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.