Soil carbon release enhanced by increased tropical forest litterfall

Tropical forests are a critical component of the global carbon cycle(1) and their response to environmental change will play a key role in determining future concentrations of atmospheric carbon dioxide (CO2)(1,2). Increasing primary productivity in tropical forests over recent decades has been attributed to CO2 fertilization(3), and greater biomass in tropical forests could represent a substantial sink for carbon in the future(3,4). However, the carbon sequestration capacity of tropical forest soils is uncertain and feedbacks between increased plant productivity and soil carbon dynamics remain unexplored(5,6). Here, we show that experimentally increasing litterfall in a lowland tropical forest enhanced carbon release from the soil. Using a large-scale litter manipulation experiment combined with carbon isotope measurements, we found that the efflux of CO2 derived from soil organic carbon was significantly increased by litter addition. Furthermore, this effect was sustained over several years. We predict that a future increase in litterfall of 30% with an increase in atmospheric CO2 concentrations of 150 ppm could release about 0.6 t C ha(-1) yr(-1) from the soil, partially offsetting predicted net gains in carbon storage. Thus, it is essential that plant-soil feedbacks are taken into account in predictions of the carbon sequestration potential of tropical forests.