Contribution of Soil CO2 flux to Ecosystem Respiration in Dry Dipterocarp Forest, Western Thailand

Differences in rates of net ecosystem carbon sequestration (NEE) between sites and years have been attributed in large part to variation in rates of ecosystem respiration (Re). This in turn varies on the ratios between plant and soil respiration (Rs). However, the research on temporal variations of these ratios across seasons and forest types are quite scare. Studies in the past, indicate that the Rs/Re ratio might vary seasonally, and that understanding this could provide insight into ecosystem responses to varying weather and climate. Soil respiration at the dry dipterocarp forest site in Thailand was measured hourly and continuously by automated-closed chamber method. High contribution of Rs to Re during dry season was due to the low aboveground respiration associated with leaf fall during that periods. Analyzing the relationship between soil respiration and ecosystem respiration with environmental factors, the results indicated that unlike in temperate forest, a dry dipterocarp forest shows decreasing respiration when soil temperature is increasing, and no difference between wet and dry season was found. However, a positive correlation between soil moisture and either Re or Rs was found. The negative response of soil respiration may imply that carbon uptake and release in this forest is operated at the upper temperature limits.