04‰. However, when fungal groups were analysed separately, three out of six species of ectomycorrhizal basidiomycetes respired 13C-enriched CO2 (up to 1.6‰), whereas three out of five species of polypores respired 13C-depleted CO2 (up to 1.7‰; P < 0.05). The CO2 and sporocarps were always 13C-enriched compared with wood, litter or roots.

    • Loss of 13C-depleted CO2 may have enriched some species in 13C. However, that the CO2 was consistently 13C-enriched compared with plant materials implies that other processes must be found to explain the consistent 13C-enrichment of fungal biomass compared with plant materials.

  • 5.
    Boström, Björn
    et al.
    Örebro University, Department of Natural Sciences.
    Comstedt, Daniel
    Örebro University, Department of Natural Sciences.
    Ekblad, Alf
    Örebro University, Department of Natural Sciences.
    Isotope fractionation and 13C enrichment in soil profiles during the decomposition of soil organic matter2007In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 153, no 1, p. 89-98Article in journal (Refereed)
    Abstract [en]

    The mechanisms behind the 13C enrichment of organic matter with increasing soil depth in forests are unclear. To determine if 13C discrimination during respiration could contribute to this pattern, we compared d13C signatures of respired CO2 from sieved mineral soil, litter layer and litterfall with measurements of d13C and d15N of mineral soil, litter layer, litterfall, roots and fungal mycelia sampled from a 68-year-old Norway spruce forest stand planted on previously cultivated land. Because the land was subjected to ploughing before establishment of the forest stand, shifts in d13C in the top 20 cm reflect processes that have been active since the beginning of the reforestation process. As 13C-depleted organic matter accumulated in the upper soil, a 1.0 o/oo d13C gradient from –28.5 o/oo in the litter layer to –27.6 o/oo at a depth of 2–6 cm was formed. This can be explained by the 1 o/oo drop in d13C of atmospheric CO2 since the beginning of reforestation together with the mixing of new C (forest) and old C (farmland). However, the isotopic change of the atmospheric CO2 explains only a portion of the additional 1.0& increase in d13C below a depth of 20 cm. The d13C of the respired CO2 was similar to that of the organic matter in the upper soil layers but became increasingly 13C enriched with depth, up to 2.5 o/oo relative to the organic matter. We hypothesise that this 13C enrichment of the CO2 as well as the residual increase in d13C of the organic matter below a soil depth of 20 cm results from the increased contribution of 13C-enriched microbially derived C with depth. Our results suggest that 13C discrimination during microbial respiration does not contribute to the 13C enrichment of organic matter in soils. We therefore recommend that these results should be taken into consideration when natural variations in d13C of respired CO2 are used to separate different components of soil respiration or ecosystem respiration.

  • 6.
    Boström, Björn
    et al.
    Örebro University, Department of Natural Sciences.
    Ekblad, Alf
    Örebro University, Department of Natural Sciences.
    Gleixner, Gerd
    Hettmann, Elena
    Volders, Filip
    Carbon isotope ratios in ectomycorrhizal and saprotrophic metabolites in relation to the δ13C of substrate, sporocarps and respired CO2 Manuscript (preprint) (Other academic)
  • 7. Clemmensen, K. E.
    et al.
    Bahr, A.
    Ovaskainen, O.
    Dahlberg, A.
    Ekblad, Alf
    Örebro University, School of Science and Technology.
    Wallander, H.
    Stenlid, J.
    Finlay, R. D.
    Wardle, D. A.
    Lindahl, B. D.
    Roots and associated fungi drive long-term carbon sequestration in boreal forest2013In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 339, no 6127, p. 1615-1618Article in journal (Refereed)
    Abstract [en]

    Boreal forest soils function as a terrestrial net sink in the global carbon cycle. The prevailing dogma has focused on aboveground plant litter as a principal source of soil organic matter. Using C-14 bomb-carbon modeling, we show that 50 to 70% of stored carbon in a chronosequence of boreal forested islands derives from roots and root-associated microorganisms. Fungal biomarkers indicate impaired degradation and preservation of fungal residues in late successional forests. Furthermore, 454 pyrosequencing of molecular barcodes, in conjunction with stable isotope analyses, highlights root-associated fungi as important regulators of ecosystem carbon dynamics. Our results suggest an alternative mechanism for the accumulation of organic matter in boreal forests during succession in the long-term absence of disturbance.

  • 8.
    Comstedt, Daniel
    et al.
    Örebro University, Department of Natural Sciences.
    Boström, Björn
    Örebro University, Department of Natural Sciences.
    Ekblad, Alf
    Örebro University, Department of Natural Sciences.
    Autotrophic and heterotrophic soil respiration in a Norway spruce forest: estimating the root decomposition and soil moisture effects in a trenching experimentManuscript (Other academic)
  • 9.
    Comstedt, Daniel
    et al.
    Örebro University, School of Science and Technology.
    Boström, Björn
    Örebro University, School of Science and Technology.
    Ekblad, Alf
    Örebro University, School of Science and Technology.
    Autotrophic and heterotrophic soil respiration in a Norway spruce forest: estimating the root decomposition and soil moisture effects in a trenching experiment2011In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 104, no 1-3, p. 121-132Article in journal (Refereed)
    Abstract [en]

    The two components of soil respiration, autotrophic respiration (from roots, mycorrhizal hyphae and associated microbes) and heterotrophic respiration (from decomposers), was separated in a root trenching experiment in a Norway spruce forest. In June 2003, cylinders (29.7 cm diameter) were inserted to 50 cm soil depth and respiration was measured both outside (control) and inside the trenched areas. The potential problems associated with the trenching treatment, increased decomposition of roots and ectomycorrhizal mycelia and changed soil moisture conditions, were handled by empirical modelling. The model was calibrated with respiration, moisture and temperature data of 2004 from the trenched plots as a training set. We estimate that over the first 5 months after the trenching, 45% of respiration from the trenched plots was an artefact of the treatment. Of this, 29% was a water difference effect and 16% resulted from root and mycelia decomposition. Autotrophic and heterotrophic respiration contributed to about 50% each of total soil respiration in the control plots averaged over the two growing seasons. We show that the potential problems with the trenching, decomposing roots and mycelia and soil moisture effects, can be handled by a modelling approach, which is an alternative to the sequential root harvesting technique.

  • 10.
    Comstedt, Daniel
    et al.
    Örebro University, Department of Natural Sciences.
    Boström, Björn
    Marshall, John
    Holm, Anders
    Slaney, Michelle
    Linder, Sune
    Ekblad, Alf
    Effects of elevated atmospheric carbon dioxide and temperature on soil respiration in a boreal forest using δ13C as a labeling tool2006In: Ecosystems (New York. Print), ISSN 1432-9840, E-ISSN 1435-0629, Vol. 9, no 8, p. 1266-1277Article in journal (Refereed)
  • 11.
    Comstedt, Daniel
    et al.
    Örebro University, Department of Natural Sciences.
    Boström, Björn
    Thompson, Matthew V.
    Ekblad, Alf
    A link between above ground weather conditions and the δ13C of forest soil respiration is not always observedManuscript (Other academic)
  • 12.
    Dawes, Melissa A.
    et al.
    Mountain Ecosystems, WSL Institute for Snow and Avalanche Research-SLF, Davos Dorf, Switzerland .
    Hagedorn, Frank
    Forest Soils and Biogeochemistry, Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Birmensdorf, Switzerland .
    Handa, Ira Tanya
    Université du Québec à Montréal (UQÀM), Montreal, Canada .
    Streit, Kathrin
    Paul Scherrer Institute, Villigen, Switzerland .
    Ekblad, Alf
    Örebro University, School of Science and Technology.
    Rixen, Christian
    Mountain Ecosystems, WSL Institute for Snow and Avalanche Research-SLF, Davos Dorf, Switzerland .
    Körner, Christian
    University of Basel, Basel, Switzerland .
    Hättenschwiler, Stephan
    Centre d’Ecologie Fonctionnelle et Evolutive (CEFE), Montpellier, France.
    An alpine treeline in a carbon dioxide-rich world: synthesis of a nine-year free-air carbon dioxide enrichment study2013In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 171, no 3, p. 623-637Article in journal (Refereed)
    Abstract [en]

    We evaluated the impacts of elevated CO2 in a treeline ecosystem in the Swiss Alps in a 9-year free-air CO2 enrichment (FACE) study. We present new data and synthesize plant and soil results from the entire experimental period. Light-saturated photosynthesis (A max) of ca. 35-year-old Larix decidua and Pinus uncinata was stimulated by elevated CO2 throughout the experiment. Slight down-regulation of photosynthesis in Pinus was consistent with starch accumulation in needle tissue. Above-ground growth responses differed between tree species, with a 33 % mean annual stimulation in Larix but no response in Pinus. Species-specific CO2 responses also occurred for abundant dwarf shrub species in the understorey, where Vaccinium myrtillus showed a sustained shoot growth enhancement (+11 %) that was not apparent for Vaccinium gaultherioides or Empetrum hermaphroditum. Below ground, CO2 enrichment did not stimulate fine root or mycorrhizal mycelium growth, but increased CO2 effluxes from the soil (+24 %) indicated that enhanced C assimilation was partially offset by greater respiratory losses. The dissolved organic C (DOC) concentration in soil solutions was consistently higher under elevated CO2 (+14 %), suggesting accelerated soil organic matter turnover. CO2 enrichment hardly affected the C–N balance in plants and soil, with unaltered soil total or mineral N concentrations and little impact on plant leaf N concentration or the stable N isotope ratio. Sustained differences in plant species growth responses suggest future shifts in species composition with atmospheric change. Consistently increased C fixation, soil respiration and DOC production over 9 years of CO2 enrichment provide clear evidence for accelerated C cycling with no apparent consequences on the N cycle in this treeline ecosystem.

