Effects of Moisture and Temperature on Respiration in Tropical Forest and Agricultural Soils

Abstract

Soil respiration in tropical uplands was studied in agriculture (maize) and dry evergreen forest soils. The objective of this study was to investigate the effects of moisture and temperature on soil respiration. Diurnal variations of in situ soil CO₂ efflux was studied in May 2004 and February 2005.
In the laboratory, soil respiration in a short-term incubation was measured under various moisture contents (air-dry, 25, 50, 75 and 100%WHC) and various constant temperatures (10°C to 45°C). In situ soil CO₂ flux showed strong diurnal patterns correlated with both air and soil temperature. CO₂ efflux from both study sites increased to the maximum values during the late afternoon, usually 2-4 hours after a peak in air temperature. The total soil CO2 fluxes integrated over the measurement period were 1354 and 3082 mg CO₂ m^-2 day^-1 at agricultural site and 1467 and 12851 mg CO₂ m^-2 day^-1 at forest site in May 2004 and February 2005, respectively. The Q10 value for agricultural site estimated from relationship between soil temperature at 5 cm and CO2 flux was 3.37 (May 2004). For the forest site, the Q10 was 2.04 (February 2005). Results from laboratory study indicated that the topsoil layer (the top 20 cm) contributed mainly to the overall respiration. Soil respiration was highest at moisture between 50% and 75% WHC. The Q10 values of agricultural soil were higher than of that of the forest soil, indicating relatively higher sensitivity of the agricultural soil to temperature change than the forest soil. Laboratory results also indicated that subsoil was more sensitive to temperature and moisture changes than topsoil.