Regulatory effects of non-growing season precipitation on the community structure, biomass allocation, and water-carbon utilization in a temperate desert steppe

Under the influence of global change, precipitation amounts and extreme precipitation frequency during non-growing seasons in mid-high latitude grasslands have been increasing. However, the ecological effects of non-growing season precipitation in the desert steppe have long been overlooked due to an insufficient understanding of the correlative mechanisms linking non-growing season precipitation to plant growth. Therefore, a 3-year non-growing season precipitation manipulation experiment was conducted to reveal the response of desert steppe plants to non-growing season precipitation changes. Our study indicates that, by influencing water budget and availability, non-growing season precipitation directly or indirectly impacted community structure, plant biomass allocation, and water-carbon utilization intensity. Adaptive strategies of communities and plants included: ① Dominant species enhanced their dominance in the community to adapt to non-growing season precipitation changes. ② Stipa krylovii exhibited different biomass allocation strategies in response to non-growing season precipitation variations. Plants in the precipitation shading plots tended to allocate biomass to the roots, while those in the precipitation increase plots favored aboveground development. ③ Persistent drought during the growing season intensified early insufficient development of plants in the precipitation shading plots. Upon entering the wet period, plants in the precipitation shading plots shifted into a compensatory growth mode with high water-carbon activity intensity, while those in the precipitation increase plots entered a moderate growth mode with relatively low water-carbon activity intensity. Additionally, our study found that the regulatory effects of non-growing season precipitation were more pronounced in the growing seasons with less precipitation in the early to middle stage. Moreover, increased non-growing season precipitation enhanced plant water use efficiency (WUE) and strengthened their resilience to drought conditions. Our study suggests that the ecological role of non-growing season precipitation may be further highlighted in the future climate change pattern. Given the worldwide increase in frequency of extreme precipitation events, particular vigilance should be paid to the underlying long-term adverse effects of severe droughts during the non-growing season. Our findings provide new insights and valuable experimental observational evidence for the climate change impact assessment and response in xerophytic grassland ecosystems.