放牧对高寒草地4种草光响应和荧光特性的影响

在祁连山东段天祝县南泥沟河谷地的披碱草-嵩草型草地设置禁牧(Non grazing grassland,NG)和放牧(Grazing grassland,G)两块样地，选取矮嵩草(Kobresia humilis)、垂穗披碱草(Elymus nutans)、扁蓿豆(Melissitus rutenica)、黄花棘豆(Oxytropis ochrocephala)4种优势植物，测定了4种植物的光合-光响应曲线(Pn PAR curves)和叶绿素荧光特性。结果显示，4种植物在放牧后：1)对强光的适应能力增强而对弱光的利用能力降低。垂穗披碱草、矮嵩草、扁蓿豆的最大净光合速率(Pmax)显著降低，即光合潜力降低；而黄花棘豆的Pmax却显著升高，光合能力增强。2)叶绿素初始荧光(F0)成像颜色加深，说明叶绿素含量有所降低，尤以垂穗披碱草、矮嵩草最为明显。3)PSⅡ最大量子产量(Fv/Fm)、光化学猝灭系数(qP)、电子传递速率(ETR)值显著降低，而非光化学猝灭系数(NPQ)值升高。综合各项指标来看，放牧后黄花棘豆这种毒草的光合能力提高，而其他3种优质牧草的光合能力下降。

Influence of grazing on photosynthesis-light response and fluorescence parameters of four plants in alpine grassland

Two plots,non-grazing(NG) and grazing(G) grassland,were designed to determine the influence of grazing on photosynthesis-light response and chlorophyll fluorescence characteristics of Kobresia humilis,Elymus nutans,Melissitus rutenica,Oxytropis ochrocephala growing in the alpine grassland at Nanni Valley,Tianzhu County of the eastern Qilian Mountains.The results of this study showed the grazing increased the adaptability of the four plants to glare and reduced the ability to use low light.In grazing conditions Pmax of K.capillifolia,E.nutans,and M.rutenica reduced significantly,which reduced their photosynthetic potential,but Pmax of O.ochrocephala increased significantly,which enhanced its photosynthetic capacity.Image of minimal fluorescence(F0) of the four plants deepen the color in the grazing condition,especially K.capillifolia and E.nutans.The maximal quantum yield of PSⅡ(Fv/Fm),photochemical quenching coefficient(qP) and electron transport rate(ETR) of the four plants reduced significantly and the non-photochemical quenching coefficient(NPQ) increased significantly in the grazing conditions.From all measured indicators,this study indicated that the grazing increased the photosynthetic capacity of O.ochrocephala,a kind of weeds but reduced the photosynthetic capacity of other three plants with high quality.