Phosphorus Feedbacks May Constrain Tropical Ecosystem Responses to Changes in Atmospheric CO2

Important to consider interactions between carbon, water, and nutrient cycling in predicting future carbon uptake in tropical ecosystems.

The Science

Phosphorus has been generally considered to be the most limiting nutrient in lowland tropical forests. Several recent field studies in the Amazonia have highlighted the importance of phosphorus in tropical forest productivity and function. Despite the importance of phosphorus in tropical carbon cycling, most Earth system models do not currently include phosphorus cycling and phosphorus limitation. This study investigates how phosphorus cycling dynamics might affect tropical ecosystem responses to changes in atmospheric carbon dioxide (CO2) and climate using a phosphorus-enabled land surface model.

The Impact

This study shows that the coupling of phosphorus cycle in land surface model results in more realistic spatial pattern of simulated ecosystem productivity in the Amazon region. Through exploratory simulations, this study points to the need for more tropical field measurements under different temperature and humidity conditions with different soil phosphorus availability.

Summary

It is being increasingly recognized that carbon-nutrient interactions play important roles in regulating terrestrial carbon cycle responses to increasing CO2 in the atmosphere and climate change. Nitrogen-enabled models in CMIP5 showed that accounting for nitrogen greatly reduces the negative feedback between land ecosystems and atmospheric CO2. None of the CMIP5 models has considered phosphorus as a limiting nutrient, although phosphorus has been considered the most limiting nutrient in lowland tropical forests. In this study, scientists from Oak Ridge National Laboratory investigated the effects of phosphorus availability on carbon cycling in the Amazon region using a phosphorus-enabled land surface model. Model simulations demonstrate that the CO2 fertilization effect in the Amazon region may be greatly overestimated if phosphorus cycling were not considered. Exploratory simulations highlighted the importance of considering the interactions between carbon, water, and nutrient cycling (both nitrogen and phosphorus) for the prediction of future carbon uptake in tropical ecosystems.

Principal Investigator

Xiaojuan Yang
Oak Ridge National Laboratory
yangx2@ornl.gov

Program Manager

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

Funding

X. Yang, P.E. Thornton, D.M. Ricciuto, and F.M. Hoffman are supported by the jOffice of Biological and Environmental Research within the U.S. Department of Energy Office of Science, including support from the following programs: Regional and Global Climate Modeling Program [Oak Ridge National Laboratory (ORNL) BGC-Feedbacks Scientific Focus Area (SFA)], Terrestrial Ecosystem Science (TES) program (ORNL TES SFA and Next-Generation Ecosystem Experiments (NGEE)–Tropics project, and Earth System Modeling (ACME project).

References

Yang, X., P. E. Thornton, D. M. Ricciuto, and F. M. Hoffman. "Phosphorus feedbacks constraining tropical ecosystem responses to changes in atmospheric CO2 and climate". Geophysical Research Letters 43 (13), 7205–7214  (2016). https://doi.org/10.1002/2016GL069241.