  • 13.
    Deckmyn, G.
    et al.
    Univ Antwerp, Antwerp, Belgium.
    Meyer, A.
    Dept Biol & Environm Sci, Univ Gothenburg, Gothenburg, Sweden.
    Smits, M. M.
    Ctr Environm Sci, Hasselt Univ, Diepenbeek, Belgium.
    Ekblad, Alf
    Örebro University, School of Science and Technology.
    Grebenc, T.
    Slovenian Forestry Inst, Ljubljana, Slovenia.
    Komarov, A.
    Inst Physicochem & Biol Problems Soil Sci, Pushchino, Russian Academy of Science, Moscow Region, Russia.
    Kraigher, H.
    Slovenian Forestry Inst, Ljubljana, Slovenia.
    Simulating ectomycorrhizal fungi and their role in carbon and nitrogen cycling in forest ecosystems2014In: Canadian Journal of Forest Research, ISSN 0045-5067, E-ISSN 1208-6037, Vol. 44, no 6, p. 535-553Article, review/survey (Refereed)
    Abstract [en]

    Although ectomycorrhizal fungi play an important role in forest ecosystem functioning, they are usually not included in forest growth or ecosystem models. Simulation is hampered by two main issues: a lack of understanding of the ecological functioning of the ectomycorrhizal fungi and a lack of adequate basic data for parameterization and validation. Concerning these issues, much progress has been made during the past few years, but this information has not found its way into the forest and soil models. In this paper, state-of-the-art insight into ectomycorrhizal functioning and basic values are described in a manner transparent to nonspecialists and modelers, together with the existing models and model strategies. As such, this paper can be the starting point and the motivator to include ectomycorrhizal fungi into existing soil and forest ecosystem models.

  • 14.
    Ekblad, Alf
    et al.
    Örebro University, Department of Natural Sciences.
    Boström, Björn
    Örebro University, Department of Natural Sciences.
    Holm, Anders
    Örebro University, Department of Natural Sciences.
    Comstedt, Daniel
    Örebro University, Department of Natural Sciences.
    Forest soil respiration rate and d13C is regulated by recent above ground weather conditions2005In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 143, no 1, p. 136-142Article in journal (Refereed)
    Abstract [en]

    Soil respiration, a key component of the global carbon cycle, is a major source of uncertainty when estimating terrestrial carbon budgets at ecosystem and higher levels. Rates of soil and root respiration are assumed to be dependent on soil temperature and soil moisture yet these factors often barely explain half the seasonal variation in soil respiration. We here found that soil moisture (range 16.5-27.6% of dry weight) and soil temperature (range 8-17.5 degrees C) together explained 55% of the variance (cross-validated explained variance; Q2) in soil respiration rate (range 1.0-3.4 micromol C m(-2) s(-1)) in a Norway spruce (Picea abies) forest. We hypothesised that this was due to that the two components of soil respiration, root respiration and decomposition, are governed by different factors. We therefore applied PLS (partial least squares regression) multivariate modelling in which we, together with below ground temperature and soil moisture, used the recent above ground air temperature and air humidity (vapour pressure deficit, VPD) conditions as x-variables. We found that air temperature and VPD data collected 1-4 days before respiration measurements explained 86% of the seasonal variation in the rate of soil respiration. The addition of soil moisture and soil temperature to the PLS-models increased the Q2 to 93%. delta13C analysis of soil respiration supported the hypotheses that there was a fast flux of photosynthates to root respiration and a dependence on recent above ground weather conditions. Taken together, our results suggest that shoot activities the preceding 1-6 days influence, to a large degree, the rate of root and soil respiration. We propose this above ground influence on soil respiration to be proportionally largest in the middle of the growing season and in situations when there is large day-to-day shifts in the above ground weather conditions. During such conditions soil temperature may not exert the major control on root respiration.

  • 15.
    Ekblad, Alf
    et al.
    Örebro University, School of Science and Technology.
    Godbold, Douglas L.
    Wallander, Håkan
    The ectomycorrhizal mycelium and its importance in carbon cycling: strengths and weaknesses in current knowledge2010In: Below ground carbon turnover in European forests: state of the art / [ed] Ivano Brunner, Birmensdorf: Swiss Federal Institute for Forest, Snow and Landscape Research WSL , 2010, p. 23-30Conference paper (Refereed)
    Abstract [en]

    The ecological importance of the extramatrical (EM) mycelia of mycorrhizal fungi is immense. To list but a few key functions; they are essential for nutrient uptake, growth and survival of most land plants. They are important for plant-plant interactions and for food webs in the soil. The production of the EM mycelium of ectomycorrhizas in forests might be in the same range as that of the fine roots. Thus the amount of carbon invested in the construction, operation and maintenance of this system is potentially very large. The importance of the EM mycelium in carbon cycling in ecosystems has only recently been recognised by a broader scientific community. However, currently our knowledge is limited of the basic parameters needed to calculate the extent of the EM mycelium in C dynamics such as variation in mycelial production, standing biomass and thus turnover rates, as well as its importance for the formation of stable soil carbon. Further, we also know very little about the regulating mechanisms behind such variations. In this paper we will first make a brief review of the current knowledge of the EM mycelium in C soil dynamics and identify important gaps in this knowledge. We will then present the methods currently available to estimate mycelial production and standing biomass, and subsequently turnover, and discuss their strengths and weaknesses.

  • 16.
    Ekblad, Alf
    et al.
    Umeå universitet, Umeå, Sweden.
    Huss-Danell, K.
    Sjöström, M.
    Variation in nitrogenase activity explained by abiotic and biotic factors: a multivariate study1990In: Physiologia Plantarum: An International Journal for Plant Biology, ISSN 0031-9317, E-ISSN 1399-3054, Vol. 79, no 2, p. A77-A77Article in journal (Other academic)
  • 17.
    Ekblad, Alf
    et al.
    Swedish University of Agricultural Sciences, Umeå, Sweden.
    Huss-Danell, Kerstin
    Swedish University of Agricultural Sciences, Umeå, Sweden.
    Nitrogen fixation by Alnus incana and nitrogen transfer from A-incana to Pinus sylvestris influenced by macronutrients and ectomycorrhiza1995In: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 131, no 4, p. 453-459Article in journal (Refereed)
    Abstract [en]

    The aims of this study were to evaluate the effect of macronutrients on nitrogen fixation in mycorrhizal and non-mycorrhizal grey alder (Alnus incana (L.) Moench), and to evaluate the effect of ectomycorrhizal mycelium on the transfer of symbolically fixed nitrogen from grey alder to Scots pine (Pinus sylvestris L). One alder and one pine were grown together in pots with root systems separated by a 20μm mesh nylon filter which allowed hyphae but not roots to penetrate. Half the plants of both species were inoculated with Paxillus involutus (Ft.) Ft. and all alders were inoculated with Frankia. Nutrient solutions were added with macronutrient (N, K, P, Ca, Mg and S) concentrations varied according to a two-level fractional factorial design. The plants were harvested after two growing periods in a growth chamber. Nitrogen fixation by alder and transfer of symbiotically fixed N from alder to pine was measured by 15N-dilution. Fixed N (mg) correlated with nodule biomass in both mycorrhizal and non-mycorrhizal alders. On average, specific nodule activity over the two periods was 510 mg N fixed R' nodule d. wt. This was not affected by mycorrhizal infection or by the different nutrient treatments. By contrast there was a strong nutrient effect on the proportion of N derived from fixation. These results indicate that the regulation of nitrogen fixation was via nodule growth rather than via nodule specific activity. Nitrogen had a strong negative effect and P a positive effect on the percentage of N derived from fixation (%Ndfa). However, the effect of N depended on the level of P. This N × P interaction resulted in a %Ndfa when N was high, of 5-10%, at low P and 45–48%, at high P. The highest value of 90% Ndfa was found at the combination of low N and high P. Potassium had a small but statistically significant effect on the %Ndfa but Ca, Mg and S had no significant effects. No mycorrhizal effect was found on the %Ndfa in alder. By contrast, the %Ndfa and biomass were lower in mycorrhizal than in non-mycorrhizal alders. The proportion of fixed N in pine, transferred from alder, was greatest (9%) when the pine was nitrogen starved and mycorrhizal and the alder was fixing maximally (low N and high P). However, the amount of fixed N transferred to pine was not statistically different from zero.

  • 18.
    Ekblad, Alf
    et al.
    Swedish University of Agricultural Sciences, Umeå, Sweden.
    Högberg, Peter
    Swedish University of Agricultural Sciences, Umeå, Sweden.
    Analysis of delta C-13 of CO2 distinguishes between microbial respiration of added C-4-sucrose and other soil respiration in a C-3-ecosystem2000In: Plant and Soil, ISSN 0032-079X, E-ISSN 1573-5036, Vol. 219, no 1-2, p. 197-209Article in journal (Refereed)
    Abstract [en]

    The main aim of this study was to test various hypotheses regarding the changes in δ13C of emitted CO2 that follow the addition of C4-sucrose to the soil of a C3-ecosystem. It forms part of an experimental series designed to assess whether or not the contributions from C3-respiration (root and microbial) and C4-respiration (microbial) to total soil respiration can be calculated from such changes. A series of five experiments, three on sieved (root-free) mor-layer material, and two in the field with intact mor-layer (and consequently with active roots), were performed. Both in the experiments on sieved mor-layer and the field experiments, we found a C4-sucrose-induced increase in C3-respiration that accounted for between 30% and 40% of the respiration increase 1 h after sucrose addition. When the course of C3-, C4- and total respiration was followed in sieved material over four days following addition of C4-sucrose, the initially increased respiration of C3-C was transient, passing within less than 24 h. In a separate pot experiment, neither ectomycorrhizal Pinus sylvestrisL. roots nor non-mycorrhizal roots of this species showed respiratory changes in response to exogenous sucrose. No shift in the δ13C of the evolved CO2 after adding C3-sucrose to sieved mor-layer material was found, confirming that the sucrose-induced increase in respiration of endogenous C was not an artefact of discrimination against 13C during respiration. Furthermore, we conclude that the C4-sucrose induced transient increase in C3-respiration is most likely the result of accelerated turnover of C in the microbial biomass. Thus, neither respiration of mycorrhizal roots, nor processes discriminating against δ13C were likely sources of error in the field. The estimated δ13C of evolved soil CO2 in three field experiments lay between −25.2‰ and −23.6‰. The study shows that we can distinguish between CO2 evolved from microbial mineralisation of added C4-sucrose, and CO2 evolved from endogenous carbon sources (roots and microbial respiration).

