Publication Date:
2015-10-18
Description:
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 (FUN) model—into one of the most widely used TBMs, the Community Land Model (CLM). Global plant nitrogen (N) uptake is dynamically simulated in the coupled model based on the C costs of N acquisition from mycorrhizal roots, non-mycorrhizal roots, N-fixing microbes, and retranslocation (from senescing leaves). We find that at the global scale, plants spend 2.4 Pg C yr -1 to acquire 1.0 Pg N yr -1 , and that the C cost of N acquisition leads to a down-regulation of global net primary production (NPP) by 13%. Mycorrhizal uptake represented the dominant pathway by which N is acquired, accounting for ~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 representations of NPP down-regulation 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 CO 2 , warming temperatures) may impact the land C sink. This article is protected by copyright. All rights reserved.
Print ISSN:
1354-1013
Electronic ISSN:
1365-2486
Topics:
Biology
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Energy, Environment Protection, Nuclear Power Engineering
,
Geography
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