Page Comparison

Abstract

Tropical forests play a crucial role in the global carbon cycle, accounting for one third of the global NPP and containing about 25% of global vegetation biomass and soil carbon.  This is particularly true for tropical forests in the Amazon region, as it comprises approximately 50% of the world’s tropical forests.  It is therefore important for us to understand and represent the processes that determine the fluxes and storage of carbon in these forests. In this study, we show that the implementation of phosphorus (P) cycle and P limitation in E3SM land model (ELM v1) improves simulated spatial pattern of NPP. The P-enabled ELM-v1 is able to capture the west-to-east gradient of productivity, consistent with field observations.  We also show that by improving the representation of mortality processes, ELMv1 is able to reproduce the observed spatial pattern of above ground biomass.  Our model simulations show that the consideration of P availability leads to a smaller carbon sink associated with CO2 fertilization effect, and lower carbon emissions due to land use and land cover change (LULCC).  Our study suggests that terrestrial ecosystems in the Amazon region make an approximately neutral contribution to the global carbon cycle in recent decades, with the carbon sink associated with increasing atmospheric CO2 roughly cancelled out by the carbon emission associated with LULCC. Our study has important implications for projections of future carbon balance in this region. P limitation could become increasing important in the Amazon region as more P is immobilized into vegetation and SOM, which would constrain productivity stimulated by increasing [CO2] and lead to a source of carbon in the Amazon region.  

...