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  • 1.
    Andrén, O.
    et al.
    Departments of Ecology and Environmental Research, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Schnürer, Johan
    Department of Microbiology, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Barley straw decomposition with varied levels of microbial grazing by Folsomia fimetaria (L.) (Collembola, Isotomidae)1985Inngår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 68, nr 1, s. 57-62Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Folsomia fimetaria (L.) were added (0, 5, 10, 20 animals) to 0.100 g barley straw which had been inoculated 10 days (244 h) earlier with a natural soil microflora. Respiration (CO2 evolution) was monitored continuously. Mass loss, fungal standing crop (total and FDA-active), bacterial and protozoan biomass were estimated 42 days (1,000 h) after microbial inoculation. The degree of surface cover by hyphae was surveyed at regular intervals. No significant differences (P>0.05) were found in respiration, mass loss or microbial biomass, but the density of surface hyphae were reduced by addition of Collembola. Fungal production was low, less than 5% of the estimated microbial production, and could not account for all collembolan growth during incubation. F. fimetaria appeared to consume mainly bacteria and protozoa, and had little impact on carbon mineralization.

  • 2.
    Boström, Björn
    et al.
    Örebro universitet, Institutionen för naturvetenskap.
    Comstedt, Daniel
    Örebro universitet, Institutionen för naturvetenskap.
    Ekblad, Alf
    Örebro universitet, Institutionen för naturvetenskap.
    Isotope fractionation and 13C enrichment in soil profiles during the decomposition of soil organic matter2007Inngår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 153, nr 1, s. 89-98Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 3.
    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 universitet, Institutionen för naturvetenskap och teknik.
    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 study2013Inngår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 171, nr 3, s. 623-637Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 4.
    Ekblad, Alf
    et al.
    Örebro universitet, Institutionen för naturvetenskap.
    Boström, Björn
    Örebro universitet, Institutionen för naturvetenskap.
    Holm, Anders
    Örebro universitet, Institutionen för naturvetenskap.
    Comstedt, Daniel
    Örebro universitet, Institutionen för naturvetenskap.
    Forest soil respiration rate and d13C is regulated by recent above ground weather conditions2005Inngår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 143, nr 1, s. 136-142Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 5.
    Ekblad, Alf
    et al.
    Örebro universitet, Institutionen för naturvetenskap och teknik. 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 respiration2001Inngår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 127, nr 3, s. 305-308Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 6.
    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 soil2002Inngår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 131, nr 2, s. 245-249Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 7.
    Johansson, Veronika A.
    et al.
    Department of Ecology, Environment and Plant Sciences, Stockholm University, Stockholm, Sweden.
    Mikusinska, Ania
    Örebro universitet, Institutionen för naturvetenskap och teknik.
    Ekblad, Alf
    Örebro universitet, Institutionen för naturvetenskap och teknik.
    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 adult2015Inngår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 177, nr 1, s. 203-211Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 8.
    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 universitet, Institutionen för naturvetenskap och teknik.
    Increase in soil stable carbon isotope ratio relates to loss of organic carbon: results from five long-term bare fallow experiments2015Inngår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 177, nr 3, s. 811-821Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 9. Persson, Jörgen
    et al.
    Högberg, Peter
    Ekblad, Alf
    Örebro universitet, Institutionen för naturvetenskap.
    Högberg, Mona N.
    Nordgren, Anders
    Näsholm, Torgny
    Nitrogen acquisition from inorganic and organic sources by boreal forest plants in the field2003Inngår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 137, nr 2, s. 252-257Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A wide range of recent studies have indicated that organic nitrogen may be of great importance to plant nitrogen (N) nutrition. Most of these studies have, however, been conducted in laboratory settings, excluding important factors for actual plant uptake, such as competition, mycorrhizal associations and soil interactions. In order to accurately evaluate the importance of different N compounds to plant N nutrition, field studies are crucial. In this study, we investigated short- as well as long-term plant nitrogen uptake by Deschampsia flexuosa, Picea abies and Vaccinium myrtillus from 15NO3-, 15NH4+ and (U-13C, 15N) arginine, glycine or peptides. Root N uptake was analysed after 6 h and 64 days following injections. Our results show that all three species, irrespective of their type of associated mycorrhiza (arbuscular, ecto- or ericoid, respectively) rapidly acquired similar amounts of N from the entire range of added N sources. After 64 days, P. abies and V. myrtillus had acquired similar amounts of N from all N sources, while for D. flexuosa, the uptake from all N sources except ammonium was significantly lower than that from nitrate. Furthermore, soil analyses indicate that glycine was rapidly decarboxylated after injections, while other organic compounds exhibited slower turnover. In all, these results suggest that a wide range of N compounds may be of importance for the N nutrition of these boreal forest plants, and that the type of mycorrhiza may be of great importance for N scavenging, but less important to the N uptake capacity of plants.

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