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Abstract:
Understanding the degree to which nitrogen (N) availability limits
land carbon (C) uptake under global environmental change
represents an unresolved challenge. First-generation ‘C-only’
vegetation models, lacking explicit representations of N cycling,
projected a substantial and increasing land C sink under rising
atmospheric CO2 concentrations. This prediction was questioned
for not taking into account the potentially limiting effect of N
availability, which is necessary for plant growth (Hungate et al.,
2003). More recent global models include coupled C and N cycles
in land ecosystems (C–N models) and are widely assumed to be
more realistic. However, inclusion of more processes has not
consistently improved their performance in capturing observed
responses of the global C cycle (e.g.Wenzel et al., 2014). With the
advent of a new generation of global models, including coupled
C, N, and phosphorus (P) cycling, model complexity is sure to
increase; but model reliability may not, unless greater attention is
paid to the correspondence of model process representations and
empirical evidence. It was in this context that the ‘Nitrogen Cycle
Workshop’ at Dartington Hall, Devon, UK was held on 1–5
February 2016. Organized by I. Colin Prentice and Benjamin D.
Stocker (Imperial College London, UK), the workshop was funded
by theEuropeanResearchCouncil,project ‘Earth systemModelBias
Reduction and assessing AbruptClimate change’ (EMBRACE).We
gathered empirical ecologists and ecosystem modellers to identify
key uncertainties in terrestrial C–N cycling, and to discuss processes that are missing or poorly represented in current models.
