降水量及N添加对宁夏荒漠草原土壤C:N:P生态化学计量特征和植被群落组成的影响

为了解降水格局改变和大气氮(N)沉降增加背景下土壤碳(C)∶N∶磷(P)平衡关系的改变是否会影响到荒漠草原植被群落组成, 基于2017年在宁夏荒漠草原设立的降水量(降水量减少50%、降水量减少30%、自然降水量、降水量增加30%和降水量增加50%)、N添加(0和5 g·m^-2·yr^-1)及其交互作用的野外试验, 初步分析了土壤C∶N∶P生态化学计量特征和植物群落组成的变化趋势以及二者的关系。结果表明, 增加降水量降低了土壤有机C、全N和N∶P。N添加及其与降水量的交互作用对土壤C∶N∶P生态化学计量特征的影响较小; 适量增加降水量刺激了多数植物生长, 提高了群落多样性。过量增加降水量导致猪毛蒿种群生物量急增, 且N添加对降水量效应有促进作用, 从而降低了群落多样性; 土壤含水量、全N、有机C和N∶P与种群生物量关系较为密切, 土壤含水量、有机C、C∶P和C∶N与多样性指数存在较强的相关关系。以上结果意味着降水量会通过调控土壤水分有效性, 改变土壤与植物之间N和P的满足程度, 从而对植物生长策略和群落多样性产生影响; 短期N添加对土壤养分有效性影响较小。因此, 还需通过长期的原位试验, 对N添加及其与降水量交互作用下土壤C∶N∶P计量平衡与植物群落组成的关系进行深入探讨。

Effects of precipitation and N addition on soil C∶N∶P ecological stoichiometry and plant community composition in a desert steppe of Ningxia,northwestern China

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.