Advanced growing-season precipitation peak promotes soil nitrogen mineralization in a semi-arid grassland

Soil nitrogen (N) mineralization is a key process of global N cycling and profoundly regulates plant productivity and soil nutrient pools in the terrestrial biosphere. However, its response to seasonal precipitation redistribution remains largely unexplored. As part of a nine-year (2013–2021) field experiment that simulated advanced and/or delayed growing-season precipitation peaks in a semi-arid grassland on the Mongolian Plateau, this study was conducted for two years (2020–2021) in situ to examine the effects of changing precipitation distributions in the growing seasons on soil mineralization processes. The results showed that advanced precipitation peak (AP) increased soil ammonification (R_amm), nitrification (R_nit), and net mineralization rates (R_min) by 45.8 %, 26.0 %, and 84.4 %, respectively (all p < 0.001), whereas delayed precipitation peak (DP) enhanced R_amm by 55.7 % (p < 0.001) only, but did not change R_nit or R_min. The elevated soil N mineralization under the AP treatment could be primarily attributed to the increased soil water availability and microbial biomass N in the early growing season, both of which play essential roles in meditating biological processes in the soil. In addition, the large consumption of soil inorganic N in the early and middle growing seasons may lead to an enhancement of ammonification in September. These observations suggest that advanced rather than delayed growing-season precipitation peak has a stronger influence on soil N dynamics in the growing seasons. Moreover, our findings highlight the positive contributions of altered N transformations to soil respiration and net ecosystem productivity under the AP treatment and imply the crucial roles of intra-annual redistribution of precipitation in regulating ecosystem nutrient and carbon cycling in semi-arid regions.