title: Carbon cost of plant nitrogen acquisition: global carbon cycle impact from an improved plant nitrogen cycle in the Community Land Model.
abstract: 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 2.4 Pg C yr(-1) to acquire 1.0 Pg N yr(-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 ~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.
authors.affiliation: Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA, 91109, USA.|Joint Institute for Regional Earth System Science and Engineering, University of California at Los Angeles, Los Angeles, CA, 90095, USA.
authors.forename: Mingjie
authors.initials: M
authors.lastname: Shi
authors.affiliation: Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA, 91109, USA.|Joint Institute for Regional Earth System Science and Engineering, University of California at Los Angeles, Los Angeles, CA, 90095, USA.
authors.forename: Joshua B
authors.initials: JB
authors.lastname: Fisher
authors.affiliation: Department of Biology, West Virginia University, 53 Campus Drive, Morgantown, WV, 26506, USA.
authors.forename: Edward R
authors.initials: ER
authors.lastname: Brzostek
authors.affiliation: Department of Biology, Indiana University, 702 N. Walnut Grove Avenue, Bloomington, IN, 47405, USA.
authors.forename: Richard P
authors.initials: RP
authors.lastname: Phillips
mesh_terms: D002244:Carbon / Q000378:metabolism; D057965:Carbon Sequestration; D017753:Ecosystem; D008962:Models, Theoretical; D009584:Nitrogen / Q000378:metabolism; D058458:Nitrogen Cycle; D010944:Plants / Q000378:metabolism*
chemical_list: D002244:Carbon; D009584:Nitrogen
keywords: Community Land Model; Fixation and Uptake of Nitrogen; carbon cost; mycorrhizal fungi; net primary production; nitrogen uptake