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中文摘要：
【目的】研究土壤干旱对华北落叶松幼苗生长与生理的影响,揭示该种的苗期耐旱性与生长策略,预测干旱气候对幼苗更新的影响,为评估未来气候变化下该种的种群动态与制定合理的经营措施提供理论支撑,同时也为干旱地区的人工林营造特别是苗木管护提供依据。【方法】以当年生华北落叶松幼苗为试验材料,在盆栽条件下,采用称重控水法,将土壤相对含水量分别控制在最大田间持水量的70%~80%（对照）、50%~60%（轻度干旱）、35%~50%（中度干旱）和20%~35%（重度干旱）,研究不同干旱处理对华北落叶松幼苗生长、叶绿素含量、抗氧化系统和渗透调节的影响,分析幼苗耐旱性,确定该种的干旱胁迫阈值。【结果】轻度干旱对华北落叶松幼苗针叶和幼茎的伸长生长影响较小,中度和重度干旱显著抑制针叶和茎的伸长生长,3种干旱处理均明显促进侧根的发生与伸长,干旱时幼苗的针叶长与主根长紧密相关;针叶的叶绿素总量和叶绿素a含量对轻度干旱无明显反应,随干旱加强而持续下降,重度干旱时叶绿素b含量下降,但3种干旱强度下的叶绿素a、叶绿素b含量之比无明显变化;随干旱加强,华北落叶松幼苗的SOD酶和POD酶活性持续增强,丙二醛和脯氨酸含量持续增加,可溶性蛋白质含量下降,茎的可溶性糖含量持续增加,针叶和根的可溶性糖含量先增后减;干旱条件下幼苗的抗氧化系统和脯氨酸含量在3种营养器官之间紧密相关。【结论】华北落叶松当年生幼苗的生长和生理作用几乎不受轻度干旱的影响或仅受较小影响,但受中度和重度干旱的影响显著。干旱条件下,华北落叶松幼苗采取减少地上部分生长、优先满足根系的生长策略,并启动抗氧化系统和积累脯氨酸来减轻干旱造成的伤害,具一定的耐旱性;针叶的生理变化先于形态变化,未出现针叶变黄脱落的现象;中度和重?
英文摘要：
【Objective】Larix principis-rupprechtii,a deciduous conifer tree species,is an important forest component and timber resource in subalpine of North China. This species is mainly distributed in subalpine regions of Shanxi province where droughts have occurred frequently in recent decades. In this study,drought effects on seedling growth and physiological responses of L. principis-rupprechtii were carried out to analyze its drought resistance and growth strategy at early stage. This study intends to provide a basis for afforestation,especially for seedling management and protection of this species. It can also efficiently predict regeneration of the species under the drying climate. 【Method 】A potted experiment with one-year-old seedlings of L. principis-rupprechtii was carried out with four water regimes by controlling soil water content using weighing method. Light drought（ LD） was treated as 50%- 60%,moderate drought（ MD） as35%- 50%,severe drought（ SD） as 20%- 35%,and control（ CK） as 70%- 80% of field water carrying capacity,respectively. For each treatment,length of needles,stems and primary roots of the seedlings were measured,and lateral roots of each seedling were counted and measured to analyze drought effects on elongation growth of vegetative organs.Physiological indexes, including needle chlorophyll contents, antioxidants, i. e. SOD, POD activities and malondialdehyde（ MDA） contents,and osmotic substances,i. e. proline,soluble sugar and protein were also measured toanalyze seedling physiological changes. Then drought resistance of the one-year-old seedling was analyzed and drought stress threshold was estimated on the basis of above indexes. 【Result】Elongations of needles and stems of L. principisrupprechtii seedlings were significantly restrained by both the moderate and severe drought stress,but not significantly by light drought. The formation and elongation of lateral roots were promoted by all drought stresses. There was close correlation between primary root length an
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