Soil respiration in a natural forest and a plantation during a dry period in the Philippines

Climate change is forecast to increase the frequency of extreme hot temperatures and dryer days and is anticipated to have profound impacts on the global carbon budget. Droughts are expected to alter soil respiration (R-s) rates, but the scarcity of data preclude a reliable estimate of this response and its future trajectory. A field experiment using an automated soil respiration machinery (LI-8100A) was conducted in a natural forest and a plantation during a dry period in the Philippines, with the goal of quantifying R-s rates and their relationship with soil temperature and moisture, and air temperature. The natural forest (5.81 & mu;mol m(-2) s(-1)) exhibited significantly higher R-s rates (p < 0.0001) compared with the plantation (1.82 & mu;mol m(-2) s(-1)) and control (3.23 & mu;mol m(-2) s(-1)). R-s rates showed significant negative relationships with air (- 0.71) and soil temperatures (- 0.62), indicating that as temperatures increase, the R-s rates decrease. In contrast, the R-s rates exhibited a significant positive relationship with soil moisture (0.65). Although the low R-s rates in the plantation and high R-s rates in the natural forest are indicators of sensitivities of these two types of tropical forests to warm, dry soil, this observation is only conclusive during the dry period, but not necessarily during wet periods. Further studies are needed to determine the trend of R-s rates during wet periods, considering different site conditions and types of vegetation.