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PI-Submitted Research Highlights for
Terrestrial Ecosystem Science Program

Nitrogen Status Regulates Morphological Adaptation of Marsh Plants to Elevated CO2

Pat Megonigal

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September 25, 2019

“Shrinking Stem” response disappears with nitrogen fertilization.

The Science
Most plants are known to grow faster in an elevated carbon dioxide (CO2) atmosphere, provided they have sufficient nitrogen to use in building plant tissues. A new study found that, while this is true when considering the amount of plant growth per unit of ground area (per meter squared), individual plants may shrink in size in some ecosystems. Researchers conducting the study propose that elevated CO2 can cause clonal plants that reproduce from rhizomes to become denser but smaller and that this result has important consequences for how ecosystems function.

The Impact
Tidal marshes are among the most effective ecosystems on Earth for removing CO2 from the atmosphere and burying it in soils. This process contributes to the ability of marshes to tolerate sea level rise because it adds elevation to the soil surface, maintaining flooding frequency within the marshes’ physiologic limits. A numerical model of sediment deposition in tidal marshes indicates that the increase in stem density will contribute to soil elevation gain, a response that will increase the stability of tidal marshes experiencing accelerated sea level rise.

Summary
It is well known that most C3 plants grow faster in an elevated CO2 atmosphere, provided they have sufficient nitrogen, and that growth at elevated CO2 is preferentially invested in roots to support soil nitrogen acquisition. In ecosystems such as grasslands, which are dominated by herbaceous species, the productivity response is usually measured on an area basis without considering whether increased growth is due to larger individual plants, more individuals per area, or both. This research shows that CO2 stimulation of root growth in a clonal plant species increased biomass on an area basis by 20% but decreased the biomass of individual stems by 16%. This “shrinking stem” response was a consequence of a CO2-induced increase in rhizome production as plants foraged for soil nitrogen, and it disappeared when the ecosystem was fertilized with nitrogen. A numerical model of sediment deposition in tidal marshes indicates that the increase in stem density will contribute to soil elevation gain, a response that will increase the stability of tidal marshes experiencing accelerated sea level rise.

Contacts
BER Program Manager
Daniel Stover
U.S. Department of Energy Office of Science, Office of Biological and Environmental Research
Earth and Environmental Systems Sciences Division (SC-33.1)
Environmental System Science
daniel.stover@science.doe.gov

Principal Investigator
Pat Megonigal
Smithsonian Environmental Research Center
Edgewater, MD 21037-0028
megonigalp@si.edu

Funding
This work was supported by the Office of Biological and Environmental Research (Contract No. DE-SC0008339) within the U.S. Department of Energy Office of Science,  the National Science Foundation (NSF) Long Term Research in Environmental Biology (LTREB) program (DEB-0950080 and DEB-1457100), and the Smithsonian Institution.

Publication
Lu, M., E. R. Herbert, J. A. Langley, M. L. Kirwan, and J. P. Megonigal. “Nitrogen status regulates morphological adaptation of marsh plants to elevated CO2.” Nature Climate Change 9,764–68 (2019). [DOI:10.1038/s41558-019-0582-x].

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