Changes in precipitation can influence soil water and nutrient availability,and thus affect plant nutrient conservation strategies. Better understanding of how nutrient conservation changes with variations in water availability is crucial for predicting the potential influence of global climate change on plant nutrient-use strategy. Here,green-leaf nitrogen (N) and phosphorus (P) concentrations,N-and P-resorption proficiency (the terminal N and P concentration in senescent leaves,NRP and PRP,respectively),and N-and P-resorption efficiency (the proportional N and P withdrawn from senescent leaves prior to abscission,NRE and PRE,respectively) of Leymus chinensis (Trin.) Tzvel.,a typical perennial grass species in northern China,were examined along a water supply gradient to explore how plant nutrient conservation responds to water change. Increasing water supply at low levels (< 9000 mL/year) increased NRP,PRP and PRE,but decreased green-leaf N concentration. It did not significantly affect green-leaf P concentration or NRE. By contrast,all N and P conservation indicators were not significantly influenced at high water supply levels (> 9000 mL/year). These results indicated that changes in water availability at low levels could affect leaf-level nutrient characteristics,especially for the species in semiarid ecosystems. Therefore,global changes in precipitation may pose effects on plant nutrient economy,and thus on nutrient cycling in the plant-soil systems.
为了了解草原生态系统氨气挥发情况、历史放牧的影响及其影响机制,2005和2006年生长季期间,在长达17年放牧处理的样地上测定了5个放牧强度下的氨气挥发量。结果表明:氨气挥发随季节变化波动很大,春季和初秋高,晚秋和夏季低,变化范围为0.88-3.52 gN ha^(-1)d^(-1)。土壤pH值、NH_4^+-N浓度、湿度以及容重对氨气挥发控制作用较强。但是容重的影响与其他3个因子的影响作用相反,而容重的大小直接受不同放牧强度影响。虽然不同的放牧强度对氨气释放的影响在统计学上来说并不显著,但是,相对不放牧的情况而言,氨气挥发量在放牧情况下更大。而土壤氮浓度、植物生物量却在放牧的情况下更低。这些都意味着放牧草地生态系统比不放牧草地生态系统恢复起来会更慢。这种关于草原生态系统氨气挥发的研究意义重大,因为它有助于加强了解氮素丢失对草原各进程的抑制作用,同时对制订适宜的放牧及施肥措施从而达到合理利用资源的目的也具有重要的参考价值。
