中文摘要：

【目的】氮素和水分是干旱半干旱区生态系统的主要限制因子,研究两者交互作用对干旱半干旱区植物碳（C）、氮（N）、磷（P）化学计量特征的影响有助于深入了解干旱半干旱生态系统对全球变化的响应。【方法】以黄土丘陵区退耕地典型草本植物白羊草（Bothriochloa ischaemum）为研究对象,采用盆栽控制试验,设置添加氮0（对照）、2.5 g/（m2·a）（低氮）、5.0 g/（m2·a）（高氮）三个水平;供水处理设75%-80%FC（充分供水）、55%-60%FC（轻度干旱胁迫）和35%-40%FC（重度干旱胁迫）三个水平。测定了白羊草地上部分和根系碳氮磷含量,讨论了氮素和水分供应对其化学计量特征的影响。【结果】氮素添加和干旱胁迫对白羊草地上部分和根系碳含量无显著影响,氮素添加使白羊草地上部分氮含量提高9.7%-48.8%（P〈0.001）,而干旱胁迫使其降低2.8%-28.3%（P〈0.001）。氮素添加和干旱胁迫对白羊草根系氮含量的影响表现为正常水分条件下氮素添加使根系氮含量提高25.0%-26.1%（P〈0.01）,而干旱条件下氮素添加无显著作用。氮素添加和干旱胁迫使白羊草地上部分磷含量分别降低17.4%-31.8%和12.0%-22.1%（P〈0.001）。氮素添加和干旱胁迫对白羊草地上部分C∶N的影响表现为在干旱胁迫条件下氮素添加使地上部分C∶N降低24.9%-32.9%（P〈0.05）,在正常供水条件下氮素添加无显著影响。氮素添加对根系部分C∶N有显著影响,在正常供水条件下氮素添加使根系部分C∶N降低19.8%-24.5%（P〈0.05）。氮素添加和干旱胁迫使白羊草地上部分C∶P分别提高24.4%-42.3%和12.2%-31.0%（P〈0.001）,对根系C∶P无显著影响。氮素添加显著提高白羊草地上部分N∶P,干旱胁迫对白羊草地上部分N∶P无显著影响。氮素添加和干旱胁迫对白羊草根系部分N∶P表现为在正常供水条件下氮素添加使根系部分N∶P提高26.8%-54

英文摘要：

[ Objectives ] Both nitrogen and water shortage are the main limiting factors for plant growth in arid and semiarid ecosystems. Study the carbon （C）, nitrogen （N） and phosphorus （P） stoichiometric characteristics of plant under nitrogen deposition and drought stress will help understanding the response characteristics of arid and semiarid ecosystems to global changes. [ Methods ] A pot experiment was conducted inside a phytotron using Bothriochloa ischaemum as tested martials. N application rates of 0, 2.5 and 5.0 g/（m2.a） were designed,representing CK, low N and high N rate; and water supply levels of field capacity of 75%-80%, 55%-60% and 35%-40% were setup, representing drought stress level of well-watered, moderate drought stress and severe drought stress in turn. The contents of C, N and P in the shoot and root were determined and the C, N, and P stoichiometry were calculated. [ Results ] N addition and drought stress had no significant influence on C concentration in the aboveground and root of B. ischaemum. N addition increased the N concentration by 9.7%-48.8% （P 〈 0.001） in the shoot, while drought stress decreased it by 2.8%-28.3% （P 〈 0.001）. Nitrogen addition and drought stress had significant interactive effects on the root N concentration, N addition increased the N concentration by 25.0%-26.1% （P 〈 0.01） under well-watered condition and had no significant influence on it under drought stress condition. N addition and drought stress significantly decreased the P concentration by 17.4%-31.8% and 12.0%-22.1% in shoot. N addition and drought stress had significant interactive effects on the C ： N ratio in shoot, N addition increased the C ： N ratio by 24.9%-32.9% （P 〈 0.05） under drought stress, but not under well-watered condition. The C ： N ratio in the root ofB. ischaemum was decreased by 19.8%-24.5% （P 〈 0.05） by N addition under well watered condition. N addition and drought stress decreased the C ： P ratio by 24.4%-42.3% and 12.2%-31.0% in the