Abstract: This paper concerns with the studies of the diurnal changes of photosythesis and transpiration of Puccinellia tenuiflora which was planted on Songnen alkalized grassland for one to three years. Diurnal changes of photosynthesis and transpiration of P. tenuiflora growing for one year is different from that growing two and three years. Diurnal changes range of photosynthesis rate and transpiration rate of P.tenuiflora growing one year is larger than that of growing two and three years. and it's water use efficiency is lower than that of growing two and three years.

Key words: Pucrinellia tenuiflora, Growing years, Photosynthetic and transpiration character, Diumal changes