人类活动和全球变化引起了全球和区域降雨格局的改变.大量的研究表明,降雨影响全球不同草地生态系统的群落组成,但目前很少有研究从物种水平揭示高寒草原植物群落如何响应降雨变化的生态学过程.本研究利用在青藏高原建立的长期(6年)控雨试验平台,包括减少降雨50％、增加降雨50％和对照3个处理,从优势种地上和地下性状揭示高寒草原植物群落响应降雨变化的生态学过程.研究结果表明,长期减少降雨改变了植物群落的结构,主要体现在优势种丛生禾草紫花针茅(Stipa purpurea)逐渐被根茎禾草赖草(Leymus secalinus)所取代.进一步通过比较紫花针茅和赖草的地上和地下性状,发现减少降雨主要促进了赖草根系向深土层的生长、增加了地下碳的分配和减少了叶片宽度,而紫花针茅的这些性状并没有发生显著的改变;另外,减少降雨增加了赖草根茎生物量、总长度、直径及其节上根的数目.赖草这些性状的改变可能增加了对深土层水分的利用能力,以及减少了水分的蒸腾,从而增强了其在干旱胁迫过程中的竞争力.因此,我们的研究结果强调了优势种的地上和地下性状在高寒草原植物群落组成对降雨变化响应过程中起着极其重要的作用.“,”Aims Human activities and global changes have led to alterations in global and regional precipitation regimes.Despite extensive studies on the effects of changes in precipitation regimes on plant community composition across different types of grassland worldwide,few studies have specifically focused on the effects of precipitation changes on high-altitude alpine steppe at community and plant species levels in the Tibetan Plateau.Methods We investigated the effects of growing-season precipitation changes(reduced precipitation by 50％,ambient precipitation,enhanced precipitation by 50％)for 6 years on plant community composition in an alpine steppe of the Tibetan Plateau by linking above-to belowground traits of dominant species.Important Findings We found that reduced precipitation shifted community composition from dominance by bunchgrass(primarily Stipa purpurea)to dominance by rhizomatous grass(primarily Leymus secalinus).Roots and leaf traits of L.secalinus and S.purpurea differed in their responses to reduced precipitation.Reduced precipitation enhanced root vertical length and carbon(C)allocation to deep soil layers,and decreased the leaf width in L.secalinus,but it did not change the traits in S.purpurea.Moreover,reduced precipitation significantly enhanced rhizome biomass,length,diameter and adventitious root at the rhizome nodes in L.secalinus.These changes in traits may render rhizomatous grass greater competitive during drought stress.Therefore,our findings highlight important roles of above-and belowground traits of dominant species in plant community composition of alpine steppe under precipitation change.