Effects of land use and precipitation on above- and below-ground litter decomposition in a semi-arid temperate steppe in Inner Mongolia, China

•Litter inputs, quality and decomposition rates differed greatly among the land-use types.•Precipitation is a primary constraint on grass ecosystem C processes.•Above-ground litter decomposed faster than root litter among land-use types.•Above-ground litter decomposition was explained best by the initial N content and C/N ratio.•Root litter decomposition was explained best by the initial C/N ratio.

Land use greatly affects litter production, quality, and decomposition rates, and therefore alters the soil carbon stocks and influences ecosystem carbon cycling. In this study, our aims were to investigate the effects of land use (grazing, mowing, and grazing exclusion), litter types, and precipitation on litter production, decomposition processes, and soil carbon stocks. Litter inputs, quality, and decomposition rates were significantly influenced by land use and differed greatly between 2011 (a dry year) and 2012 (a moist year). Above-ground litter production in 2012 ranged from 165 to 180 g m−2, versus from 50 to 73 g m−2 in 2011; below-ground litter production in 2012 was 1.9 to 6.0 times that in 2011. Decomposition rates of above-ground litter (ka) were greater than those of below-ground litter (kb). The ka in 2012 was 1.9 to 2.8 times those in 2011 and kb in 2012 was 6.5 to 10.8 times those in 2011. The ka was strongly positively correlated with the N content (R2 = 0.713) and strongly negatively correlated with the C/N ratio (R2 = 0.585), whereas kb was explained best by the C/N ratio. Precipitation was a main factor that controlled ecosystem C cycling processes, and increased litter decomposition increased soil carbon stocks. Land use therefore played an important role in litter input and decomposition processes and in carbon sequestration, but these processes responded to the initial litter quality and precipitation.