November 06, 2017

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Nitrogen Acquisition Efficiency of Plants in Response to Elevated CO2

Ecosystem responses to elevated CO2 governed by plant-soil interactions and the cost of nitrogen acquisition.

The Science

A major determining factor in how a plant acquires nutrients is its associated soil microbial community. In the case of symbiotic mycorrhizal fungi, plants provide the fungi with sugars in exchange for nutrients acquired from soil by the fungi. This exchange is especially important under atmospheric elevated CO2, as plants provision some of the “extra” sugar to promote more nutrient-acquisition by the fungi. In this synthesis, researchers explored how plants from two of the most dominant mycorrhizal groups — arbuscular and ectomycorrhizal fungi — dictate the carbon cost of nitrogen acquisition in an elevated CO2 environment, which may determine ecosystem sensitivity to elevated CO2.

The Impact

Nitrogen is one of the primary limiting factors for plant photosynthesis, which is, in turn, a limiting factor of how much CO2 a plant can uptake from photosynthesis. In a previous synthesis, researchers (Terrer et al. 2016) showed that systems dominated by arbuscular or ectomycorrhizal fungi differed in sensitivity to elevated CO2. This review provides context to those findings, highlighting how other changes in plants under elevated CO2 can have cascading effects. The incorporation of a plant-microbe system, which models dynamic nitrogen acquisition strategies, is more accurate than previous methods that forced fixed nitrogen limitations for land surface models.

Summary

This paper outlines a plant economics framework in which a plant’s efficiency in acquiring nitrogen is measured by the “return on investment” received for the carbon it puts into building roots and fueling soil microbes. Plants are broken into three groups of soil microbe association: arbuscular mycorrhizae (AM, one type of root fungus), ectomycorrhizae (ECM, the other root fungus), and N-fixing bacteria (which retrieve nitrogen from air to give to trees). Researcher found that ECM-associated trees had the best return on investment, meaning that ECM plants received large amounts of nitrogen while putting comparatively less carbon into acquisition. In contrast, AM trees were the least effective at this return on investment. These findings are important information for determining the future of terrestrial ecosystems in an elevated CO2 environment and showcase the importance of soil-microbe association of plants in modeling techniques.

Principal Investigator

Joshua B. Fisher
UCLA, JPL
[email protected]

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
[email protected]

Funding

DOE BER Environmental System Science (formerly Terrestrial Ecosystem Science) program and the NSF Ecosystem Science program.

References

Terrer, C., et al. "Ecosystem Responses to Elevated CO2 Governed by Plant-Soil Interactions and the Cost of Nitrogen Acquisition." New Phytologist 217 (2), 507-522  (2018). https://doi.org/10.1111/nph.14872.

Terrer, C., et al. "Mycorrhizal Association as a Primary Control on the CO2 Fertilization Effect." Science 353 (6294), 72-74  (2016). https://doi.org/10.1126/science.aaf4610.