Carbon Cost of Plant Nitrogen Acquisition
How is ecosystem growth and carbon sequestration limited by insufficient nitrogen?
Plants take up carbon from the atmosphere and use that carbon for growth, reproduction, and defenses. Researchers found that plants also use that carbon to acquire nitrogen from various sources—approximately 13 percent of useable carbon (net primary production or NPP) is used for nitrogen acquisition globally (2.4 Pg C yr-1).
Most global terrestrial biosphere models do not include the carbon cost of nitrogen acquisition, thereby failing to represent nitrogen limitation to plant carbon dynamics. Much of the uncertainty in the modeled predictions of the future land carbon sink is driven by how these models prescribe nutrient constraints on primary production. Incorporation of these dynamics into global models will lead to improved changes in climate predictions.
A plant productivity-optimized nutrient acquisition model was integrated into one of the most widely used global terrestrial biosphere models, the Community Land Model (CLM). Global plant nitrogen uptake is dynamically simulated in the coupled model based on the carbon costs of nitrogen acquisition from mycorrhizal roots, non-mycorrhizal roots, symbiotic nitrogen-fixing microbes, and remobilization of nutrients from senescing leaves. Mycorrhizal uptake represented the dominant pathway by which nitrogen is acquired, accounting for about 66 percent of the nitrogen uptake by plants. Overall, the coupled model improves the representations of plant growth limitations globally. Such model improvements are critical for predicting how plant responses to altered nitrogen availability (from nitrogen deposition, rising atmospheric carbon dioxide, and warming temperatures) may impact the land carbon sink.
University of California, Los Angeles; Jet Propulsion Laboratory
Funding was provided by the U.S. Department of Energy, Office of Biological and Environmental Research, Terrestrial Ecosystem Science Program; and the U.S. National Science Foundation’s Ecosystem Science Program.
Shi, M., J. B. Fisher, E. R. Brzostek, and R. P. Phillips. 2016. “Carbon Cost of Plant Nitrogen Acquisition: Global Carbon Cycle Impact from an Improved Plant Nitrogen Cycle in the Community Land Model,” Global Change Biology 22(3), 1299-1314. DOI: 10.1111/gcb.13131.