  • 19.
    Ekblad, Alf
    et al.
    Örebro University, School of Science and Technology. Swedish University of Agricultural Sciences, Umeå, Sweden.
    Högberg, Peter
    Swedish University of Agricultural Sciences, Umeå, Sweden.
    Natural abundance of C-13 in CO2 respired from forest soils reveals speed of link between tree photosynthesis and root respiration2001In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 127, no 3, p. 305-308Article in journal (Refereed)
    Abstract [en]

    Soil respiration from a boreal mixed coniferous forest showed large seasonal variation in natural abundance of 13C, ranging from –21.6‰ to –26.5‰. We tested if weather conditions could explain this variation in δ13C of respired CO2, and found that the air relative humidity 1–4 days before the days of CO2 sampling best explained the variation. This suggested that high δ13C values were caused by effects of air humidity on isotope fractionation during photosynthesis and that it took 1–4 days for the C from canopy photosynthesis of 20–25 m trees to become available for root/rhizosphere respiration. We calculated that these new photoassimilates could account for at least 65% of total soil respiration.

  • 20.
    Ekblad, Alf
    et al.
    Umeå University, Umeå, Sweden.
    Lundquist, Per-Olof
    Sjöström, M
    Umeå University, Umeå, Sweden.
    Huss-Danell, Kerstin
    Umeå University, Umeå, Sweden.
    Day-to-day variation in nitrogenase activity of alnus-incana explained by weather variables: a multivariate time-series analysis1994In: Plant, Cell and Environment, ISSN 0140-7791, E-ISSN 1365-3040, Vol. 17, no 3, p. 319-325Article in journal (Refereed)
    Abstract [en]

    A modelling system is described that indicates the extent to which day-to-day variations in nitrogenase activity in young Alnus incana (L.) Moench, grown in defined conditions in the field, may be affected by weather conditions both during and prior to the day of measurement. Nitrogenase activity (acetylene reduction activity, ARA) was measured weekly on intact field-grown grey alder (A. incana) plants, 0.15–0.42 m tall at planting, nodulated with Frankia. The measurements were done at noon on two groups of plants in 1987 and on two other groups in 1988. Each group was made up of five or six plants. Seven weather variables: daily sunshine hours, daily mean, maximum and minimum air temperature, daily mean and 1300 h relative humidity, and daily rainfall were used. The relation between log(ARA/leaf area) and the weather variables were analysed using a PLS model (partial least squares projection to latent structures). The advantage of PLS is that it can handle x-variables that are correlated. Data from 1987 were chosen as a training set. Multivariate PLS time series analysis was made by adding, in a stepwise manner, the weather data up to 5 d before the day of measurement. This procedure gave six models with n * 7 x-variables (n= 1–6). With the models from the time series analysis of 1987 data, true predictions of ARA per leaf area were made from weather data 1988 (test set 1) and from ‘early-season’ weather data from 1987 and 1988 (test set 2). The variation in ARA/leaf area could be predicted from the weather conditions. The predictions of the two test sets improved when the weather conditions one and two days before the day of measurements were added to the model. The further addition of weather data from 3 to 5 d before the day of measurement did not improve the model. The good predictions of ARA/leaf area show that the alders responded to the variable weather conditions in the same way in 1988 as in 1987, despite the ten-fold difference in size (leaf area) at the end of the growing season. Among the weather variables, air temperature and the daily sunshine hours were positively correlated to ARA, while relative air humidity and rainfall were negatively correlated to ARA. The daily minimum temperature and rainfall appeared to have least impact on ARA. By use of PLS, we could extract information out of a data set containing highly correlated x-variables, information that is non-accessible with conventional statistical tools such as multiple regression. When making measurements of nitrogenase activities under field conditions, we propose that attention should be paid to the weather conditions on the days preceding the day of measurement. The day-to-day variation in nitrogenase activity is discussed with reference to known effects of stress factors under controlled conditions.

  • 21.
    Ekblad, Alf
    et al.
    Örebro University, School of Science and Technology.
    Mikusinska, Anna
    School of Science & Technology, Örebro University, Örebro, Sweden.
    Ågren, Göran I.
    Department of Ecology, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Menichetti, Lorenzo
    Agroscope, Zürich, Switzerland.
    Wallander, Håkan
    Department of Biology, Microbial Ecology, Lund University, Lund, Sweden.
    Vilgalys, Rytas
    Nicholas School of the Environment, Duke University, Durham, USA.
    Bahr, Adam
    Department of Biology, Microbial Ecology, Lund University, Lund, Sweden.
    Eriksson, Ulrika
    Örebro University, School of Science and Technology.
    Production and turnover of ectomycorrhizal extramatrical mycelial biomass and necromass under elevated CO2 and nitrogen fertilization2016In: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 211, no 3, p. 874-885Article in journal (Refereed)
    Abstract [en]

    Extramatrical mycelia (EMM) of ectomycorrhizal fungi are important in carbon (C) and nitrogen (N) cycling in forests, but poor knowledge about EMM biomass and necromass turnovers makes the quantification of their role problematic. We studied the impacts of elevated CO2 and N fertilization on EMM production and turnover in a Pinus taeda forest. EMM C was determined by the analysis of ergosterol (biomass), chitin (total bio- and necromass) and total organic C (TOC) of sand-filled mycelium in-growth bags. The production and turnover of EMM bio- and necromass and total C were estimated by modelling. N fertilization reduced the standing EMM biomass C to 57% and its production to 51% of the control (from 238 to 122 kg C ha(-1)  yr(-1) ), whereas elevated CO2 had no detectable effects. Biomass turnover was high (˜13 yr(-1) ) and unchanged by the treatments. Necromass turnover was slow and was reduced from 1.5 yr(-1) in the control to 0.65 yr(-1) in the N-fertilized treatment. However, TOC data did not support an N effect on necromass turnover. An estimated EMM production ranging from 2.5 to 6% of net primary production stresses the importance of its inclusion in C models. A slow EMM necromass turnover indicates an importance in building up forest humus.

  • 22.
    Ekblad, Alf
    et al.
    Örebro University, School of Science and Technology. Swedish University of Agricultural Sciences, Umeå, Sweden.
    Nordgren, Anders
    Swedish University of Agricultural Sciences, Umeå, Sweden.
    Is growth of soil microorganisms in boreal forests limited by carbon or nitrogen availability?2002In: Plant and Soil, ISSN 0032-079X, E-ISSN 1573-5036, Vol. 242, no 1, p. 115-122Article in journal (Refereed)
    Abstract [en]

    To study whether the biomass of soil microorganisms in a boreal Pinus sylvestris-Vaccinium vitis-idaea forest was limited by the availability of carbon or nitrogen, we applied sucrose from sugar cane, a C4 plant, to the organic mor-layer of the C3–C dominated soil. We can distinguish between microbial mineralization of the added sucrose and respiration of endogenous carbon (root and microbial) by using the C4-sucrose as a tracer, exploiting the difference in natural abundance of 13C between the added C4-sucrose (δ13C −10.8‰) and the endogenous C3–carbon (δ13C −26.6 ‰). In addition to sucrose, NH4Cl (340 kg N ha−1) was added factorially to the mor-layer. We followed the microbial activity for nine days after the treatments, by in situ sampling of CO2 evolved from the soil and mass spectrometric analyses of δ13C in the CO2. We found that microbial biomass was limited by the availability of carbon, rather than nitrogen availability, since there was a 50% increase in soil respiration in situ between 1 h and 5 days after adding the sucrose. However, no further increase was observed unless nitrogen was also added. Analyses of the δ13C ratios of the evolved CO2 showed that increases in respiration observed between 1 h and 9 days after the additions could be accounted for by an increase in mineralization of the added C4–C.

  • 23.
    Ekblad, Alf
    et al.
    Swedish University of Agricultural Sciences, Umeå, Sweden.
    Nyberg, Gert
    Swedish University of Agricultural Sciences, Umeå, Sweden.
    Högberg, Peter
    Swedish University of Agricultural Sciences, Umeå, Sweden.
    C-13-discrimination during microbial respiration of added C-3-, C-4- and C-13-labelled sugars to a C-3-forest soil2002In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 131, no 2, p. 245-249Article in journal (Refereed)
    Abstract [en]

    We tested whether 13C-discrimination during microbial respiration, or during CO2 sampling in the field, can explain changes observed in the δ13C of emitted CO2 that follow the addition of C4-sucrose, as a microbial substrate, to the soil of a C3-ecosystem. We approached this problem by adding C3-glucose (δ13C=–23.4‰), C4-sucrose (–10.8‰) or 13C-labelled glucose (103.7‰) to the intact mor layer, the upper organic soil (–26.5‰, bulk soil organic matter), of a boreal Pinus sylvestris L. forest. If 13C-discrimination is significant, it should generate illusory differences in the calculated contributions from the added C and endogenous C3-C to total soil respiration, when C4-sucrose or 13C-labelled glucose is added. Further, if discrimination occurs, we should also be able to detect a shift in the δ13C of respired CO2 after the addition of C3-glucose. The addition of the three sugar solutions gave similar increases in soil respiration (up to a doubling 1 h after the additions), while the addition of water gave no increase in respiration. There was no change in δ13C of the emitted CO2 after additions of H2O or C3-glucose. In contrast, the addition of C4-sucrose and 13C-labelled glucose gave δ13C values of evolved CO2 that were 4.5‰ and 30.3‰ higher than the pre-sugar values, respectively. The calculated respiration rates of the added carbon sources, C4-C or 13C-labelled C, were very similar. Also, we found very similar sugar-induced increases in respiration of endogenous C3-C in the plots supplied with C4-sucrose and 13C-labelled glucose, accounting for about 50% of the total increase in respiration 1 h after addition. Our results confirm that any microbial 13C-discrimination during respiration is minor.

  • 24.
    Ekblad, Alf
    et al.
    University of Umeå, Umeå, Sweden.
    Näsholm, Torgny
    Swedish University of Agricultural Sciences, Umeå, Sweden.
    Determination of chitin in fungi and mycorrhizal roots by an improved HPLC analysis of glucosamine1996In: Plant and Soil, ISSN 0032-079X, E-ISSN 1573-5036, Vol. 178, no 1, p. 29-35Article in journal (Refereed)
    Abstract [en]

    A method to measure chitin content in fungi and ectomycorrhizal roots with high-performance liquid chromatography (HPLC) was developed. Measurements of fluorescence of 9-fluorenylmethylchloroformate (FMOC-CI) derivatives of glucosamine were made on acid hydrolysates of pure chitin, chitin-root mixtures and fungal-root mixtures. The method was applied on 5 isolates of ectomycorrhizal fungi, and ectomycorrhizal and non-mycorrhizal Pinus sylvestris roots. Interference from amino acids was removed by pre-treatment of samples with 0.2 N NaOH. This pre-treatment did not reduce the recovery of chitin, nor did plant material affect the recovery of chitin. The HPLC method was compared with a colorimetric chitin-method by measurements on root-fungal mixtures, with known fungal content. The HPLC method gave estimates of fungal biomass which were equal to the expected while the colorimetric method showed values significantly (p<0.001) lower than the expected. The present chitin method offers a sensitive and specific tool for the quantification of chitin in fungi and in ectomycorrhizal roots.

