关键词: 北方草原, 总氮矿化, 极端降水, 敏感性, 土壤水分

Abstract: Aims： Under the background of global climate change, frequent extreme precipitation events will affect the soil nitrogen transformation process in the semi-arid steppe. However, how the key processes of soil nitrogen transformation respond to precipitation change and the sensitivity of total nitrogen mineralization rate to different precipitation levels remains unclear. Methods： In this study, the gross nitrogen mineralization rate (GNM), and gross nitrification rate (GN) of soil were measured by the 15N pool dilution method based on meadow steppe, typical steppe, and desert steppe of the Global Change Network test platform of northern China Steppe. And related biological (microbial biomass carbon, microbial biomass nitrogen, background biomass (BGB)), and abiotic (soil temperature (ST), soil water content (SWC)) soil substrate (soil ammonium nitrogen (NH4+-N), nitrate nitrogen (NO3--N, soluble organic carbon, soluble organic nitrogen) indexes. Important findings：The results showed that there were significant differences in GNM among different steppe types. The highest GNM was in meadow steppe (3.284 ± 0.613mg·kg-1·d-1), followed with typical steppe (1.370 ± 0.167 mg·kg-1·d-1) and desert steppe (0.724 ± 0.216 mg·kg-1·d-1). However, A 50% decrease in rainfall had no significant effect on GNM and GN of the three grasslands. The sensitivity of GNM and GN to precipitation reduction in typical steppe and desert steppe soil were significantly higher than that of precipitation increase, while the sensitivity of GNM and GN in meadow steppe soil was not significantly different between precipitation increase and decrease. Structural equation model (SEM) analysis revealed that soil moisture was the main factor affecting soil GNM. These results indicate that short-term extreme precipitation has no significant effect on GNM and GN of three important grasslands in northern China, but changes their sensitivity to precipitation change. How the increase of extreme precipitation events will affect the soil nitrogen conversion process in terrestrial ecosystems in the future needs to be systematically studied on long-term scales and large spatial patterns.

Key words: Northern grassland, gross nitrogen mineralization, Extreme precipitation, Sensitivity, Soil moisture