Effects of prescribed fire on carbon sequestration of long-term grazing-excluded grasslands in Inner Mongolia

Natural and prescribed fires are common in the typical temperate grasslands in Inner Mongolia and are considered to have a significant impact on the terrestrial ecosystems and even on regional carbon (C) balance because they profoundly alter the biota, land cover, and biogeochemical cycles. Natural and prescribed fires may play important roles and increase the uncertainty in the evaluation of C sequestration in the long-term grazing-excluded grasslands in this region. By conducting a field fire experiment at 4 different frequencies (no burning, and burning every 1, 2, and 4 years) and measuring the C and nitrogen (N) storage in both soil and soil particle-size fractions, researchers have investigated the effects of fire and fire regimes on soil C and N storage in the long-term grazing-excluded grasslands in Inner Mongolia, China. Understanding the effects of fire on soil C storage would help us scientifically evaluate C sequestration of long-term fenced grasslands under different fire regimes in the future. The results of the 4-year prescribed fire experiment showed that fire treatment significantly decreased C storage in the 0- to 30cm soil layer in the approximately 30yearfenced grassland, particularly under frequent fire perturbation. Moreover, the influence of prescribed fire was more apparent in the 0 to 10cm soil layer than in the 10 to 30cm layer. We also found that prescribed fire had an apparent influence on soil organic C in different soil particlesize fractions; the decline of C storage in the sand fraction was higher than that in the silt and silt fractions, indicating that prescribed fire redistributed the organic C in the sand, silt, and clay fractions and significantly affected the stability of soil organic matter (SOM). Compared to freegrazing grasslands outside the fences, long-term fenced grasslands of northern China were found to have tremendous capacity to sequester C in soil, even when these were subjected to different fire regimes. To summarize, fire and fire regimes have significant effect on C storage in soil and soil fractions in these long-term grazingexcluded grasslands in Inner Mongolia; frequent fire significantly decreased soil C storage, and lowfrequency fire (burning every 4 years) decreased soil C storage to a lesser extent. Importantly, the stability of SOM in the surface layer was enhanced after burning in view of the decrease in the C: N ratio in the sand and silt fractions. Compared to the unburned grasslands, the grass