  • 25.
    Ekblad, Alf
    et al.
    Örebro University, School of Science and Technology.
    Wallander, H.
    Godbold, D. L.
    Cruz, C.
    Johnson, D.
    Baldrian, P.
    Björk, Robert
    Örebro University, School of Science and Technology.
    Epron, D.
    Kieliszewska-Rokicka, B.
    Kjoller, R.
    Kraigher, H.
    Matzner, E.
    Neumann, J.
    Plassard, C.
    The production and turnover of extramatrical mycelium of ectomycorrhizal fungi in forest soils: role in carbon cycling2013In: Plant and Soil, ISSN 0032-079X, E-ISSN 1573-5036, Vol. 366, no 1-2, p. 1-27Article, review/survey (Refereed)
    Abstract [en]

    There is growing evidence of the importance of extramatrical mycelium (EMM) of mycorrhizal fungi in carbon (C) cycling in ecosystems. However, our understanding has until recently been mainly based on laboratory experiments, and knowledge of such basic parameters as variations in mycelial production, standing biomass and turnover as well as the regulatory mechanisms behind such variations in forest soils is limited. Presently, the production of EMM by ectomycorrhizal (EM) fungi has been estimated at similar to 140 different forest sites to be up to several hundreds of kg per ha per year, but the published data are biased towards Picea abies in Scandinavia. Little is known about the standing biomass and turnover of EMM in other systems, and its influence on the C stored or lost from soils. Here, focussing on ectomycorrhizas, we discuss the factors that regulate the production and turnover of EMM and its role in soil C dynamics, identifying important gaps in this knowledge. C availability seems to be the key factor determining EMM production and possibly its standing biomass in forests but direct effects of mineral nutrient availability on the EMM can be important. There is great uncertainty about the rate of turnover of EMM. There is increasing evidence that residues of EM fungi play a major role in the formation of stable N and C in SOM, which highlights the need to include mycorrhizal effects in models of global soil C stores.

  • 26.
    Ekblad, Alf
    et al.
    Umeå University, Umeå, Sweden.
    Wallander, Håkan
    Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Carlsson, Rolf
    Umeå University, Umeå, Sweden.
    Huss-Danell, Kerstin
    Umeå University, Umeå, Sweden.
    Fungal biomass in roots and extramatrical mycelium in relation to macronutrients and plant biomass of ectomycorrhizal Pinus sylvestris and Alnus incana1995In: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 131, no 4, p. 443-451Article in journal (Refereed)
    Abstract [en]

    Summary

    We studied the effects of macronutrients on the production and distribution of fungal biomass and plant biomass in ectomycorrhizal (Paxillus involutus (Fr.) Fr.) or non-mycorrhiza] Pinus sylvestris L, and Alnus incana (L.) Moench. Fungal biomass was measured as ergosterol content in roots and extramatrical mycelium, Alnus infants was nodulated with Frankia. All six macronutrients were varied according to a two-level fractional factorial design, The plants were grown in pots during two growing periods in a growth chamber. Levels of N, P and sometimes K and interactions between them, had highly significant effects, whereas Ca. Mg and S had no significant effects. The production of extramatrical mycelial biomass peaked when P was low and other nutrients were high. This investment in extramatrical mycelium resulted in a 660%, higher biomass in mycorrhizal compared with non-mycorrhizal P. sylvestris at this nutrient regime. The proportion of fungal biomass in roots was stable in P. sylvestris hut more variable in A. incana. Alnus incana grew less when mycorrhizal then when non-mycorrhizal. The growth responses to mycorrhiza and to the different nutrient treatments were evident at the end of the first growing period. Non-mycorrhizal P. sylvestris did not respond to P limitation by a production of proportionally more roots. This might be a reflection of an obligate dependency on mycorrhiza for effective P uptake. By contrast, the root/shoot ratio in both mycorrhizal and non-mycorrhiza] P. sylvestris decreased strongly in response to increased N. The opposite root/shoot response was found in Alnus incana, and the ratio decreased strongly in response to increased P and increased in response to increased N.

  • 27.
    Ekblad, Alf
    et al.
    Swedish University of Agricultural Sciences, Umeå, Sweden.
    Wallander, Håkan
    Lund University, Lund, Sweden.
    Näsholm, Torgny
    Swedish University of Agricultural Sciences, Umeå, Sweden.
    Chitin and ergosterol combined to measure total and living fungal biomass in ectomycorrhizas1998In: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 138, no 1, p. 143-149Article in journal (Refereed)
    Abstract [en]

    We have studied the chitin and ergosterol contents of ectomycorrhizal roots in three sets of experiments to evaluate them as indicators of fungal biomass. The first set of experiments showed that ageing had a marked effect on ergosterol concentrations. The ergosterol content of 7-month-old, brown, shrunken Pinus sylvestris L.–Paxillus involutus (Fr.) Fr. mycorrhizas was found to be only 10% of that found in white, turgid, 1- or 4-month-old specimens. This supports the hypothesis that the compound is a good indicator of living fungal biomass. Ageing had a lesser effect on chitin concentrations since the chitin levels found in 7-month-old mycorrhizas were still 60% of the levels found in 1- and 4-month-old specimens.

    Consequently, the chitin∶ergosterol ratio increased from about 14 to 19 in 1- and 4-month-old mycorrhizas respectively to about 110 in 7-month-old mycorrhizas. In the second set of experiments, we found that variation in plant growth had no effect on the chitin∶ergosterol ratio in whole root systems of either Alnus incana (L.) Moench or Pinus sylvestris mycorrhizal with Paxillus involutus. In the third set of experiments, we found a constant relationship between the two marker concentrations in 10-month-old root systems of Pinus sylvestris, regardless of fungal species involved, using Paxillus involutus, Piloderma croceum Erikss. & Hjorts and Suillus variegatus (Fr.) O. Kuntze as test organisms. Taken together, the results of this study suggest that both chitin and ergosterol give reliable, but different, relative measures of fungal biomass in mycorrhizal roots. Furthermore, we demonstrate that, in combination, the two chemical markers can be used to estimate both total and living fungal biomass (derived from the chitin∶ergosterol ratio).

  • 28.
    Eriksson, Ulrika
    et al.
    Örebro University, School of Science and Technology.
    Roos, Anna
    Swedish Museum of Natural History, Stockholm, Sweden.
    Lind, Ylva
    Swedish Museum of Natural History, Stockholm, Sweden.
    Hope, Kjell
    Örebro University, School of Science and Technology.
    Ekblad, Alf
    Örebro University, School of Science and Technology.
    Kärrman, Anna
    Örebro University, School of Science and Technology.
    Comparison of PFASs contamination in the freshwater and terrestrial environments by analysis of eggs from osprey (Pandion haliaetus), tawny owl (Strix aluco), and common kestrel (Falco tinnunculus)2016In: Environmental Research, ISSN 0013-9351, E-ISSN 1096-0953, Vol. 149, p. 40-47Article in journal (Refereed)
    Abstract [en]

    The level of PFAS (per- and polyfluorinated alkyl substances) contamination in freshwater and terrestrial Swedish environments in 2013/2014 was assessed by analyzing a range of perfluorinated alkyl acids, fluorotelomer acids, sulfonamides, sulfonamidoethanols and polyfluoralkyl phosphate diesters (diPAPs) in predator bird eggs. Stable isotopes ((13)C and (15)N) were analyzed to elucidate the dietary source. The tawny owl (Strix aluco, n=10) and common kestrel (Falco tinnunculus, n=40), two terrestrial species, and the osprey (Pandion haliaetus, n=30), a freshwater specie were included. In addition, a temporal trend (1997-2001, 2008-2009, 2013) in osprey was studied as well. The PFAS profile was dominated by perfluorooctane sulfonic acid (PFOS) in eggs from osprey and tawny owl, while for common kestrel perfluorinated carboxylic acids (∑PFCA) exceeded the level of PFOS. PFOS concentration in osprey eggs remained at the same level between 1997 and 2001 and 2013. For the long-chained PFCAs, there were a significant increase in concentrations in osprey eggs between 1997 and 2001 and 2008-2009. The levels of PFOS and PFCAs were about 10 and five times higher, respectively, in osprey compared to tawny owl and common kestrel. Evidence of direct exposure from PFCA precursor compounds to birds in both freshwater and terrestrial environment was observed. Low levels of diPAPs were detected in a few samples of osprey (<0.02-2.4ng/g) and common kestrel (<0.02-0.16ng/g) eggs, and 6:2 FTSA was detected in a majority of the osprey eggs (<6.3-52ng/g). One saturated telomer acid (7:3 FTCA), which is a transformation marker from precursor exposure, was detected in all species (<0.24-2.7ng/g). The (15)N data showed higher levels in osprey eggs compared to tawny owl and common kestrel, indicating that they feed on a 2-3 times higher trophic level. We conclude that ospreys are continuously exposed to PFAS at levels where adverse toxic effects have been observed in birds.

  • 29.
    Franklin, Oskar
    et al.
    Swedish University of Agricultural Sciences, Uppsala, Sweden .
    Högberg, Peter
    Swedish University of Agricultural Sciences, Umeå, Sweden .
    Ekblad, Alf
    Örebro University, School of Science and Technology.
    Ågren, Göran I
    Swedish University of Agricultural Sciences, Uppsala, Sweden .
    Pine forest floor carbon accumulation in response to N and PK additions: Bomb C-14 modelling and respiration studies2003In: Ecosystems (New York. Print), ISSN 1432-9840, E-ISSN 1435-0629, Vol. 6, no 7, p. 644-658Article in journal (Refereed)
    Abstract [en]

    The addition of nitrogen via deposition alters the carbon balance of temperate forest ecosystems by affecting both production and decomposition rates. The effects of 20 years of nitrogen (N) and phosphorus and potassium (PK) additions were studied in a 40-year-old pine stand in northern Sweden. Carbon fluxes of the forest floor were reconstructed using a combination of data on soil 14C, tree growth, and litter decomposition. N-only additions caused an increase in needle litterfall, whereas both N and PK additions reduced long-term decomposition rates. Soil respiration measurements showed a 40% reduction in soil respiration for treated compared to control plots. The average age of forest floor carbon was 17 years. Predictions of future soil carbon storage indicate an increase of around 100% in the next 100 years for the N plots and 200% for the NPK plots. As much as 70% of the increase in soil carbon was attributed to the decreased decomposition rate, whereas only 20% was attributable to increased litter production. A reduction in decomposition was observed at a rate of N addition of 30 kg C ha−1 y−1, which is not an uncommon rate of N deposition in central Europe. A model based on the continuous-quality decomposition theory was applied to interpret decomposer and substrate parameters. The most likely explanations for the decreased decomposition rate were a fertilizer-induced increase in decomposer efficiency (production-to-assimilation ratio), a more rapid rate of decrease in litter quality, and a decrease in decomposer basic growth rate.

