The Effects of Phosphorus Cycle Dynamics on Carbon Sources and Sinks in the Amazon Region: A Modeling Study Using ELM v1
ELM v1 is able to capture the observed west-to-east gradient of productivity and biomass because of the introduction of phosphorus (P) cycle dynamics and soil order-based tree mortality. Our model simulations show that the consideration of P availability leads to a smaller carbon sink associated with CO2fertilization effect, and lower carbon emissions due to land use and land cover change (LULCC). Our simulations suggest P limitation would significantly reduce the carbon sink associated with CO2fertilization effects through the twenty-first century.
Recent climate models suggested that the Amazon carbon sink is resilient mainly due to the CO2fertilization effect. Our study suggests that the projected carbon sink would become much smaller when phosphorus limitation is considered. Combined with the possible decrease of the area of intact tropical forests that act currently as carbon sink and increasing ecosystem respiration with climate change, the Amazon region may become a source of carbon in the future.
P cycle dynamics and C-N-P interactions have been implemented into the Energy Exascale Earth System Model (E3SM) land model (ELM v1), which allows ELM v1 to capture the observed spatial gradient of productivity across the Amazon region. Historical simulations suggest that the consideration of P availability leads to a smaller carbon sink associated with CO2fertilization effect, and lower carbon emissions due to land use and land cover change (LULCC). When all environmental factors are considered, our model simulations show a smaller carbon sink in the Amazon region when P limitation is considered. Our simulations with CO2concentrations from RCP8.5 and RCP4.5 suggest that P limitation is critical for projecting future carbon uptake in tropical ecosystems. The predicted carbon sink in Amazon rainforests would be much smaller when P limitation is considered, suggesting that the Amazon tropical forests may offer less protection against future climate change than suggested by previous modeling studies.