Journal
GLOBAL BIOGEOCHEMICAL CYCLES
Volume 24, Issue -, Pages -Publisher
AMER GEOPHYSICAL UNION
DOI: 10.1029/2009GB003621
Keywords
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Funding
- U.K. Natural Environment Research Council (NERC), Quantifying Ecosystem Roles in the Carbon Cycle (QUERCC)
- Quantifying and Understanding the Earth System (QUEST)
- NERC [quest010002] Funding Source: UKRI
- Natural Environment Research Council [quest010002, ceh010023, ceh010024] Funding Source: researchfish
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Nitrogen (N) generally limits plant growth and controls biosphere responses to climate change. We introduce a new mathematical model of plant N acquisition, called Fixation and Uptake of Nitrogen (FUN), based on active and passive soil N uptake, leaf N retranslocation, and biological N fixation. This model is unified under the theoretical framework of carbon (C) cost economics, or resource optimization. FUN specifies C allocated to N acquisition as well as remaining C for growth, or N-limitation to growth. We test the model with data from a wide range of sites (observed versus predicted N uptake r(2) is 0.89, and RMSE is 0.003 kg N m(-2).yr(-1)). Four model tests are performed: (1) fixers versus nonfixers under primary succession; (2) response to N fertilization; (3) response to CO2 fertilization; and (4) changes in vegetation C from potential soil N trajectories for five DGVMs (HYLAND, LPJ, ORCHIDEE, SDGVM, and TRIFFID) under four IPCC scenarios. Nonfixers surpass the productivity of fixers after similar to 150-180 years in this scenario. FUN replicates the N uptake response in the experimental N fertilization from a modeled N fertilization. However, FUN cannot replicate the N uptake response in the experimental CO2 fertilization from a modeled CO2 fertilization; nonetheless, the correct response is obtained when differences in root biomass are included. Finally, N-limitation decreases biomass by 50 Pg C on average globally for the DGVMs. We propose this model as being suitable for inclusion in the new generation of Earth system models that aim to describe the global N cycle.
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