关键词: 干旱半干旱区, 降水格局改变, 大气N沉降增加, 植物群落多样性, 土壤C:N:P

Abstract: Change in precipitation pattern and increase in atmospheric nitrogen (N) deposition are two important consequences of global change. Soil carbon (C)∶N∶phosphorus (P) ecological stoichiometry could reflect soil organic C level and N and P supply and thus would be closely related to plant growth. Previous studies have reported that both of the changes in precipitation and N deposition may lead to the decoupling of soil C∶N∶P ecological stoichiometry. In order to better understand whether the changes in soil C∶N∶P ecological stoichiometry could affect plant community composition under changing precipitation regimes and increasing atmospheric N deposition, we conducted a field experiment in a desert steppe of Ningxia, northwestern China, involving five precipitation treatments (50% reduction in precipitation, 30% reduction in precipitation, natural precipitation, 30% increase in precipitation, and 50% increase in precipitation) and two N addition treatments (0 and 5 g·m^-2·yr^-1) in 2017, and primarily explored the changes in both soil C∶N∶P ecological stoichiometry and plant community composition and their relationships in August, 2018. It was found that increased precipitation led to decreases in soil organic C, total N, and N∶P, whereas N addition and its interaction with precipitation had little influences on soil C∶N∶P ecological stoichiometry; a moderate increase in precipitation stimulated the growth of most plants and thus increased community diversity. An excessive increase in precipitation resulted in a sharp increase of Artemisia scoparia biomass, combined with the positive effects of N addition, resulting in a reduction of community diversity. To a certain extent, soil water content, total N, organic C, and N∶P were closely related to plant population biomass, while soil water content, organic C, C∶P, and C∶N had closer relationships with diversity indices. Taken together, the results above indicate that precipitation could change N and P relationships between soil supply and plant demand through regulating soil water availability, thus changing plant growth strategy and community diversity; short-term N addition had little effect on soil nutrient availability, consequently, a long-term in situ experiment is needed to further explore mechanisms influencing soil C∶N∶P stoichiometric balance effects on plant community composition under N addition and the interaction between these effects and precipitation change.

Key words: arid and semi-arid regions, changing precipitation regimes, increasing atmospheric N deposition, plant community diversity, soil C∶N∶P;