青藏高原东缘季节性放牧高寒草甸植物功能性状多样性与群落结构特征的联系

Linking plant functional trait diversity and community structure characteristics in a seasonal grazing alpine meadow on the eastern Qinghai-Tibet Plateau

季节性放牧是青藏高原东部高寒草甸的普遍放牧方式,为适应长期不同季节的放牧干扰,植物群落结构、物种组成及功能性状可能也随之调整,且群落结构与多样性性状之间可能存在重要的联系.因此选取青藏高原东部高寒草甸(连续10年以上季节性放牧历史)的冷季(11月至翌年5月)、暖季牧场(6-10月)分别进行植物群落特征调查,并测定其优势物种的功能性状(株高、生物量和叶性状等),研究植物功能性状多样性与群落结构特征之间的联系.结果表明冷季牧场的植物群落高度(25.03 cm)显著高于暖季牧场(21.28 cm;P<0.05),物种均匀度指数(0.90)显著低于暖季牧场(0.91;P<0.05);群落盖度、物种多样性指数无显著差异;冷、暖季牧场样方中植物物种分别为43种和37种,分属15科和13科,皆以双子叶杂草重要值为最大,禾草类物种重要值无显著差异,但暖季牧场的莎草类和豆科植物的重要值均高于冷季牧场.暖季牧场植物的比叶面积、叶片干物质含量及叶生物量分配均高于冷季牧场(P<0.05);暖季牧场的植物个体高度、生物量、叶片性状种间差异值以及功能丰富度值均呈现高于冷季牧场趋势(P<0.05).因此,相较于冷季放牧,长期暖季放牧植物群落特征趋于矮小化与集中化,功能多样性更为丰富,种间竞争更为激烈,同时长期暖季放牧提高了植物对空间资源和光资源的利用效率;本文阐释了不同放牧情景下植物的功能性状及其在群落和个体尺度上的功能链接,可为青藏高原东部高寒草甸设置合理季节性放牧促进草地生态系统可持续发展提供理论基础.

Seasonal grazing is a common grazing practice in the alpine meadows of the eastern Qinghai-Tibet Plateau.The composition and structure of plant communities may vary when grazing in different seasons;thus,functional traits may also be adjusted to accommodate long-term seasonal grazing disturbances,although it is not yet known whether there is a link between the two.In this study,we selected the cold season(November to April of the following year)and warm season pastures(June to October)in alpine meadows on the eastern Qinghai-Tibet Plateau with a long-term seasonal grazing history of over 10 years to investigate plant community characteristics and functional traits(plant height,biomass,and leaf traits)of their dominant species and study the association between plant functional trait diversity and community structural characteristics.The results showed that the evenness of plant community characteristics was significantly higher(P<0.05)and community height was lower(P<0.05)during warm season grazing than during cold season grazing.The species composition of the plant communities differed between the different grazing seasons.Alpine communities inhabited 43 and 37 species belonging to 15 and 13 families,respectively,in the cold and warm grazing seasons.Forbs had the largest importance values of plant communities in both cold and warm seasons,but no significant difference in the importance values of grasses between the two seasons.However,the importance values of sedges and legumes were higher in the warm grazing season than those in the cold season.The specific leaf area,leaf dry matter content,and leaf distribution of the long-term warm season grazing plants were significantly higher(P<0.05)at the community level than those in the cold season.The values of interspecific variation among traits revealed a tendency for interspecific variation in plant leaf traits to be higher under warm season grazing than under cool season grazing,with significant differences in individual plant height,biomass,specific leaf area,and leaf dry matter content(P<0.05).At the same time,the functional richness values in warm season grazing were significantly higher than those in cool season grazing(P<0.05).This indicated that plants invested more in leaves under long-term warm season grazing and leaf and individual plant height traits were more abundant and varied.Leaf and induvial plant height traits improved the efficiency of plant use of light and spatial resources.The plant community structure tended to be concentrated under warm season grazing,while it was dispersed under cold season grazing.This may be due to competition for lateral investment in plants during warm season grazing.Plant functional traits were more sensitive to seasonal grazing than to community diversity,and plant community characteristics tended to be dwarfed and concentrated under warm season grazing,with more functional diversity and more intense interspecific competition.Thus,warm season grazing improved the efficiency of plants using spatial and light resources compared to cold season grazing.This study explains the life history responses of plants under different grazing scenarios and the links between functional traits and community characteristics that can provide a theoretical basis for the sustainable development of grazing ecology in alpine meadows on the Qinghai-Tibet Plateau with rational seasonal grazing pastures and cyclical alternations of cold and warm season pastures.