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New Phytol. 2015 Dec;208(4):1042-55. doi: 10.1111/nph.13547. Epub 2015 Jul 6.

The role of stoichiometric flexibility in modelling forest ecosystem responses to nitrogen fertilization.

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Biogeochemical Integration Department, Max Planck Institute for Biogeochemistry, Hans-Knöll-Str. 10, D-07745, Jena, Germany.
International Max Planck Research School (IMPRS) for Global Biogeochemical Cycles, Hans-Knöll-Str. 10, D-07745, Jena, Germany.


The response of the forest carbon (C) balance to changes in nitrogen (N) deposition is uncertain, partly owing to diverging representations of N cycle processes in dynamic global vegetation models (DGVMs). Here, we examined how different assumptions about the degree of flexibility of the ecosystem's C : N ratios contribute to this uncertainty, and which of these assumptions best correspond to the available data. We applied these assumptions within the framework of a DGVM and compared the results to responses in net primary productivity (NPP), leaf N concentration, and ecosystem N partitioning, observed at 22 forest N fertilization experiments. Employing flexible ecosystem pool C : N ratios generally resulted in the most convincing model-data agreement with respect to production and foliar N responses. An intermediate degree of stoichiometric flexibility in vegetation, where wood C : N ratio changes were decoupled from leaf and root C : N ratio changes, led to consistent simulation of production and N cycle responses to N addition. Assuming fixed C : N ratios or scaling leaf N concentration changes to other tissues, commonly assumed by DGVMs, was not supported by reported data. Between the tested assumptions, the simulated changes in ecosystem C storage relative to changes in C assimilation varied by up to 20%.


carbon-nitrogen cycle coupling; ecosystem modelling; fertilization; forest carbon balance; nitrogen cycle; plant stoichiometry

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