Monday, August 4, 2008

PS 3-60: Daily and seasonal patterns in soil CO2 efflux at different aged plantations of Chinese fir in southern China

Dalun Tian1, Wende Yan1, Yuanying Peng2, Xiaoyong Chen3, Changhui Peng4, Wenhua Xiang1, and Xiangwen Deng1. (1) Forest Ecology Section, Faculty of Life Science, Central South University of Forestry and Technology, (2) College of DuPage, (3) Governors State University, (4) University of Quebec at Montreal

Background/Question/Methods

Soil carbon dioxide efflux (FCO2) plays a critical role in the carbon cycling of forest ecosystems because it may contribute as much as 60–80% of total respiration in the ecosystems. We measured the soil FCO2 of Chinese fir plantations with three age classes: 5–year-old (young), 12-year-old (middle age), and 20-year-old (mature age) for the entire year of 2006 in Hunan province, China. Soil temperature (Tsoil,), moisture (Wg), pH, depth to bedrock, and organic matter contents were also measured. The specific objectives of the study were (1) to quantify daily and seasonal patterns of soil FCO2 in Chinese fir plantation at various growth and development stages; (2) to determine if the different-aged Chinese fir stands affect soil FCO2; and (3) to examine relationships between soil FCO2 and relevant soil properties among forest age classes.

Results/Conclusions

The results indicated that the rate of soil FCO2 was decreased with the increases of forest ages. Annual averaging soil FCO2 was 1.20, 1.13 and 0.85 μmol m-2 s-1 in young, mid-age and mature stands, respectively. The measured CO2 fluxes ranged from 0.20-0.35 µmol.m-2.s-1 in January to 1.60-2.85 µmol m-2 s-1 in July for the three aged stands. A significant seasonal pattern of soil FCO2 was found in the three ages of the plantations with a peak value occurring in July and the lowest values appearing in January. The daily patterns of soil FCO2 showed that the highest value was appeared around while the lowest value occurred at the early morning about 4:00 am for three age classes. FCO2 was strongly correlated with Tsoil, but not for Wg. The significant nonlinear relationship between FCO2 and Tsoil was described using an exponential function (r2 at 0.81 and Q10 at 2.6) for all three aged forests. It was found that soil depth to bedrock had a strong effect was on soil FCO2; however, Wg, soil pH and soil organic matter concentration had no detectable effects. Our results suggested that the influences of various aged stands on soil FCO2 was mainly attributed to the changes in both forest canopy density and root systems in the Chinese fir plantations.