U.S. Department of Energy Office of Biological and Environmental Research

PI-Submitted Research Highlights for
Terrestrial Ecosystem Science Program

Phosphorus Feedbacks May Constrain Tropical Ecosystem Responses To Changes In Atmospheric CO2

Xiaojuan Yang
Oak Ridge National Lab

Highlight

Figure. Simulated change in land carbon storage in response to historical increase in [CO2] (1900–2009): (top) Vegetation carbon, (middle) soil carbon, and (bottom) total ecosystem carbon based on CNP and CN. Unit: Pg C.

(Figure provided by Author, used in publication)

June 30, 2016

The Science
Phosphorus (P) 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 P in tropical forest productivity and function. Despite the importance of P in tropical carbon cycling, most Earth System Models don’t currently include P cycling and P limitation.  In this study, we investigate how P cycling dynamics might affect tropical ecosystem responses to changes in atmospheric CO2 and climate using a P-enabled land surface model.

The Impact
This study shows that the coupling of P 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/humidity conditions with different soil P 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 P as a limiting nutrient, although P has been considered the most limiting nutrient in lowland tropical forests. In this study, scientists from Oak Ridge National Lab investigated the effects of P availability on carbon cycling in the Amazon region using a P-enabled land surface model. Model simulations demonstrate that CO2 fertilization effect in the Amazon region may be greatly overestimated if P 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.

Contacts (BER PM)
Daniel Stover, Dorothy Koch and Renu Joseph
Daniel.Stover@science.doe.gov (301-903-0289)
dorothy.koch@science.doe.gov (301-903-0105)
renu.joseph@science.doe.gov (301-903-9237)

(PI Contact)
Xiaojuan Yang
Environmental Science Division and Climate Change Science Institute
Oak Ridge National Lab
yangx2@@ornl.gov (865-574-7615)

Funding
X. Yang, P.E. Thornton, D.M. Ricciuto, and F.M. Hoffman are supported by DOE Office of Science, Biological and Environmental Research, including support from the following programs: Regional and Global Climate Modeling Program (ORNL BGC-Feedbacks SFA), Terrestrial Ecosystem Science Program (ORNL TES SFA and NGEE-Tropics), Earth System Modeling (ACME project)  

Publications
Yang, X., P. E. Thornton, D. M. Ricciuto,and F. M. Hoffman (2016), Phosphorus feedbacks constraining tropical ecosystem responses to changes in atmospheric CO2 and climate, Geophys. Res. Let., 43, 7205-7214, doi:10.1002/2016GL069241.

NGEE-Tropics

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