Abstract: The diurnal chang es of photosynthesis and transpiration of bo th natural and planted one to three years Puccinellia tenuiflora at heading stage, climate factors such as light in-tensity, atmospheric temperature, ground temperature, CO₂? concentration and relative humidity are measured.The relationships between diurnal changes of photosynthesis and transpiration of P.tenuiflora and the climate factors are analysed by correlation coefficient and path coefficient analysis.The relative humidity of atmosphere affects the diurnal changes of the photosynthesis and transpiration characters suth as photosynthesis rate, transpiration rate and water use efficiency of P.tenuiflora at heading stage most, follow ed by the ground temperature and CO₂? concentration.The light intensity and atmospheric temperature influence the diurnal changes of photosynthesis and transpiration characters indirectly by acting on the relative humidity of atmosphere.

Key words: Puccinellia tenuiflora, photosynthesis and transpiration character, diurnal change, climate factors