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.

Principal Investigator

Pat Megonigal
Smithsonian Environmental Research Center
megonigalp@si.edu

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
daniel.stover@science.doe.gov

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.

References