Effect of enclosure on soil C mineralization and priming effect in stipa grandis grassland of inner mongolia

Abstract

In recent decades, the carbon (C) cycle and soil respiration of terrestrial ecosystems have been become hot topics for the global climate change, and research focused on the temperature sensitivity and priming effects of soil microbial respiration (or soil C mineralization) has increased rapidly since 2000. In this study, we focused on long-term fenced Stipa grandis grassland (FG) and grazing Stipa grandis grassland (GG) in Inner Mongolia, China, investigating the impact of land-use change on the temperature sensitivity and the priming effects of soil microbial respiration by incubating soils in the laboratory under a temperature gradient (5, 10, 15, 20, 25 and 30°C) and with substrate addition (mixed litter). The incubation experiment was continued for 6 weeks, and the rates of soil C mineralization were measured throughout using our newly developed equipment. The results showed that the amount of soil C mineralization was higher in GG than that in FG duration the 6-weeks incubation. The rates of soil C mineralization increased significantly with increasing incubation temperature for both GG and FG (temperature coefficient (Q10) values ranged from 1. 1 to 1. 9), however, the Q10 values for GG and FG were not significantly different. After mixed-litter addition, the rates of soil C mineralization not only in GG but also in FG increased significantly, and showed the apparent "priming effects"of C mineralization. Compared with long- term fenced grassland (FG), grazing grassland (GG) had higher priming effects, which even after only 7 d were 6. 38 times higher. Moreover, the priming effects increased with increasing incubation temperature in the first week, although these effects were the highest at 15°C duration the 42 d of incubation. These findings suggest that, on a longer time scale, medium temperatures should promote soil C mineralization. On the whole, long-term grazing exclusion depressed the priming effect of soil microbial respiration and resulted in less C emission under the same mixed litter input. This is probably one of the mechanisms underlying the capacity of long-term fenced grasslands to sequester CO2 in Inner Mongolia.