  • 30.
    Geng, Dawei
    et al.
    Örebro University, School of Science and Technology.
    Ericson Jogsten, Ingrid
    Örebro University, School of Science and Technology.
    Kukucka, Petr
    Örebro University, School of Science and Technology. RECETOX Masaryk University, Brno, Czech Republic.
    Eriksson, Ulrika
    Örebro University, School of Science and Technology.
    Ekblad, Alf
    Örebro University, School of Science and Technology.
    Grahn, Hans
    Örebro University, School of Science and Technology.
    Roos, Anna
    Department for Environmental Research and Monitoring, Swedish Museum of Natural History, Stockholm, Sweden.
    Temporal Trends of Polychlorinated Biphenyls, Organochlorine Pesticides and Polybrominated Diphenyl Ethers in Osprey Eggs in Sweden over the Years 1966 – 2013Manuscript (preprint) (Other academic)
  • 31.
    Gkarmiri, Konstantia
    et al.
    Department of Forest Mycology and Plant Pathology, Uppsala BioCenter, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Mahmood, Shahid
    Department of Forest Mycology and Plant Pathology, Uppsala BioCenter, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Ekblad, Alf
    Örebro University, School of Science and Technology.
    Alström, Sadhna
    Department of Forest Mycology and Plant Pathology, Uppsala BioCenter, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Högberg, Nils
    Department of Forest Mycology and Plant Pathology, Uppsala BioCenter, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Finlay, Roger
    Department of Forest Mycology and Plant Pathology, Uppsala BioCenter, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Identifying the Active Microbiome Associated with Roots and Rhizosphere Soil of Oilseed Rape2017In: Applied and Environmental Microbiology, ISSN 0099-2240, E-ISSN 1098-5336, Vol. 83, no 22, article id e01938-17Article in journal (Refereed)
    Abstract [en]

    RNA stable isotope probing and high-throughput sequencing were used to characterize the active microbiomes of bacteria and fungi colonizing the roots and rhizosphere soil of oilseed rape to identify taxa assimilating plant-derived carbon following (13)CO2 labeling. Root- and rhizosphere soil-associated communities of both bacteria and fungi differed from each other, and there were highly significant differences between their DNA- and RNA-based community profiles. Verrucomicrobia, Proteobacteria, Planctomycetes, Acidobacteria, Gemmatimonadetes, Actinobacteria, and Chloroflexi were the most active bacterial phyla in the rhizosphere soil. Bacteroidetes were more active in roots. The most abundant bacterial genera were well represented in both the (13)C- and (12)C-RNA fractions, while the fungal taxa were more differentiated. Streptomyces, Rhizobium, and Flavobacterium were dominant in roots, whereas Rhodoplanes and Sphingomonas (Kaistobacter) were dominant in rhizosphere soil. "Candidatus Nitrososphaera" was enriched in (13)C in rhizosphere soil. Olpidium and Dendryphion were abundant in the (12)C-RNA fraction of roots; Clonostachys was abundant in both roots and rhizosphere soil and heavily (13)C enriched. Cryptococcus was dominant in rhizosphere soil and less abundant, but was (13)C enriched in roots. The patterns of colonization and C acquisition revealed in this study assist in identifying microbial taxa that may be superior competitors for plant-derived carbon in the rhizosphere of Brassica napusIMPORTANCE This microbiome study characterizes the active bacteria and fungi colonizing the roots and rhizosphere soil of Brassica napus using high-throughput sequencing and RNA-stable isotope probing. It identifies taxa assimilating plant-derived carbon following (13)CO2 labeling and compares these with other less active groups not incorporating a plant assimilate. Brassica napus is an economically and globally important oilseed crop, cultivated for edible oil, biofuel production, and phytoextraction of heavy metals; however, it is susceptible to several diseases. The identification of the fungal and bacterial species successfully competing for plant-derived carbon, enabling them to colonize the roots and rhizosphere soil of this plant, should enable the identification of microorganisms that can be evaluated in more detailed functional studies and ultimately be used to improve plant health and productivity in sustainable agriculture.

  • 32. Hagedorn, Frank
    et al.
    Hiltbrunner, David
    Streit, Kathrin
    Ekblad, Alf
    Örebro University, School of Science and Technology.
    Lindahl, Bjorn
    Miltner, Anja
    Frey, Beat
    Handa, I. Tanya
    Haettenschwiler, Stephan
    Nine years of CO2 enrichment at the alpine treeline stimulates soil respiration but does not alter soil microbial communities2013In: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 57, p. 390-400Article in journal (Refereed)
    Abstract [en]

    Elevated atmospheric CO2 was often shown to stimulate belowground C allocation, but it is uncertain if this increase also alters the structure of soil microbial communities. Here, we assessed the effects of nine years of CO2 enrichment on soil microbial communities of an alpine treeline ecosystem with 35-year-old Lath decidua and Pinus mugo ssp. uncinata trees. We also tracked the C-13 signal of supplemental CO2 in soil-respired CO2, microbial biomass, and phospholipid fatty acids (PLFA) in undisturbed mor-type organic layers. We found a persistently increased soil CO2 efflux (+24% on average), but negligible effects of elevated CO2 on the biomass and community structure of soil microorganisms under both tree species determined with PLFA and T-RFLP (terminal restriction fragment length polymorphism). The C-13 tracing over 9 years revealed that 24-40% of the soil microbial biomass was composed of 'new' plant-derived C. PLFA from gram-negative biomarkers did not significant shift in C-13 by the CO2 addition, while those of gram-negative bacteria were significantly altered. The highest C-13 signals in individual PLFA was found in the fatty acid 18:26)6,9 with 65-80% new C, indicating that new plant-derived C was primarily incorporated by soil fungi. However, CO2 enrichment did not affect the production of mycelia biomass and the structure and composition of the fungal communities analysed by high-throughput 454-sequencing of genetic markers. Collectively, our results suggest that C flux through the plant soil system will be accelerated but that the biomass and composition of microbial communities will be little affected by rising atmospheric CO2 in organic matter rich treeline soils.

  • 33.
    Hagenbo, Andreas
    et al.
    Department of Forest Mycology and Plant Pathology, Uppsala BioCenter, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Clemmensen, Karina E.
    Department of Forest Mycology and Plant Pathology, Uppsala BioCenter, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Finlay, Roger D.
    Department of Forest Mycology and Plant Pathology, Uppsala BioCenter, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Kyaschenko, Julia
    Department of Soil and Environment, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Lindahl, Björn D.
    Department of Soil and Environment, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Fransson, Petra
    Department of Forest Mycology and Plant Pathology, Uppsala BioCenter, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Ekblad, Alf
    Örebro University, School of Science and Technology.
    Changes in turnover rather than production regulate biomass of ectomycorrhizal fungal mycelium across a Pinus sylvestris chronosequence2017In: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 214, no 1, p. 424-431Article in journal (Refereed)
    Abstract [en]

    In boreal forest soils, ectomycorrhizal fungi are fundamentally important for carbon (C) dynamics and nutrient cycling. Although their extraradical mycelium (ERM) is pivotal for processes such as soil organic matter build-up and nitrogen cycling, very little is known about its dynamics and regulation.

    In this study, we quantified ERM production and turnover, and examined how these two processes together regulated standing ERM biomass in seven sites forming a chronosequence of 12- to 100-yr-old managed Pinus sylvestris forests. This was done by determining ERM biomass, using ergosterol as a proxy, in sequentially harvested in-growth mesh bags and by applying mathematical models.

    Although ERM production declined with increasing forest age from 1.2 to 0.5 kg ha(-1)  d(-1) , the standing biomass increased from 50 to 112 kg ha(-1) . This was explained by a drastic decline in mycelial turnover from seven times to one time per year with increasing forest age, corresponding to mean residence times from 25 d up to 1 yr.

    Our results demonstrate that ERM turnover is the main factor regulating biomass across differently aged forest stands. Explicit inclusion of ERM parameters in forest ecosystem C models may significantly improve their capacity to predict responses of mycorrhiza-mediated processes to management and environmental changes.

  • 34.
    Huss-Danell, Kerstin
    et al.
    Department of Plant Physiology, University of Umeå, S-901 87, Umeå, Sweden .
    Lundquist, Per-Olof
    Department of Plant Physiology, University of Umeå, S-901 87, Umeå, Sweden .
    Ekblad, Alf
    Department of Plant Physiology, University of Umeå, S-901 87, Umeå, Sweden .
    Growth and acetylene reduction activity by intact plants of Alnus incana under field conditions1989In: Plant and Soil, ISSN 0032-079X, E-ISSN 1573-5036, Vol. 118, no 1-2, p. 61-73Article in journal (Refereed)
  • 35. Hyvönen, Riitta
    et al.
    Ågren, Göran I.
    Linder, Sune
    Persson, Tryggve
    Cotrufo, M. Francesca
    Ekblad, Alf
    Örebro University, Department of Natural Sciences.
    Freeman, Michael
    Grelle, Achim
    Janssens, Ivan A.
    Jarvis, Paul G.
    Kellomäki, Seppo
    Lindroth, Anders
    Loustau, Denis
    Lundmark, Tomas
    Norby, Richard J.
    Oren, Ram
    Pilegaard, Kim
    Ryan, Michael G.
    Sigurdsson, Bjarni D.
    Strömgren, Monika
    van Oijen, Marcel
    Wallin, Göran
    The likely impact of elevated [CO2], nitrogen deposition, increased temperature and management on carbon sequestration in temperate and boreal forest ecosystems: a literature review2007In: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 173, no 3, p. 463-480Article in journal (Other academic)
    Abstract [en]

    Temperate and boreal forest ecosystems contain a large part of the carbon stored on land, in the form of both biomass and soil organic matter. Increasing atmospheric [CO2], increasing temperature, elevated nitrogen deposition and intensified management will change this C store. Well documented single-factor responses of net primary production are: higher photosynthetic rate (the main [CO2] response); increasing length of growing season (the main temperature response); and higher leaf-area index (the main N deposition and partly [CO2] response). Soil organic matter will increase with increasing litter input, although priming may decrease the soil C stock initially, but litter quality effects should be minimal (response to [CO2], N deposition, and temperature); will decrease because of increasing temperature; and will increase because of retardation of decomposition with N deposition, although the

    rate of decomposition of high-quality litter can be increased and that of low-quality litter decreased. Single-factor responses can be misleading because of interactions between factors, in particular those between N and other factors, and indirect effects such as increased N availability from temperature-induced decomposition. In the long term the strength of feedbacks, for example the increasing demand for N from increased growth, will dominate over short-term responses to single factors. However, management has considerable potential for controlling the C store.

