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Abstract:
The LPJ-GUESS dynamic vegetation model
uniquely combines an individual- and patch-based representation
of vegetation dynamics with ecosystem biogeochemical
cycling from regional to global scales. We present an
updated version that includes plant and soil N dynamics,
analysing the implications of accounting for C–N interactions
on predictions and performance of the model. Stand
structural dynamics and allometric scaling of tree growth
suggested by global databases of forest stand structure and
development were well reproduced by the model in comparison
to an earlier multi-model study. Accounting for N cycle
dynamics improved the goodness of fit for broadleaved
forests. N limitation associated with low N-mineralisation
rates reduces productivity of cold-climate and dry-climate
ecosystems relative to mesic temperate and tropical ecosystems.
In a model experiment emulating free-air CO2 enrichment
(FACE) treatment for forests globally, N limitation associated
with low N-mineralisation rates of colder soils reduces
CO2 enhancement of net primary production (NPP) for
boreal forests, while some temperate and tropical forests exhibit
increased NPP enhancement. Under a business-as-usual
future climate and emissions scenario, ecosystem C storage
globally was projected to increase by ca. 10 %; additional
N requirements to match this increasing ecosystem C were
within the high N supply limit estimated on stoichiometric
grounds in an earlier study. Our results highlight the importance
of accounting for C–N interactions in studies of global terrestrial N cycling, and as a basis for understanding mechanisms on local scales and in different regional contexts.
