Soil Microbial Growth Strategies And Soil Carbon Mineralization In A Chinese Fir Plantation And An Evergreen Broadleaved Forest

The mechanisms of soil organic carbon (SOC) decomposition and its temperature sensitivity, as one of the research hotspot, are important to predict future trends both in terrestrial carbon dynamic and global climate change. Although soil microbes are the main driver of SOC decomposition, their community properties have hardly been clearly linked to their ecological functions, especially to SOC decomposition. In this thesis, we used two methods, viz.(1) Kinetics of substrate-induced respiration, and (2) Kinetics of the modified Michaelis-Monod to study soil microbial growth strategies and soil carbon mineralization in an evergreen broadleaved forest and a Chinese fir plantation in Wanmulin Nature Reserve, China. Firstly, we estimated differences of soil carbon availability, the temperature sensitivity of SOC decomposition, as well as soil microbial growth strategies in topsoil (0-10cm) and subsoil (40-60cm) of Chinese fir and evergreen broadleaved forests. Secondly, we studied soil microbial growth strategies and temperature sensitivity of soil respiration in spring and autumn. Thirdly, we analysed the effect of the ground litter addition. The major results are summarized as follows.(1) Soil carbon availability, the temperature sensitivity of SOC decomposition, as well as soil microbial growth strategies differed between topsoil (0-10cm) and subsoil(40-60cm) for both evergreen broad-leaved forest and Chinese fir plantation. Compared to topsoil, soil carbon availability was higher in subsoil of the two forests, while the temperature sensitivity of SOC decomposition was lower in the subsoils. Soil microbial community in the topsoils of both forests tended to K-strategy features, whereas r-strategy features were dominated in the subsoils. With increasing incubation time, the temperature sensitivity of SOC decomposition increased in both stands, and soil microbial tended more to r strategy.(2)There were differences in soil available C and soil microbial growth strategies between seasons for both stands. The available C was lower in spring than in autumn, and soil microbial community tended to K-strategy in spring. Different seasons influenced soil microbial maintain respiration and growth respiration significantly. Compared to r-strategists, K-strategists had higher temperature sensitivity of growth respiration and lower sensitivity temperature of maintain respiration.(3) Positive priming effect of litter addition on SOC decomposition was not found after3months, while8months later, positive priming effect produced. Soil microbial community structure was affected by litter addition. Soil microbial community tended to r-strategy features after litter addition for3months, while soil microbial tended to K-strategy features after litter addition for8months.This study showed that studying on soil microbial growth strategies related to soil carbon availability, organic carbon mineralization and its temperature sensitivity, can promote our understanding of the mechanism of microbial regulating soil organic carbon dynamics.