Contrasting effects of low and high nitrogen additions on soil CO2 flux components and ectomycorrhizal fungal sporocarp production in a boreal forest
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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DOI：
10.1111/gcb.12001
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发表时间：
2012-12-01
影响因子：
11.6
通讯作者：
Hogberg, Peter
中科院分区：
文献类型：
--
作者：
Hasselquist, Niles J.;Metcalfe, Daniel B.;Hogberg, Peter
通过大气沉降或作为肥料添加到北方和温带森林的氮（N）降低了土壤分解活性（异养呼吸）以及根系和菌根真菌的活性（自养呼吸）。然而，这些负面影响已被发现在研究中，应用相对较高的水平的N，而对环境大气N沉积速率的响应仍然不清楚。在这里，我们比较了一个未施肥的控制北方森林与施肥的森林（100公斤N公顷（-1）年（-1））和森林受到的N-沉积速率相当于在中欧（20公斤N公顷（-1）年（-1）），调查N添加率对森林地面呼吸和外生菌根真菌孢子果的生产的不同组成部分的影响。采用土环法对异养呼吸和自养呼吸进行了划分，并将其进一步划分为树根呼吸和菌根菌丝呼吸。低N地块的森林地面总呼吸是对照的两倍，而对照和高N地块之间没有差异。各样地的呼吸速率无显著差异。因此，在低N小区的森林地面呼吸增强的结果，增加R-a呼吸，增加R-tr呼吸，和R-m呼吸的两倍。后者证实了一个稍大的外生菌根（EM）真菌孢子果生产在低N地块相比，控制地块。与此相反，EM真菌子实体的生产几乎被消除，和R-m呼吸严重减少，在高N地块，这导致显着降低R-a呼吸。结果表明，土壤中的R-a组分对氮素添加速率的响应呈非线性，这需要进一步研究氮素添加速率与植物光合作用、碳分配之间的定量关系以及EM真菌的功能。
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.