Nitrogen cycling and feedbacks in a global dynamic land model

Stefan Gerber, Hedin L.O., Oppenheimer M., Pacala S.W., Shevliakova, E.. Global Biogeochemical Cycles – 24, doi:10.1029/2008GB00333.

Stefan Gerber and his colleagues at Princeton Cooperative Institute for Climate studies published a paper describing Nitrogen (N) cycling and its feedbacks on terrestrial Carbon (C) in a new GFDL land model LM3V-N. The new model simulates how nitrogen nutrient availability affects carbon exchange between land and atmosphere, and improves constraints on feedbacks among CO₂, climate, and land dynamics in the GFDL Earth System Models.

The new model captures features that are known to be essential from empirical studies of forest and grassland ecosystems. It captures observed changes in forest net primary productivity under elevated CO₂ as in free-air CO₂ enrichment experiments (FACE). Modeled physical disturbance (i.e. removal of plant biomass) induces carbon-nitrogen (C-N) feedbacks expressed as increased soil nitrogen loss followed by vegetation recovery and nitrogen limitation. This is in line with theories and observations of successional vegetation dynamics. Finally, in contrast to other leading models, the model predicts a weakening of C-N feedbacks when ecosystem steady-state is approached.

The magnitude of the carbon feedback on climate change is one of the largest uncertainties in making future climate projections. This addition to the land model allows us to address this large uncertainty. It offers a more realistic representation of real-world terrestrial ecosystem dynamics.

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