Contrasting effects of low and high nitrogen additions on soil CO2 flux components and ectomycorrhizal fungal sporocarp production in a boreal forest

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Contrasting effects of low and high nitrogen additions on soil CO2 flux components and ectomycorrhizal fungal sporocarp production in a boreal forest. / Hasselquist, Niles J.; Metcalfe, Dan; Hogberg, Peter.

I: Global Change Biology, Vol. 18, Nr. 12, 2012, s. 3596-3605.

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T1 - Contrasting effects of low and high nitrogen additions on soil CO2 flux components and ectomycorrhizal fungal sporocarp production in a boreal forest

AU - Hasselquist, Niles J.

AU - Metcalfe, Dan

AU - Hogberg, Peter

PY - 2012

Y1 - 2012

N2 - Nitrogen (N) added through atmospheric deposition or as fertilizer to boreal and temperate forests reduces both soil decomposer activity (heterotrophic respiration) and the activity of roots and mycorrhizal fungi (autotrophic respiration). However, these negative effects have been found in studies that applied relatively high levels of N, whereas the responses to ambient atmospheric N deposition rates are still not clear. Here, we compared an unfertilized control boreal forest with a fertilized forest (100 kg N ha(-1) yr(-1)) and a forest subject to N-deposition rates comparable to those in Central Europe (20 kg N ha(-1) yr(-1)) to investigate the effects of N addition rate on different components of forest floor respiration and the production of ectomycorrhizal fungal sporocarps. Soil collars were used to partition heterotrophic (R-h) and autotrophic (R-a) respiration, which was further separated into respiration by tree roots (R-tr) and mycorrhizal hyphae (R-m). Total forest floor respiration was twice as high in the low N plot compared to the control, whereas there were no differences between the control and high N plot. There were no differences in R-h respiration among plots. The enhanced forest floor respiration in the low N plot was, therefore, the result of increased R-a respiration, with an increase in R-tr respiration, and a doubling of R-m respiration. The latter was corroborated by a slightly greater ectomycorrhizal (EM) fungal sporocarp production in the low N plot as compared to the control plot. In contrast, EM fungal sporocarp production was nearly eliminated, and R-m respiration severely reduced, in the high N plot, which resulted in significantly lower R-a respiration. We thus found a nonlinear response of the R-a components to N addition rate, which calls for further studies of the quantitative relations among N addition rate, plant photosynthesis and carbon allocation, and the function of EM fungi.

AB - Nitrogen (N) added through atmospheric deposition or as fertilizer to boreal and temperate forests reduces both soil decomposer activity (heterotrophic respiration) and the activity of roots and mycorrhizal fungi (autotrophic respiration). However, these negative effects have been found in studies that applied relatively high levels of N, whereas the responses to ambient atmospheric N deposition rates are still not clear. Here, we compared an unfertilized control boreal forest with a fertilized forest (100 kg N ha(-1) yr(-1)) and a forest subject to N-deposition rates comparable to those in Central Europe (20 kg N ha(-1) yr(-1)) to investigate the effects of N addition rate on different components of forest floor respiration and the production of ectomycorrhizal fungal sporocarps. Soil collars were used to partition heterotrophic (R-h) and autotrophic (R-a) respiration, which was further separated into respiration by tree roots (R-tr) and mycorrhizal hyphae (R-m). Total forest floor respiration was twice as high in the low N plot compared to the control, whereas there were no differences between the control and high N plot. There were no differences in R-h respiration among plots. The enhanced forest floor respiration in the low N plot was, therefore, the result of increased R-a respiration, with an increase in R-tr respiration, and a doubling of R-m respiration. The latter was corroborated by a slightly greater ectomycorrhizal (EM) fungal sporocarp production in the low N plot as compared to the control plot. In contrast, EM fungal sporocarp production was nearly eliminated, and R-m respiration severely reduced, in the high N plot, which resulted in significantly lower R-a respiration. We thus found a nonlinear response of the R-a components to N addition rate, which calls for further studies of the quantitative relations among N addition rate, plant photosynthesis and carbon allocation, and the function of EM fungi.

KW - autotrophic respiration

KW - carbon flux

KW - forest soil

KW - mycorrhiza

KW - nitrogen

KW - deposition

KW - Scots pine

KW - soil respiration partitioning

U2 - 10.1111/gcb.12001

DO - 10.1111/gcb.12001

M3 - Article

VL - 18

SP - 3596

EP - 3605

JO - Global Change Biology

JF - Global Change Biology

SN - 1354-1013

IS - 12

ER -