Responses of soil carbon dynamics to precipitation and land use in an Inner Mongolian grassland

Background and aims: Grasslands hold one of the most important soil carbon stocks in the world, which is vulnerable to climate change (i.e. precipitation) and human disturbance (i.e. land-use). This study aimed to investigate responses and mechanisms of soil organic carbon (SOC) decomposition and accumulation to precipitation and land-use in an Inner Mongolian grassland. Methods: Using a randomized complete block design with a split plot, an experiment with land-use regimes (fencing, grazing, and mowing, since 2011) and altered precipitation amount (wet, + 50% precipitation; CT, ambient precipitation; dry, −50% precipitation; since 2016) was conducted to explore their impacts on SOC decomposition (represented by soil heterotrophic respiration and extracellular enzyme activities) and accumulation (represented by SOC and its physical fractions) from samples collected in 2019. Results: SOC decomposition significantly increased under wet treatment, but decreased under dry treatment. Wet treatment increased SOC accumulation via the increment of mineral-associated organic carbon (MAOC), and vice versa for dry treatment. Precipitation amount may affect soil microbial biomass and activities via alterations of water supply, plant-derived carbon input, and other soil properties, leading to changes of SOC dynamics. Nevertheless, land-use regimes had little influences on SOC dynamics. Conclusions: Compared to land-use regimes, precipitation treatments can significantly change SOC dynamics. Overall, SOC increased under higher precipitation amount, but decreased with less precipitation. We emphasize that the SOC stock in Inner Mongolia temperate grassland may have an unexpectable fast response to precipitation alteration, but more investigation is still needed in longer terms.