Effects of Exogenous Nitric Oxide on Photochemical Activity of Photosystem Ⅱ in Potato Leaf Tissue Under Non-stress Condition STUDY ON THE PHOTOSYNTHETIC CHARACTERISTICS OF THE Pennisetum alopecuroides L.SPRENG 青海高原植物生理生态学研究:Ⅱ.高寒草甸植物的光合作用 Study of Diurnal Changes in Photosynthetic Rate and Quantum Efficiency of Grapevine Leaves and Their Utilization in Canopy Management Seasonal Variation and Correlation with Environmental Factors of Photosynthesis and Water Use Efficiency of Juglans regia and Ziziphus jujuba Characteristics of photosynthetic and transpiration of three common afforestation species in the Loess Plateau