  • 36.
    Högberg, Peter
    et al.
    Swedish University of Agricultural Sciences, Umeå, Sweden.
    Ekblad, Alf
    Swedish University of Agricultural Sciences, Umeå, Sweden.
    Substrate-induced respiration measured in situ in a C-3-plant ecosystem using additions of C-4-sucrose1996In: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 28, no 9, p. 1131-1138Article in journal (Refereed)
    Abstract [en]

    We added sucrose derived from sugar cane, a tropical C4-plant, to the soil of a temperate C3-forest plant system. The combined measurement of CO2 respiration rate and 13C natural abundance of CO2 enabled a distinction to be made between C3- and C4-respiration, which offered new possibilities to analyze basal respiration and substrate-induced respiration (SIR) in the field. In tests in the laboratory, through-flow systems were used, while in the field the stationary gas phase under soil covers was sampled. Results from the laboratory and in the field were similar with an average SIR response of 2.2 (range 1.7–2.7) times the basal respiration. The change in δ13C after addition of C4-surcrose was less than expected from the increase in respiration rate. Calculations showed that there was an increased efflux of C3-carbon after the C4-sucrose addition. We describe mathematical models, by which we calculated the various source effects contributing to the measured response. The method has numerous advantages, e.g. it uses naturally labelled inexpensive non-hazardous compounds and measurements are non-destructive to the studied system.

  • 37.
    Högberg, Peter
    et al.
    Department of Forest Ecology, SLU, Umeå, Sweden.
    Ekblad, Alf
    Örebro University, School of Science and Technology.
    Nordgren, Anders
    Department of Forest Ecology, SLU, Umeå, Sweden.
    Plamboeck, Agneta H.
    Swedish Defence Research Agency Division of NBC-Defence, Umeå, Sweden.
    Ohlsson, Anders
    Department of Forest Ecology, SLU, Umeå, Sweden.
    Bhupinderpal-Singh, Singh
    Department of Forest Ecology, SLU, Umeå, Sweden.
    Högberg, Mona
    Department of Forest Ecology, SLU, Umeå, Sweden.
    Factors determining the 13C abundance of soil-respired CO2 in Boreal forests2005In: Stable isotopes and biosphere-atmosphere interactions: processes and biological controls / [ed] Lawrence B. Flanagan, James R. Ehleringer, Diane E. Pataki, Elsevier, 2005, p. 47-68Chapter in book (Refereed)
    Abstract [en]

    Analysis of the isotopic composition of the CO2 respired from soils may reveal information about the important component of the ecosystem C balance. This is crucial, since a large terrestrial sink for atmospheric CO2 has been located in the northern hemisphere, and the vast boreal forests may be largely responsible. At the same time, boreal and arctic ecosystems have large amounts of C stored in the soil, and could potentially become a source of CO2 in a warmer climate promoting more rapid decomposition of soil organic matter. Furthermore, the northern hemisphere has complex dynamics in terms of annual fluctuations in both the concentration of CO2 in the atmosphere and its δl3C. It is of utmost importance to understand the causes of this variability, since it interferes with the partitioning between the ocean and the terrestrial contributions in global models. This chapter aims to provide an update on the reviews by Flanagan and Ehleringer and Ehleringer et al. on the causation of the δ13C of the soil CO2 efflux and, in doing this, focuses on the boreal forests.

  • 38.
    Högberg, Peter
    et al.
    Swedish University of Agricultural Sciences, Umeå, Sweden.
    Högberg, Mona N
    Swedish University of Agricultural Sciences, Umeå, Sweden.
    Quist, Maud E
    Swedish University of Agricultural Sciences, Umeå, Sweden.
    Ekblad, Alf
    Swedish University of Agricultural Sciences, Umeå, Sweden.
    Näsholm, Torgny
    Swedish University of Agricultural Sciences, Umeå, Sweden.
    Nitrogen isotope fractionation during nitrogen uptake by ectomycorrhizal and non-mycorrhizal Pinus sylvestris1999In: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 142, no 3, p. 569-576Article in journal (Refereed)
    Abstract [en]

    An experiment was performed to find out whether ectomycorrhizal (ECM) fungi alter the nitrogen (N) isotope composition, δ15N, of N during the transport of N from the soil through the fungus into the plant. Non- mycorrhizal seedlings of Pinus sylvestris were compared with seedlings inoculated with either of three ECM fungi, Paxillus involutus, Suillus bovinus and S. variegatus. Plants were raised in sand in pots supplied with a nutrient solution with N given as either NH4+ or NO3. Fractionation against 15N was observed with both N sources; it decreased with increasing plant N uptake, and was larger when NH4+ was the source. At high ratios of Nuptake/Nsupplied there was no (NO3), or little (NH4+), fractionation. There seemed to be no difference in fractionation between ECM and non-mycorrhizal plants, but fungal rhizomorphs were sometimes enriched in 15N (up to 5‰ at most) relative to plant material; they were also enriched relative to the N source. However, this enrichment of the fungal material was calculated to cause only a marginal decrease (−0.1‰ in P. involutus) in δ15N of the N passing from the substrate through the fungus to the host, which is explained by the small size of the fungal N pool relative to the total N of the plant, i.e. the high efficiency of transfer. We conclude that the relatively high 15N abundance observed in ECM fungal species should be a function of fungal physiology in the ECM symbiosis, rather than a reflection of the isotopic signature of the N source(s) used. This experiment also shows that the δ15N of plant N is a good approximation of δ15N of the available N source(s), provided that N is limiting growth.

  • 39. Högberg, Peter
    et al.
    Nordgren, Anders
    Buchmann, Nina
    Taylor, Andrew F. S.
    Ekblad, Alf
    Örebro University, Department of Natural Sciences.
    Högberg, Mona N.
    Nyberg, Gert
    Ottosson-Löfvenius, Mikaell
    Read, David J.
    Large-scale forest girdling shows that current photosynthesis drives soil respiration2001In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 411, no 6839, p. 789-792Article in journal (Refereed)
    Abstract [en]

    The respiratory activities of plant roots, of their mycorrhizal fungi and of the free-living microbial heterotrophs (decomposers) in soils are significant components of the global carbon balance, but their relative contributions remain uncertain. To separate mycorrhizal root respiration from heterotrophic respiration in a boreal pine forest, we conducted a large-scale tree-girdling experiment, comprising 9 plots each containing about 120 trees. Tree-girdling involves stripping the stem bark to the depth of the current xylem at breast height terminating the supply of current photosynthates to roots and their mycorrhizal fungi without physically disturbing the delicate root-microbe-soil system. Here we report that girdling reduced soil respiration within 1-2 months by about 54% relative to respiration on ungirdled control plots, and that decreases of up to 37% were detected within 5 days. These values clearly show that the flux of current assimilates to roots is a key driver of soil respiration; they are conservative estimates of root respiration, however, because girdling increased the use of starch reserves in the roots. Our results indicate that models of soil respiration should incorporate measures of photosynthesis and of seasonal patterns of photosynthate allocation to roots.

  • 40.
    Johansson, Emma M.
    et al.
    Örebro University, School of Science and Technology.
    Fransson, Petra M. A.
    Department of Forest Mycology and Pathology, Swedish University of Agricultural Sciences.
    Ekblad, Alf
    Örebro University, School of Science and Technology.
    van Hees, Patrick A. W.
    Örebro University, School of Science and Technology.
    Autotrophic and heterotrophic soil respiration: the effects of non-mycorrhizal and mycorrhizal seedlings under elevated CO2Manuscript (preprint) (Other academic)
  • 41.
    Johansson, Veronika A.
    et al.
    Department of Ecology, Environment and Plant Sciences, Stockholm University, Stockholm, Sweden.
    Mikusinska, Ania
    Örebro University, School of Science and Technology.
    Ekblad, Alf
    Örebro University, School of Science and Technology.
    Eriksson, Ove
    Department of Ecology, Environment and Plant Sciences, Stockholm University, Stockholm, Sweden.
    Partial mycoheterotrophy in Pyroleae: nitrogen and carbon stable isotope signatures during development from seedling to adult2015In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 177, no 1, p. 203-211Article in journal (Refereed)
    Abstract [en]

    Mycoheterotrophic plants (MHP) are divided into non-photosynthesizing full MHP and green-leaved partial or initial MHP. We investigated 13C and 15N isotope enrichment in five putatively partial MHP species in the tribe Pyroleae (Ericaceae): Chimaphila umbellata, Moneses uniflora, Orthilia secunda, Pyrola chlorantha and Pyrola minor, sampled from forest sites on Öland, Sweden. For M. uniflora and P. chlorantha, we investigated isotope signatures of subterranean seedlings (which are mycoheterotrophic), to examine how the use of seedlings instead of full MHP species (Hypopitys monotropa) as reference species affects the assessment of partial mycoheterotrophy. Our main findings were as follows: (1) All investigated Pyroleae species were enriched in 15N compared to autotrophic reference plants. (2) significant fungal-derived C among the Pyroleae species was found for O. secunda and P. chlorantha. For the remaining species of C. umbellata, M. uniflora and P. minor, isotope signatures suggested adult autotrophy. (3) C and N gains, calculated using seedlings as a full MHP reference, yielded qualitatively similar results as when using H. monotropa as a reference. However, the estimated differences in C and N gains became larger when using seedlings as an MHP reference. (4) A previously unknown interspecific variation in isotope signature occurs during early ontogeny, from seed production to developing seedlings. Our findings suggest that there is a variation among Pyroleae species concerning partial mycoheterotrophy in adults. Adult autotrophy may be most common in Pyroleae species, and these species may not be as dependent on fungal-derived nutrients as some green orchids.

