Effects of an Experimental Drought on Trace Gas Emissions From a Humid Tropical Forest

Tropical forest soils are a major source of radiatively-active trace gases, including carbon dioxide (CO2) and nitrous oxide (N2O). Climate change is likely to alter soil moisture availability in tropical forests, and consequently the magnitude and temporal pattern of trace gas emissions from these systems. In this study, we simulate one of the major future climate scenarios for tropical regions, drought, by excluding three months of wet season throughfall in a humid tropical forest in Puerto Rico. We paired five 1.24 m2 translucent roofs with five control plots of equal size in each of three forest types in the Bisley watershed (Palm, Ridge and Slope; 30 plots total). We measured weekly changes in CO2 and bi-weekly changes in N2O and methane (CH4) in response to the manipulation for each of the 30 plots. We additionally measured the physical and chemical changes associated with throughfall exclusion, including soil nutrient availability, pH and soil temperature. CO2 emissions decreased significantly in the exclusion plots in all three of the forest types. The exclusion effect on CO2 efflux was most pronounced in the sloped sites, followed by the Ridge and the Palm forest sites (32%, 30%, 15%, respectively). The strong negative effect of soil drying on CO2 efflux could mean reduced CO2 emissions from humid tropical forest soils during periods of drought.