Final Activity Report Summary - GLIMPCARBON (Tropical forest soils and climate change: A source or sink for atmospheric carbon?) Despite the important role of tropical forest soils in the global carbon cycle, estimates of how much carbon can be sequestered by tropical forests are based mostly on measurements of aboveground tree growth because little is known about carbon cycling in the soil and how it may be affected by climate change. Growth in some tropical forests has increased during recent decades, prompting speculation that this will boost carbon sequestration. However, greater amounts of carbon in dead plant material (in particular leaf litter) may accelerate the decomposition of more stable carbon in stored in the soil, which would greatly reduce the value of tropical forests as a carbon sink. Improved understanding of the belowground carbon cycle and how it interacts with aboveground processes is required to accurately estimate the carbon sequestration potential of tropical forest ecosystems.This project combined litter addition, litter removal, and root exclusion treatments to quantify how much plant roots and decomposing leaf litter contribute to carbon dioxide production in a tropical forest. The results of the project demonstrate that changes in aboveground growth will affect soil microorganisms, the quantity of fine root in the soil and the relative proportions of carbon dioxide being produced by roots, decomposing litter and soil carbon. This may ultimately cause losses of carbon dioxide from the soil.