  • 42.
    Kyaschenko, Julia
    et al.
    Department of Soil and Environment, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Ovaskainen, Otso
    Organismal and Evolutionary Biology Research Programme, University of Helsinki, Finland; Centre for Biodiversity Dynamics, Department of Biology, Norwegian University of Science and Technology, Trondheim, Norway.
    Ekblad, Alf
    Örebro University, School of Science and Technology.
    Hagenbo, Andreas
    Department of Forest Mycology and Plant Pathology, Uppsala BioCenter, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Karltun, Erik
    Department of Soil and Environment, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Clemmensen, Karina E.
    Department of Forest Mycology and Plant Pathology, Uppsala BioCenter, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Lindahl, Björn D.
    Department of Soil and Environment, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Soil fertility in boreal forest relates to root-driven nitrogen retention and carbon sequestration in the mor layer2018In: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137Article in journal (Refereed)
    Abstract [en]

    Boreal forest soils retain significant amounts of carbon (C) and nitrogen (N) in purely organic layers, but the regulation of organic matter turnover and the relative importance of leaf litter and root‐derived inputs are not well understood.

    We combined bomb 14C dating of organic matter with stable isotope profiling for Bayesian parameterization of an organic matter sequestration model. C and N dynamics were assessed across annual depth layers (cohorts), together representing 256 yr of organic matter accumulation. Results were related to ecosystem fertility (soil inorganic N, pH and litter C : N).

    Root‐derived C was estimated to decompose two to 10 times more slowly than leaf litter, but more rapidly in fertile plots. The amounts of C and N per cohort declined during the initial 20 yr of decomposition, but, in older material, the amount of N per cohort increased, indicating N retention driven by root‐derived C.

    The dynamics of root‐derived inputs were more important than leaf litter dynamics in regulating the variation in organic matter accumulation along a forest fertility gradient. N retention in the rooting zone combined with impeded mining for N in less fertile ecosystems provides evidence for a positive feedback between ecosystem fertility and organic matter turnover.

  • 43.
    Ladd, Brenton
    et al.
    Facultad de Ciencias Ambientales, Universidad Científica del Sur, Lima, Peru; Earth and Environmental Sciences, Evolution and Ecology Research Centre, School of Biological, University of New South Wales, Sydney, Australia.
    Peri, Pablo L.
    Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET), Estación Experimental Agropecuaria (EEA), National Agricultural Technology Institute (INTA), Rio Gallegos, Argentina.
    Pepper, David A.
    Earth and Environmental Sciences, School of Biological, University of New South Wales, Sydney, Australia.
    Silva, Lucas C. R.
    Department of Land, Air and Water Resources, University of California, Davis, USA.
    Sheil, Douglas
    School of Environmental Science and Management, Southern Cross University, Lismore, Australia; Center for International Forestry Research (CIFOR), Bogor, Indonesia; Department of Ecology and Natural Resource Management, Norwegian University of Life Sciences, Ås, Norway.
    Bonser, Stephen P.
    Earth and Environmental Sciences, Evolution and Ecology Research Centre, School of Biological, University of New South Wales, Sydney, Australia.
    Laffan, Shawn W.
    Earth and Environmental Sciences, School of Biological, University of New South Wales, Sydney, Australia.
    Amelung, Wulf
    Soil Science and Soil Ecology, Institute of Crop Science and Resource Conservation (INRES), University of Bonn, Bonn, Germany.
    Ekblad, Alf
    Örebro University, School of Science and Technology.
    Eliasson, Peter
    Department of Physical Geography and Ecosystem Science, Lund University, Lund, Sweden.
    Bahamonde, Hector
    Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET), Estación Experimental Agropecuaria (EEA), National Agricultural Technology Institute (INTA), Rio Gallegos, Argentina.
    Duarte-Guardia, Sandra
    acultad de Ciencias Ambientales, Universidad Cienifica del Sur, Lima, Peru.
    Bird, Michael
    Department of Ecology, Swedish University of Agricultural Sciences (SLU), Uppsala, Sweden; Centre for Tropical Environmental and Sustainability Science, School of Earth and Environmental Sciences, James Cook University, Cairns, Australia .
    Carbon isotopic signatures of soil organic matter correlate with leaf area index across woody biomes2014In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 102, no 6, p. 1606-1611Article in journal (Refereed)
    Abstract [en]

    Leaf area index (LAI), a measure of canopy density, is a key variable for modelling and understanding primary productivity, and also water use and energy exchange in forest ecosystems. However, LAI varies considerably with phenology and disturbance patterns, so alternative approaches to quantifying stand-level processes should be considered. The carbon isotope composition of soil organic matter (C-13(SOM)) provides a time-integrated, productivity-weighted measure of physiological and stand-level processes, reflecting biomass deposition from seasonal to decadal time scales.

    Our primary aim was to explore how well LAI correlates with C-13(SOM) across biomes.

    Using a global data set spanning large environmental gradients in tropical, temperate and boreal forest and woodland, we assess the strength of the correlation between LAI and C-13(SOM); we also assess climatic variables derived from the WorldClim database.

    We found that LAI was strongly correlated with C-13(SOM), but was also correlated with Mean Temperature of the Wettest Quarter, Mean Precipitation of Warmest Quarter and Annual Solar Radiation across and within biomes.

    Synthesis. Our results demonstrate that C-13(SOM) values can provide spatially explicit estimates of leaf area index (LAI) and could therefore serve as a surrogate for productivity and water use. While C-13(SOM) has traditionally been used to reconstruct the relative abundance of C-3 versus C-4 species, the results of this study demonstrate that within stable C-3- or C-4-dominated biomes, C-13(SOM) can provide additional insights. The fact that LAI is strongly correlated to C-13(SOM) may allow for a more nuanced interpretation of ecosystem properties of palaeoecosystems based on palaeosol C-13 values.

  • 44.
    Lindwall, Frida
    et al.
    University of Gothenburg, Gothenburg, Sweden.
    Vowels, Tage
    University of Gothenburg, Gothenburg, Sweden.
    Ekblad, Alf
    Örebro University, School of Science and Technology.
    Bjork, Robert G.
    University of Gothenburg, Gothenburg, Sweden.
    Reindeer grazing has contrasting effect on species traits in Vaccinium vitis-idaea L. and Bistorta vivipara (L.) Gray2013In: Acta Oecologica, ISSN 1146-609X, E-ISSN 1873-6238, Vol. 53, p. 33-37Article in journal (Refereed)
    Abstract [en]

    That reindeer grazing can have large effects on plant communities is well known, but how reindeer grazing affects plant traits and plant carbon (C) and nitrogen (N) allocation has not been studied to the same extent. This study was conducted in a sub-arctic dry heath in northern Sweden. 17-year-old reindeer exclosures were used to test whether reindeer grazing affects the C:N ratio (a plant quality index), and the delta C-13 and delta N-15 (indicators of changes in C and N dynamics) as well as the C and N content of above- and below ground parts of the evergreen dwarf shrub Vaccinium vitis-idaea L. and the perennial forb Bistorta vivipara (L) Gray. A lower C:N ratio was found in B. vivipara compared to V. vitis-idaea suggesting a higher grazing pressure on that species. We found that grazing reduced the total C content, by 26%, and increased the delta N-15, by 1 parts per thousand, in the leaves of B. vivipara, while no changes were observed in V. vitis-idaea. Fine roots of B. vivipara had higher delta C-13 (1 parts per thousand) and delta N-15 (2.5 parts per thousand) than the leaves, while such differences were not found in V. vitis-idaea. The results also highlight the importance of analysing both above- and belowground plant parts when interpreting natural variations in delta C-13 and delta N-15. (C) 2013 The Authors. Published by Elsevier Masson SAS. All rights reserved.

  • 45.
    Lundberg, Peter
    et al.
    Linköping University, Linköping, Sweden.
    Ekblad, Alf
    Örebro University, School of Science and Technology. Swedish University of Agricultural Sciences, Umeå, Sweden.
    Nilsson, Mats
    Swedish University of Agricultural Sciences, Umeå, Sweden.
    C-13 NMR spectroscopy studies of forest soil microbial activity: glucose uptake and fatty acid biosynthesis2001In: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 33, no 4-5, p. 621-632Article in journal (Refereed)
    Abstract [en]

    The intimate association of soil microorganisms with the soil matrix complicates analysis of their metabolism, since thorough separation of intact cells from the matrix is very difficult using standard protocols. Thus, in the study reported here, in situ glucose decomposition and metabolism in humus from a coniferous forest soil was monitored and evaluated using ‘solution state’ 13C NMR, which can be used in a non-invasive manner. [U-13C] glucose was added at a concentration of 1.73 mmol C g−1 dry organic matter, which is known to allow maximal substrate induced respiration (SIR), and the microbial metabolism of the added C was followed over a period of 28 days. The data showed that ∼50% of the added glucose was consumed within three days, coinciding with the appearance of label in CH3, –CH2– and –CH=CH– groups, and in glycerol-carbons, suggesting that olefinic triacylglycerols were being formed, probably located in oil droplets. During days two to three, around 40% of the consumed glucose C was allocated into solid state components, about 40% was respired and about 20% was found as triglycerols. The triacylglycerol signal reached a maximum after 13 days, but subsequently declined by 60%, as the triacylglycerols were apparently consumed, by day 28 of the incubation. Our results indicate there was an initial formation of structural microbial C (solid state carbon) followed by formation of storage lipid C, which subsequently decreased, probably because it was used to provide the organisms with energy when the external energy source (i.e. the glucose) was depleted. The formation of unsaturated triacylglycerols, typical storage metabolites of eucaryotes, suggests that fungi were the most active organisms in the glucose degradation.

