The role of the phosphorus cycle in tropical ecosystem responses to changes in atmospheric CO2 and climate

Background/Question/Methods

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 indicated that the inclusion of nitrogen cycle reduces CO₂ fertilization effect and warming-induced carbon loss from land ecosystems. None of the CMIP5 models has considered phosphorus (P) as a limiting nutrient, although P has been commonly considered to be the most limiting nutrient in highly productive lowland tropical forests. 

In this study, we focus on investigating the role of phosphorus cycling dynamics in affecting tropical carbon responses to changes in atmospheric CO2 and climate. Model sensitivity experiments have also been performed to better understand which P cycle parameters have the greatest effect in controlling the extent of P limitation in the context of global change. We do this using a recently developed P-enabled land surface model CLM-CNP.

Results/Conclusions

Model simulations show that inclusion of phosphorus coupling leads to a smaller CO₂ fertilization effect and warming-induced CO₂ release from tropical ecosystems. Simulations also show that phosphorus cycle dynamics tend to reduce the sensitivity of NEE to interannual variation in temperature and precipitation. Sensitivity analysis helps us understand the relative importance of P cycle parameters in determining P availability and the extent of P limitation in response to changes in CO2 and climate.