Effects of climate change on Poa crymophila phenology in alpine meadow grassland in northern region of Qinghai Lake,Northwest China

Based on the field observation and meteorological data in the northern region of Qinghai Lake,this paper analyzed the annual fluctuation of air temperature,precipitation,and aridity index as well as the effects of this fluctuation on the phenology and aboveground production of Poa crymophila,a dominant grass species in this region's alpine meadow grassland.In the region,the mean annual air temperature increased significantly at a rate of 0.512 ℃·10 a-1,with much higher increment in autumn and winter than in spring and summer.The annual precipitation increased,mainly in spring and autumn and with an about 9-year cycle.The aridity index in the growth season of P.crymophila had an increasing trend,and from the late 1990s to 2010,it was obviously getting warmer and drier.The stages of turning green,heading,flowering,and seed maturing of P.crymophila were in advance,yellowing stage delayed,and thus,the whole growth period of this grass prolonged.The simulated results with Logistic model indicated that the growth speed of the grass was the maximum on the 72nd after turning green,being 0.29 cm plant height per day.The growth speed turned from slow to rapid from the 49th day after turning green,and turned from rapid to slow from the 95th day after turning green,with a rapid growth period of 46 days.The plant height and aboveground biomass of P.crymophila increased year by year.The production of P.crymophila was most sensitive to the heat in May.With a 1 ℃ average ten-day temperature increase,the production would be increased by 20-30 kg·hm-2.Water availability was crucial for P.crymophila during its heading and flowering stages.The production of the grass would be increased with the increase of precipitation.