Datensatz

Zusammenfassung

The response of the forest carbon 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 examine how different assumptions about the degree of flexibility of the ecosystem’s C:N stoichiometry contribute to this uncertainty, and which of these assumptions best correspond to available data. We applied these assumptions within the framework of a DGVM and compared the results to responses in net primary productivity, leaf N content, and ecosystem N partitioning, observed at 22 forest N fertilisation 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 level of stoichiometric flexibility in vegetation, where wood C:N changes were decoupled from plant C:N changes, led to consistent similation of production and N cycle responses to N addition. The scaling of leaf N concentration changes to other tissues, commonly assumed by DGVMs, was not supported by reported ecosystem N partitioning. Our analysis further suggested that the purely heuristic way to simulate foliar N changes can lead to ecologically implausible results, which potentially could be reduced by considering resource-use efficiency.