Journal
GLOBAL CHANGE BIOLOGY
Volume 22, Issue 3, Pages 1299-1314Publisher
WILEY
DOI: 10.1111/gcb.13131
Keywords
carbon cost; Community Land Model; Fixation and Uptake of Nitrogen; mycorrhizal fungi; nitrogen uptake; net primary production
Funding
- US Department of Energy Office of Biological and Environmental Research Terrestrial Ecosystem Science Program
- US National Science Foundation Ecosystem Science Program
- Direct For Social, Behav & Economic Scie [1437591] Funding Source: National Science Foundation
- Division Of Behavioral and Cognitive Sci [1437591] Funding Source: National Science Foundation
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Plants typically expend a significant portion of their available carbon (C) on nutrient acquisition - C that could otherwise support growth. However, given that most global terrestrial biosphere models (TBMs) do not include the C cost of nutrient acquisition, these models fail to represent current and future constraints to the land C sink. Here, we integrated a plant productivity-optimized nutrient acquisition model - the Fixation and Uptake of Nitrogen Model - into one of the most widely used TBMs, the Community Land Model. Global plant nitrogen (N) uptake is dynamically simulated in the coupled model based on the C costs of N acquisition from mycorrhizal roots, nonmycorrhizal roots,N-fixing microbes, and retranslocation (from senescing leaves). We find that at the global scale, plants spend 2.4Pg C yr(-1) to acquire 1.0 Pg Nyr(-1), and that the C cost of N acquisition leads to a downregulation of global net primary production (NPP) by 13%. Mycorrhizal uptake represented the dominant pathway by which N is acquired, accounting for similar to 66% of the N uptake by plants. Notably, roots associating with arbuscular mycorrhizal (AM) fungi - generally considered for their role in phosphorus (P) acquisition - are estimated to be the primary source of global plant N uptake owing to the dominance of AM-associated plants in mid- and low-latitude biomes. Overall, our coupled model improves the representations of NPP downregulation globally and generates spatially explicit patterns of belowground C allocation, soil N uptake, and N retranslocation at the global scale. Such model improvements are critical for predicting how plant responses to altered N availability (owing to N deposition, rising atmospheric CO2, and warming temperatures) may impact the land C sink.
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