| In order to understand the phenological changes of spring wheat in Tibet and its relationship with climate change,using the spring wheat growth period and meteorological data observed at the Tibetan Shigatse Agricultural Meteorological Observatory Station from 1991 to 2020,the characteristics of the changes in the growth period of spring wheat in Tibet were analyzed using linear regression,correlation coefficient and Mann-Kendall methods,and the dominant factors influencing the changes were discussed. The results showed that during the period 1991-2020,The precipitation(Pr),relative humidity(RH) and sunshine duration(S) of spring wheat growing season in Tibet showed a decreasing trend;the warming rate of mean minimum temperature(Tmin) was significantly greater than that of the mean maximum temperature(Tmax); and the mean temperature(Tm),above 0 ℃ cumulative temperature(∑T0) and mean wind speed(Ws) showed an increasing trend. The heat resources (Tm,Tmax,Tmin,∑T0) and Ws during the vegetative growth period(VGP),reproductive growth period(RGP) and whole growth period(WGP) showed an increasing trend,while S and RH tended to decrease; Pr increased in VGP,decreased in RGP,and slightly increased in WGP. The results showed that all growth stages of spring wheat presented a delayed trend,with an average of 2.33-13.36 days per decade,especially at milk ripening stage.The days of seedling-emergence and jointing-booting had no obvious response to climate change;The days of flowering-milk ripening period was significantly increased with a rate of 11.03 days per decade,while days of all other growth period showed a shortened trend,and days of VGP,RGP,and WGP appeared the shortened trends. Except for flowering,sudden climate changes occurred at all growth stages,which mainly occurred in the middle and late period of the first 10 years of the 21st century.Sudden climate changes appeared in the beginning of the 21st century only at four growth stages:three leaf-tillering,tillering-jointing,flowering-milk ripening,and milk ripening-maturity.The dominant factor affecting days of VGP and WGP of spring wheat was Tm,and the secondary factor was ∑T0,while ∑T0was the dominant factor affecting days of RGP,and Tm was the secondary factor. In the past 30 years,the days of VGP,RGP and WGP of spring wheat in Tibet has been shortened,mainly cue to the significant increasing in Tm. |
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