Accelerated soil CO2 efflux after conversion from secondary oak forest to pine plantation in southeastern China

Soil respiration (R (s)) is an important component of the carbon cycle in terrestrial ecosystems, and changes in soil respiration with land cover alteration can have important implications for regional carbon balances. In southeastern China (Xiashu Experimental Forest, Jiangsu Province), we used an automated LI-8100 soil CO2 flux system to quantify diurnal variation of soil respiration in a secondary oak forest and a pine plantation. We found that soil respiration in the pine plantation was significantly higher than that in the secondary oak forest. There were similar patterns of soil respiration throughout the day in both the secondary oak forest and the pine plantation during our 7-month study (March-September 2005). The maximum of R (s) occurred between 4:00 pm and 7:00 pm. The diurnal variations of R (s) were usually out of phase with soil surface (0.5 cm) temperature (T (g)). However, annual variation in R (s) correlated with surface soil temperature. Soil respiration reached to a maximum in June, and decreased thereafter. The Q(10) of R (s) in the secondary oak forest was significantly higher than that in the pine plantation. The higher Q(10) value in the secondary oak forest implied that it might release more CO2 than the pine plantation under a global-warming scenario. Our results indicated that land-use change from secondary forest to plantation may cause a significant increase in CO2 emission, and reduce the temperature sensitivity of soil respiration in southeastern China.