  • 46.
    Menichetti, Lorenzo
    et al.
    Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Ekblad, Alf
    Örebro University, School of Science and Technology.
    Katterer, T.
    Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Organic amendments affect delta C-13 signature of soil respiration and soil organic C accumulation in a long-term field experiment in Sweden2013In: European Journal of Soil Science, ISSN 1351-0754, E-ISSN 1365-2389, Vol. 64, no 5, p. 621-628Article in journal (Refereed)
    Abstract [en]

    The contribution of young and old soil organic carbon (SOC) pools to soil CO2 fluxes and specific respiration rates of these fluxes was determined by using C-13 signatures in the Ultuna long-term continuous soil organic matter experiment (C-SOME). Initiated in 1956, the experiment had a range of treatments amended organically and with mineral nitrogen fertilizer under C-3 cultivation until 1999, and thereafter under C-4 (maize) cultivation. In 2011, soil respiration was measured in situ prior to planting, during growth and after harvest. The contributions from C-4- and C-3-C as well as their specific respiration rates were estimated from C-13 differences in SOC and CO2 fluxes. The contributions from C-4-C sources were further separated into autotrophic and heterotrophic respiration by comparing respiration rates before and after harvest. Between 165 and 385g C-4-Cm-2 accumulated during 10years of maize growth, contributing between 4.9 and 8.1% to the total SOC stock. Although recent C-4-C had an average specific respiration rate that was 8.4-22.6 times greater than C-3-C, total soil respiration was generally equally split between C-3-C and C-4-C. Both pools are therefore important sources of CO2 in the overall C budget, and a crucial factor in accounting for SOC stock change caused by management. Experimental treatments influenced specific respiration rates of C-4 plant material and accumulation of SOC stock, demonstrating how greater SOC accumulation can be favoured by high-quality C inputs.

  • 47.
    Menichetti, Lorenzo
    et al.
    Department of Soil and Environment, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Ekblad, Alf
    Örebro University, School of Science and Technology.
    Kätterer, Thomas
    Department of Ecology, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Contribution of roots and amendments to soil carbon accumulation within the soil profile in a long-term field experiment in Sweden2015In: Agriculture, Ecosystems & Environment, ISSN 0167-8809, E-ISSN 1873-2305, Vol. 200, p. 79-87Article in journal (Refereed)
    Abstract [en]

    The contribution of different C inputs to organic carbon accumulation within the soil profile in the Ultuna long-term continuous soil organic matter experiment, established in 1956, was determined. Until 1999, C3-crops were grown at the site, but since then maize (C4) has been the only crop. The effect of a total of 10 different inorganic nitrogen and organic amendment treatments (4 Mg C ha−1 yr−1) on SOC in topsoil and subsoil after 53 years was evaluated and the contribution from maize roots to SOC after 10 years of cultivation was estimated.

    Soil organic carbon (SOC) and δ13C signature were measured down to 50 cm depth. The C content in the topsoil (0–20 cm depth) was 1.5% at the start of the experiment. After 53 years of treatments, the average topsoil C content varied between 0.9 and 3.8% of soil dry weight, with the open fallow having the lowest and the peat amended the highest value. Nitrogen seemed to promote C accumulation in the topsoil treatment effects were smaller below 20 cm depth and only two of the amendments (peat and sewage sludge) significantly affected SOC content down to 35 cm depth. Despite this, penetrometer measurements showed significant treatment differences of compaction below 41 cm depth, and although we could not explain these differences this presented some evidence of an initial treatment-induced subsoil differentiation. Ten years of maize growth affected the δ13C of SOC down to 22.5 cm depth, where it varied between −25.16 and −26.33(‰), and an isotopic mass balance calculation suggested that maize C accounted for 4–8% of total SOC in the topsoil. Until less than 2500 years ago the site was a post-glacial sea floor and the 14C data suggest that marine sediment C still dominates the SOC in deeper soil layers. Overall, the results suggest that 53 years of treatments has caused dramatic changes on the stored C in the topsoil in several of the treatments, while the changes in the subsoil is much less dramatic and a small C accumulation in the upper subsoil was found in two of the treatments.

    The contribution from roots to SOC accumulation was generally equal to or greater than the contribution from amendments. The retention coefficient of root-derived C in the topsoil was on average 0.30 ± 0.09, which is higher than usually reported in the literature for plant residues but confirms previous findings for the same experiment using another approach. This strengthens the conclusion that root-derived SOC contributed more to SOC than above-ground crop residues.

  • 48.
    Menichetti, Lorenzo
    et al.
    Department of Soil and Environment, Swedish University of Agricultural Sciences, Uppsala, Sweden .
    Houot, Sabine
    INRA, UMR Environnement et Grandes Cultures Thiverval-Grignon, Plaisir, France.
    Van Oort, Folkert
    Unit of Physico-Chemistry and Ecotoxicology of Soils from Contaminated Agrosystems, INRA Centre de Recherche de Versailles-Grignon, Versailles, France.
    Kätterer, Thomas
    Department of Ecology, Sveriges lantbruksuniversitet, Uppsala, Sweden.
    Christensen, Bent T.
    Department of Agroecology, Aarhus Universitet, Århus, Denmark.
    Chenu, Claire C.
    AgroParisTech Thiverval Grignon, Plaisir, France.
    Barré, Pierre
    Laboratoire de Géologie, Ecole Normale Superieure, Paris, France.
    Vasilyeva, Nadezda A.
    AgroParisTech,, Thiverval Grignon, France.
    Ekblad, Alf
    Örebro University, School of Science and Technology.
    Increase in soil stable carbon isotope ratio relates to loss of organic carbon: results from five long-term bare fallow experiments2015In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 177, no 3, p. 811-821Article in journal (Refereed)
    Abstract [en]

    Changes in the 12C/13C ratio (expressed as δ13C) of soil organic C (SOC) has been observed over long time scales and with depth in soil profiles. The changes are ascribed to the different reaction kinetics of 12C and 13C isotopes and the different isotopic composition of various SOC pool components. However, experimental verification of the subtle isotopic shifts associated with SOC turnover under field conditions is scarce. We determined δ13C and SOC in soil sampled during 1929–2009 in the Ap-horizon of five European long-term bare fallow experiments kept without C inputs for 27–80 years and covering a latitudinal range of 11°. The bare fallow soils lost 33–65 % of their initial SOC content and showed a mean annual δ13C increase of 0.008–0.024 ‰. The 13C enrichment could be related empirically to SOC losses by a Rayleigh distillation equation. A more complex mechanistic relationship was also examined. The overall estimate of the fractionation coefficient (ε) was −1.2 ± 0.3 ‰. This coefficient represents an important input to studies of long-term SOC dynamics in agricultural soils that are based on variations in 13C natural abundance. The variance of ε may be ascribed to site characteristics not disclosed in our study, but the very similar kinetics measured across our five experimental sites suggest that overall site-specific factors (including climate) had a marginal influence and that it may be possible to isolate a general mechanism causing the enrichment, although pre-fallow land use may have some impact on isotope abundance and fractionation.

  • 49.
    Mikusinska, Anna
    et al.
    Örebro University, School of Science and Technology.
    Persson, Tryggve
    Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Taylor, Andy F. S.
    The James Hutton Institute, Aberdeen, UK.
    Ekblad, Alf
    Örebro University, School of Science and Technology.
    Response of ectomycorrhizal extramatrical mycelium production and isotopic composition to in-growth bag size and soil fauna2013In: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 66, p. 154-162Article in journal (Refereed)
    Abstract [en]

    In-growth bags are increasingly used to study extramatrical mycelium (EMM) of ectomycorrhizal fungi in forest soils. In this paper we tested whether bag size and presence of soil fauna in bags influence the production, isotopic composition, carbon (C) and nitrogen (N) content of the EMM. Cylindrical in-growth mesh bags (2- or 5-cm-diameter; with or without openings - (1 or 2 mm), allowing faunal colonization or not) were harvested 37, 48, 81 and 283 days after installation in July and the EMM biomass was determined from elemental analyses of the extractable amount of mycelia. The occurrence of openings allowed animals to invade the bags but this did not affect the amount of EMM. We suggest further studies in this matter since the number of animals was low and variable. In the first harvest, mycelial biomass C was three times greater in 2-cm than in 5-cm-bags. After 81 days, mycelial biomass C was 54% greater in the 2-cm (54 kg ha(-1)) than in the 5-cm bags (35 kg ha(-1)). While total mycelial C did not change over winter, N content increased suggesting a role for the EMM in the storage of N from autumn to spring. The delta C-13 and delta N-15 of the EMM changed between the first three harvests. We hypothesize these changes to be mainly driven by changes in plant C and N sinks. The relation between the isotopic composition of sporocarp exploration type, plant roots and EMM is discussed. (C) 2013 Elsevier Ltd. All rights reserved.

  • 50.
    Nilsson, Christer
    et al.
    Umeå University, Umeå, Sweden.
    Ekblad, Alf
    Umeå University, Umeå, Sweden.
    Dynesius, Mats
    Umeå University, Umeå, Sweden.
    Backe, Susanne
    Umeå University, Umeå, Sweden.
    Gardfjell, Maria
    Umeå University, Umeå, Sweden.
    Carlberg, Björn
    Umeå University, Umeå, Sweden.
    Hellqvist, Sven
    Umeå University, Umeå, Sweden.
    Jansson, Roland
    Umeå University, Umeå, Sweden.
    A Comparison of Species Richness and Traits of Riparian Plants between a Main River Channel and Its Tributaries1994In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 82, no 2, p. 281-295Article in journal (Refereed)
    Abstract [en]

    Summary

    1 We examined differences in species richness and frequencies of vascular plants in the riverbank vegetation between the main channel of the Vindel River system and seven of its tributaries which spanned the same biogeographic range.

    2 Species richness per site was higher in the main channel than in the tributaries, both as a whole and for many species groups. The proportions of woody plants (phanerophytes and chamaephytes), geophytes, and natural species were higher in the tributaries, while the proportions of hemicryptophytes, ruderals, and short-floating species (i.e. species unable to float > 1 day) were higher in the main channel. Both types of river had species that were more than twice as frequent there than in the other category.

    3 The main channel had a high species richness at intermediate altitudes whereas the tributaries had least species at intermediate altitudes. Except for the highest altitudes, the tributaries also had a generally lower mean species richness than the main channel.

    4 Stepwise multiple regression analyses using 15 predictor variables explained stat- istically up to 85% of the floristic variation in the river system. Mean annual discharge and number of substrates explained most of the variation in five equations each, while peat cover explained most of the variation in four equations, and altitude and silt cover in one equation each. Mean annual discharge, peat cover and silt cover differed between the main channel and the tributaries and could therefore be responsible for the observed difference.

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