Relationships among Soil Properties, CO2 Emission and Ecosystem Respiration in Dry Dipterocarp Forest, Western Thailand

CO2 emissions from the forest (ecosystem respiration, Re) come from both aboveground respiration (plant respiration, Ra) and belowground respiration (soil respiration, Rs). The ratio between Re and Rs varies in time and space. It is not well understood especially in the tropical forests that how these two components play the roles in controlling the amount of CO2 emissions, and how they respond to the changes in environmental factors such as precipitation, soil moisture and temperature. Understanding the responses to such environmental factors is fundamental to an accurate prediction of the impacts of climate on carbon cycling processes, i.e. on sources or sink capacity and climate feedbacks. The objectives of the present study are to quantify the contribution of Rs to Re, and to investigate the relationship between soil properties and CO2 release in a dry dipterocarp forest in western Thailand. It was found that the averaged soil respiration (Rs) in 2009 and 2010 were 459.10±162.67 and 404.28±133.31 mgCO2mhr, respectively. The averaged ecosystem respiration rates during these same years were 497.30±336.12 and 686.32±416.04 mgCO2mhr, respectively. Annual estimates of soil and ecosystem respiration indicate that the annual Rs/Re ratio ranged from 0.24-1.20, with a mean of 0.57. Rs/Re ratio was relatively high in dry season [0.91, during November to April] when compared with during wet season [0.55, during May to October].The relatively high contribution of Rs to Re is quite unique for this dry dipterocarp forest. Comparing the amount of CO2 respired during wet and dry seasons, 80% was released during the wet season (April-November) when the monthly average of soil moisture content was above 8% WFPS. High contribution of Rs to Re during dry season was due to the low aboveground respiration associated with leaf fall in the periods. Analyzing the relationship between soil respiration and ecosystem respiration with soil property factors indicates that unlike in temperate forest, tropical dry dipterocarp forest shows decreasing respiration when soil temperature increases. However, positive correlation between soil respiration and soil moisture was found in both wet and dry seasons. __________________ 1) Graduate Student 2) Professor