中文摘要：

植物的碳氮营养及其相互关系是最重要的基本生物过程之一，阶段性干旱对植物碳氮分配的影响研究甚少。实验以中国北方草原的典型植物羊草为材料，研究不同干旱持续期复水对羊草碳氮含量、分配及其相互关系的影响。结果表明：短期和中期干旱使植株生物量、氮素水平和单株总氮量增加，但长期干旱使之降低。水分处理对碳含量的影响不显著。干旱后复水降低了各器官特别是绿叶的碳氮比。中度持续干旱的氮素利用率（NUE）最高、短期干旱最低。羊草各器官氮素绝对量占整株的百分比从大到小依次为：绿叶、根茎、根、枯叶和茎鞘，其中叶片的氮素总量占植株的一半以上；随着干旱持续期的增加，氮素对根部的投资亦加大。羊草受到适当干旱驯化后复水引发的超补偿作用可促进羊草植株生长、提高氮素水平，并在一定程度上通过碳氮分配的调节作用来适应于阶段性的干旱胁迫。

英文摘要：

The carbon and nitrogen nutrition and their coupling relationship are one of the most key and basic biological processes, but the effects of episodical drought on them are stiLL not well understood. The effects of rewatering on the carbon and nitrogen contents as well as their allocation, C/N ratio, nitrogen use efficiency （NUE） of Leymus chinensis in pots were investigated in different soil drought stress. The grass plants were subjected to short-term （ 10-d）, moderate-term （20-day） and long-term （30-d） drought, and then followed by rewatering. And the control plants were well watered during the experimental periods. The plant biomass, nitrogen levels and the nitrogen amount of the whole plant increased by rewatering after the short-term or middle-term drought stress, while they decreased after the long-term drought stress. There was not a significant difference among different treatments. Rewatering after drought decreased C/N ratio in different organs, especially in leaves. The rewatering after long-term drought produced the greatest NUE, but that after short-term drought was the lowest one. The green leaf nitrogen percentage in total whole plant nitrogen amount was the greatest, followed by rhizome, root, Leaf Litter, stem and sheath. And the leaf nitrogen amount was above 50 % of plant total nitrogen amount. The allocation of nitrogen into roots increased with the increase of drought duration. The present results suggested Leymus chinensis subjected to rewatering after moderate drought acclimation may produce overcompensation in plant growth and nitrogen nutrition, and this grass species may be well adapted to episodical soil drought through the regulation by carbon and nitrogen allocations to some extent.