Temperature and substrate availability regulate soil respiration in the tropical mountain rainforests, Hainan Island, China

Tropical forest plays a key role in global C cycle; however, there are few studies on the C budget in the tropical rainforests in Asia. This study aims to (i) reveal the seasonal patterns of total soil respiration (R-T), litter respiration (R-L) and soil respiration without surface organic litter (R-NL) in the primary and secondary Asian tropical mountain rainforests and (ii) quantify the effects of soil temperature, soil moisture and substrate availability on soil respiration. The seasonal dynamics of soil CO2 efflux was measured by an automatic chamber system (Li-8100), within the primary and secondary tropical mountain rainforests located at the Jianfengling National Reserve in Hainan Island, China. The litter removal treatment was used to assess the contribution of litter to belowground CO2 production. The annual R-T was higher in the primary forest (16.730.87 Mg C ha(1)) than in the secondary forest (15.100.26 Mg C ha(1)). The rates of R-T, R-NL and R-L were all significantly higher in the hot and wet season (MayOctober) than those in the cool and dry season (NovemberApril). Soil temperature at 5cm depth could explain 5561% of the seasonal variation in R-T, and the temperature sensitivity index (Q(10)) ranked by R-L (Q(10) 3.39) > R-T (2.17) > R-NL (1.76) in the primary forest and by R-L (4.31) > R-T (1.86) > R-NL (1.58) in the secondary forest. The contribution of R-L to R-T was 2223%, while litter input and R-T had 1 month time lag. In addition, the seasonal variation of R-T was mainly determined by soil temperature and substrate availability. Our findings suggested that global warming and increased substrate availability are likely to cause considerable losses of soil C in the tropical forests.