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  • 1.
    Boström, Björn
    Örebro universitet, Institutionen för naturvetenskap.
    Achieving carbon isotope mass balance in northern forest soils, soil respiration and fungi2008Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Northern forests contain a large part of the global terrestrial carbon pool and it is unclear whether they will be sinks or sources for atmospheric carbon if the climate warms as predicted. Stable isotope techniques provide unique tools to study the carbon cycle at different scales but the interpretation of the isotope data is impaired by our inability to close the carbon isotope mass balance of ecosystems. This involves the paradox that the soil organic matter becomes increasingly 13C-enriched with increasing soil depth relative to the carbon input, plant litter, at the same time as soil respiration, the major carbon outflow from the soil, and fungi, organisms dependent on plant derived carbon, both are relatively 13C-enriched. I have determined the δ13C of the respired CO2 and the organic matter from different ecosystem components in a Norway spruce forest aiming at finding an explanation to the observed carbon isotope pattern.

    In the first study the soil surface respiration rate and isotopic composition was found to be governed by aboveground weather conditions the preceding 1-6 days. This suggests there is a fast flux of recent photosynthates to root respiration. In the second study I compared the respired CO2 from decomposition with the δ13C of the root free soil organic matter sampled from the litter layer down to 50 cm depth. Discrimination against 13C during respiration could not explain the 13C enrichment of soil organic matter with depth because the δ13C of the respired CO2 became increasingly 13C-enriched relative to the organic matter with soil depth. However, ~1.5‰ of the 2‰ 13C-gradient could be explained by the 13C depletion of atmospheric CO2 that has proceeded since the beginning of the 18th century due to the burning of fossil fuels and deforestation. The remaining shift was hypothesized to be due to a belowground contribution of 13C-enriched ectomycorrhizal derived carbon. In the third study I compared the δ13C of respired CO2 and sporocarps of ectomycorrhizal and saprotrophic fungi sampled in the spruce forest. The δ13C of respired CO2 and sporocarps were positively correlated and the differences in δ13C between CO2 and sporocarps were small, <±1‰ in nine out of 16 species, although 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). Loss of 13C-depleted CO2 may have enriched the biomass of some fungal species in 13C. However, the consistent 13C enrichment of fungal sporocarps and respired CO2 relative to the plant materials implies that other processes must be found to explain the consistent 13C-enrichment of fungal biomass compared to plant materials. In the final study, compound specific stable isotope analyses provided further evidence for the hypothesis that the biomass of ectomycorrhizal fungi are 13C-enriched relative to host biomass because the carbon provided by the host is 13C-enriched Furthermore, ectomycorrhizal fungi showed lower average δ13C values of metabolites than saprotrophs which gives further support for the so-called saprotrophic-mycorrhizal divide. I conclude that a belowground allocation of 13C-enriched carbon to ectomycorrhizal fungi closes the carbon isotope mass balance in boreal and temperate forest soils and explains the 13C-enriched soil respiration.

    Delarbeid
    1. Forest soil respiration rate and d13C is regulated by recent above ground weather conditions
    Åpne denne publikasjonen i ny fane eller vindu >>Forest soil respiration rate and d13C is regulated by recent above ground weather conditions
    2005 (engelsk)Inngår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 143, nr 1, s. 136-142Artikkel i tidsskrift (Fagfellevurdert) Published
    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.

    Emneord
    Air temperature, 13C, PLS time series analysis, Root respiration, Soil temperature
    HSV kategori
    Forskningsprogram
    Miljökemi
    Identifikatorer
    urn:nbn:se:oru:diva-2966 (URN)10.1007/s00442-004-1776-z (DOI)
    Tilgjengelig fra: 2008-04-14 Laget: 2008-04-14 Sist oppdatert: 2017-12-14bibliografisk kontrollert
    2. Isotope fractionation and 13C enrichment in soil profiles during the decomposition of soil organic matter
    Åpne denne publikasjonen i ny fane eller vindu >>Isotope fractionation and 13C enrichment in soil profiles during the decomposition of soil organic matter
    2007 (engelsk)Inngår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 153, nr 1, s. 89-98Artikkel i tidsskrift (Fagfellevurdert) Published
    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.

