Phenophase variations and influencing factors of Salix matsudana in Xizang from 2001 to 2022
To reveal the spatial-temporal pattern of Salis matsudana phenology in response to climate change on Ti-betan Plateau,both the phenophase data and daily meteorological data at Tsedang,Xigazê,and Nyingchi from 2001 to 2022 were analyzed to identify the change trend of phenophase of S.matsudana and its influencing factors.The phenophase data included leaf bud enlargement date(LED),first leaf unfolding date(LUD),first flowering date(FFD),end of leaf coloring date(LCD),and end of leaf fall date(LFD).The daily meteorological factors included the daily average temperature(Tm),maximum temperature(Tmax),minimum temperature(Tmin),tem-perature daily range(TDR),relative humidity(RH),precipitation(Pr),sunshine duration(S),and accumula-ted temperature above 0 ℃(∑ T0).These data were analyzed with linear regression,Pearson correlation coeffi-cient,and stepwise regression methods.The results showed that:(1)Spatially,the earliest spring phenophase(LED,LUD,and FFD)of S.matsudana occurred in Nyingchi while the latest occurred in Xigazê.However,this phenomenon was exactly opposite for the autumn phenophase(LCD and LFD).The length of growth season(LOS)ranged from 238 to 268 days,with the largest value in Nyingchi and the smallest in Xigazê.(2)On the temporal scale,all phenophases of S.matsudana delayed in Xigazê and Tsedang,but only the autumn phenophases of S.matsudana delayed in Nyingchi in the past 22 years.The LOS of S.matsudana was prolonged in Xigaze and Nying-chi at growth rates of 11.90 and 6.12 d·10 a-1,respectively.In contrast,the LOS of S.matsudana was shortened at a rate of 4.50 d·10 a-1 in Tsedang.(3)Increasing trends of Tm during the growing season of S.matsudana were found in Xizang,but the increasing trends were different for Tmax and Tmin.The increased TDR and S and decreased Pr occurred in Tsedang and Xigazê,but this situation was opposite in Nyingchi.∑ T0 increased significantly in Xigazê and Nyingchi,but decreased significantly in Tsedang.(4)Air temperature was the leading meteorological factor influencing spring phenophases.In contrast,precipitation only exerted the greatest influence on the LCD of S.matsudana at Tsedang and Nyingchi,and the LFD at Tsedang.The monsoon index(MI)was only significantly cor-related with the LED and FFD of S.matsudana at Tsedang station,but did not correlate with the phenophases at other two stations.Significant correlations between MI and Tm,Pr and S occurred ubiquitously at all stations over the Tibetan Plateau in July,while MI showed a significant negative correlation with S in August.Although these meteorological factors were not the main factors affecting phenophases,they would also play an indirect role.
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