Simulated drought reduces soil CO 2 efflux and production in a tropical forest in Sulawesi, Indonesia

Abstract

Climate models predict that the frequency and intensity of ENSO-related droughts will increase in Southeast Asia, yet little is known about how changes in precipitation patterns will affect soil CO2 efflux. Our objective was to determine drought responses on soil CO2 efflux, CO2 production sources (leaf litter, belowground heterotrophic (microbial) and autotrophic (root) respiration), and on CO2 production within the top 250 cm of soil. We simulated drought conditions in a sub-montane forest in Indonesia by constructing large throughfall displacement roofs in three 40 × 40 m plots and compared measurements with three control plots. The study lasted for 31 months with biweekly measurements: 2.5 months pre-treatment, 9 months of 50% roof closure followed by 15.5 months of 80% closure (46 ± 13% and 80 ± 12% throughfall reductions, respectively), and 4 months of roof opening. Soil CO2 efflux from the control plots was 11.7 ± 1.1 Mg C·ha−1·yr−1 and the contributions from leaf litter respiration, belowground heterotrophic respiration and autotrophic respiration were 29 ± 4%, 45 ± 6% and 30 ± 3%, respectively. Carbon dioxide production in the top 50 cm contributed 65% of the total production within 250 cm. During the simulated drought, soil CO2 efflux declined by 23% in the first 9 months and 48% in the next 15.5 months compared to the control. This was accompanied by significant decreases in both autotrophic and heterotrophic sources. Following roof opening, soil CO2 efflux rebounded slowly, but did not surpass the control. Soil matric potential exhibited an exponential relationship with soil CO2 efflux. The strong drought-induced decrease in soil respiration indicates that this forest ecosystem is drought sensitive, but could recover with commencement of normal rainfall levels.