Tuesday, August 4, 2009: 8:40 AM
Santa Ana, Albuquerque Convention Center
Background/Question/Methods
Tropical forest soils are a globally important source of carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) to the atmosphere. The production and emission of these greenhouse gases is tightly coupled with the amount and distribution of rainfall and associated redox dynamics. Current models predict increasing frequency and severity of drought in many humid tropical regions. These climate changes are likely to feedback on soil moisture availability in humid tropical forests, and consequently on the magnitude and temporal pattern of trace gas efflux from these systems. In this study, we created an experimental drought in a humid tropical forest in Puerto Rico by excluding three months of wet season throughfall. 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 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.
Results/Conclusions
CO2 emissions decreased significantly in response to soil drying in all forest types. The decrease in CO2 efflux was most pronounced in the Slope site, followed by the Ridge and the Palm forest sites (32%, 30%, 15%, respectively). The response of CO2 to declining soil moisture was linear in both the Palm and Ridge sites, and non-linear in the Slope site. Surprisingly, CO2 fluxes remained suppressed in both the Ridge and Slope sites several weeks after the exclusion shelters were removed, while the Palm forest demonstrated a very rapid recovery. The effect of throughfall exclusion on CH4 and N2O emissions varied by forest type. The Palm forest became a strong sink for CH4, and went from a source to a sink of N2O. In contrast, CH4 and N2O did not respond to soil drying in either the Slope or the Ridge sites. Overall, the reduction in trace gas emissions from tropical forest soils in response to drought has significant implications for global carbon and nitrogen cycling if climatic change continues to follow current trends.
Tropical forest soils are a globally important source of carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) to the atmosphere. The production and emission of these greenhouse gases is tightly coupled with the amount and distribution of rainfall and associated redox dynamics. Current models predict increasing frequency and severity of drought in many humid tropical regions. These climate changes are likely to feedback on soil moisture availability in humid tropical forests, and consequently on the magnitude and temporal pattern of trace gas efflux from these systems. In this study, we created an experimental drought in a humid tropical forest in Puerto Rico by excluding three months of wet season throughfall. 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 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.
Results/Conclusions
CO2 emissions decreased significantly in response to soil drying in all forest types. The decrease in CO2 efflux was most pronounced in the Slope site, followed by the Ridge and the Palm forest sites (32%, 30%, 15%, respectively). The response of CO2 to declining soil moisture was linear in both the Palm and Ridge sites, and non-linear in the Slope site. Surprisingly, CO2 fluxes remained suppressed in both the Ridge and Slope sites several weeks after the exclusion shelters were removed, while the Palm forest demonstrated a very rapid recovery. The effect of throughfall exclusion on CH4 and N2O emissions varied by forest type. The Palm forest became a strong sink for CH4, and went from a source to a sink of N2O. In contrast, CH4 and N2O did not respond to soil drying in either the Slope or the Ridge sites. Overall, the reduction in trace gas emissions from tropical forest soils in response to drought has significant implications for global carbon and nitrogen cycling if climatic change continues to follow current trends.
