Abstract: Photosynthetically active radiation (PAR) is an important parameter in the process of ecosystem. However,there are few reports on the change of PAR in alpine wetland. In this paper,the characteristics of PAR variation in the alpine wetland were analyzed based on the radiation data from the Xiaobohu and Wayanshan wetland meteorological stations in the Qinghai Lake Basin.The results showed that the annual global radiation (Q) and PAR at Xiaobohu Meteorological Station were 6 711.6 MJ·m^-2 and 2 888.3 MJ·m^-2,but they were 5 963.4 MJ·m^-2 and 2 527.5 MJ·m^-2 at Wayanshan Meteorological Station,respectively.The values of Q and PAR at the Wayanshan station were significantly lower than those at the Xiaobohu station.The daily and seasonal variations of both Q and PAR values at the two sites were obvious,and the maximum values of Q and PAR occurred around 13:00 o’clock.The maximum Q and PAR values appeared in June,and the minimum ones in December.The average annual photosynthetically active radiation coefficients (η_PAR) at the Xiaobohu and Wayanshan stations were 0.43 and 0.44 respectively.The seasonal variation of η_PAR at both sites was also obvious,the maximum value appeared in July,and the main reason was that the water vapor content over the Qinghai Lake Basin was the highest in July.Finally,a statistical model was developed based on the clearness index (K_t) and total solar radiation (Q) data at the Wayanshan station so as to estimate the PAR values in the whole Qinghai Lake Basin.The model was also verified at the Xiaobohu station,the results showed that the model could be used to meet the requirements of estimating the PAR values under different weather conditions in the Qinghai Lake Basin.

Key words: global radiation, photosynthetically active radiation, alpine wetland, Qinghai Lake Basin