    sted, utgiver, år, opplag, sider
    Berlin: Springer, 2007
    Emneord
    C:N ratio, d13C, Forest soil organic matter, Isotopic discrimination, Microbial respiration
    HSV kategori
    Forskningsprogram
    Miljökemi
    Identifikatorer
    urn:nbn:se:oru:diva-4241 (URN)10.1007/s00442-007-0700-8 (DOI)17401582 (PubMedID)
    Tilgjengelig fra: 2007-12-07 Laget: 2007-12-07 Sist oppdatert: 2017-12-14bibliografisk kontrollert
    3. Can isotopic fractionation during respiration explain the 13C-enriched sporocarps of ectomycorrhizal and saprotrophic fungi?
    Åpne denne publikasjonen i ny fane eller vindu >>Can isotopic fractionation during respiration explain the 13C-enriched sporocarps of ectomycorrhizal and saprotrophic fungi?
    2008 (engelsk)Inngår i: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 177, nr 4, s. 1012-1019Artikkel i tidsskrift (Fagfellevurdert) Published
    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.

    sted, utgiver, år, opplag, sider
    Cambridge: Cambridge University Press, 2008
    Emneord
    Carbon/*metabolism, Carbon Dioxide/metabolism, Carbon Isotopes, Fungi/*metabolism, Nitrogen/metabolism, Nitrogen Isotopes, Oxygen Consumption/*physiology, Picea/microbiology, Time Factors, Trees/microbiology
    HSV kategori
    Forskningsprogram
    biologi
    Identifikatorer
    urn:nbn:se:oru:diva-4647 (URN)10.1111/j.1469-8137.2007.02332.x (DOI)18086229 (PubMedID)
    Tilgjengelig fra: 2008-10-20 Laget: 2008-10-20 Sist oppdatert: 2017-12-14bibliografisk kontrollert
    4. Carbon isotope ratios in ectomycorrhizal and saprotrophic metabolites in relation to the δ13C of substrate, sporocarps and respired CO2
    Åpne denne publikasjonen i ny fane eller vindu >>Carbon isotope ratios in ectomycorrhizal and saprotrophic metabolites in relation to the δ13C of substrate, sporocarps and respired CO2
    Vise andre…
    (engelsk)Manuskript (preprint) (Annet vitenskapelig)
    HSV kategori
    Forskningsprogram
    Biologi
    Identifikatorer
    urn:nbn:se:oru:diva-15539 (URN)
    Tilgjengelig fra: 2011-05-11 Laget: 2011-05-11 Sist oppdatert: 2017-10-17bibliografisk kontrollert
  • 2.
    Boström, Björn
    et al.
    Örebro universitet, Institutionen för naturvetenskap.
    Comstedt, Daniel
    Örebro universitet, Institutionen för naturvetenskap.
    Ekblad, Alf
    Örebro universitet, Institutionen för naturvetenskap.
    Can isotopic fractionation during respiration explain the 13C-enriched sporocarps of ectomycorrhizal and saprotrophic fungi?2008Inngår i: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 177, nr 4, s. 1012-1019Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 3.
    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.

  • 4.
    Boström, Björn
    et al.
    Örebro universitet, Institutionen för naturvetenskap.
    Ekblad, Alf
    Örebro universitet, Institutionen för naturvetenskap.
    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 Manuskript (preprint) (Annet vitenskapelig)
  • 5.
    Comstedt, Daniel
    et al.
    Örebro universitet, Institutionen för naturvetenskap.
    Boström, Björn
    Örebro universitet, Institutionen för naturvetenskap.
    Ekblad, Alf
    Örebro universitet, Institutionen för naturvetenskap.
    Autotrophic and heterotrophic soil respiration in a Norway spruce forest: estimating the root decomposition and soil moisture effects in a trenching experimentManuskript (Annet vitenskapelig)
  • 6.
    Comstedt, Daniel
    et al.
    Örebro universitet, Akademin för naturvetenskap och teknik.
    Boström, Björn
    Örebro universitet, Akademin för naturvetenskap och teknik.
    Ekblad, Alf
    Örebro universitet, Akademin för naturvetenskap och teknik.
    Autotrophic and heterotrophic soil respiration in a Norway spruce forest: estimating the root decomposition and soil moisture effects in a trenching experiment2011Inngår i: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 104, nr 1-3, s. 121-132Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 7.
    Comstedt, Daniel
    et al.
    Örebro universitet, Institutionen för naturvetenskap.
    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 tool2006Inngår i: Ecosystems (New York. Print), ISSN 1432-9840, E-ISSN 1435-0629, Vol. 9, nr 8, s. 1266-1277Artikkel i tidsskrift (Fagfellevurdert)
  • 8.
    Comstedt, Daniel
    et al.
    Örebro universitet, Institutionen för naturvetenskap.
    Boström, Björn
    Thompson, Matthew V.
    Ekblad, Alf
    A link between above ground weather conditions and the δ13C of forest soil respiration is not always observedManuskript (Annet vitenskapelig)
  • 9.
    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.

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