Relationship Between Environmental Factors And Cambium Activity And Intra-annual Radial Of Populus Euphratica In The Lower Reaches Of Tarim River

Populus euphratica,as the main constructive species of desert riparian forest in Tarim River Basin,plays an important role in maintaining the ecological environment and preventing desertification in Tarim River Basin.Especially in the lower reaches of Tarim River,which had been cut off for a long time in history,P.euphratica is of great significance for maintaining regional ecological balance and ensuring the production of oasis agriculture and animal husbandry.In this paper,P.euphratica in Yingsu section of the lower reaches of Tarim River was taken as the research object.The cambium activity and annual inner diameter growth of P.euphratica were dynamically monitored for one year by using micro tree core method.Combined with meteorological and hydrological data,the response of air temperature to annual inner diameter growth of P.euphratica and the difference of annual inner diameter growth of P.euphratica under different water conditions were discussed,so as to reveal the seasonal dynamics of annual inner diameter growth of P.euphratica It also provides theoretical basis for scientific and reasonable ecological water transfer to restore P.euphratica forest in the lower reaches of Tarim River.The main results are as follows:(1)The growth season of P.euphratica in the lower reaches of Tarim River starts from the end of April to the beginning of May,and ends from the beginning of August to the beginning of September.The growth season lasts for 4-5 months.The maximum annual radial growth rate of P.euphratica occurs in early June,1-3 weeks earlier than the summer solstice.The accumulation of radial growth of P.euphratica was mainly in May,June and July.The accumulation of radial growth of P.euphratica was the most in June,and the radial growth rate was the fastest in June.Therefore,the best ecological water delivery time for P.euphratica forest in the lower reaches of Tarim River should be in May and June.(2)The sensitivity analysis showed that growth rate and growth season duration contributed81.29% and 18.71% to the radial growth of P.euphratica in the lower reaches of Tarim River,respectively,indicating that the contribution of growth rate to the radial growth of P.euphratica was greater than the growth season duration,so the radial growth of P.euphratica was mainly determined by growth rate.From the whole growing season,the radial growth rate of P.euphratica was negatively correlated with air temperature,but not significantly,which indicated that the drought stress caused by high temperature had a negative effect on the radial growth rate of P.euphratica,that is,the water condition may be the limiting factor affecting the radial growth rate and the radial growth of P.euphratica.(3)There were significant differences in the occurrence time of the maximum radial growth rate of P.euphratica between the two sampling points with different groundwater levels in the lower reaches of Tarim River.The occurrence time of the maximum radial growth rate of P.euphratica in the sampling point with lower groundwater level was earlier than that in the sampling point with higher groundwater level,and the difference was 10 days,which indicated that drought might lead to the occurrence time of the maximum radial growth rate of P.euphratica in advance,and then affect the growth of P.euphratica Accumulation of radial growth of P.euphratica.(4)With the decrease of groundwater level,the radial growth rate of P.euphratica in the lower reaches of Tarim River will increase first and then decrease,and the increasing rate of radial growth rate of P.euphratica is greater than the decreasing rate.When the groundwater level dropped to 5.07 m,the decline rate of radial growth rate of P.euphratica changed from increasing to slowly decreasing.When the groundwater level continued to drop to 5.46 m,the decline rate of radial growth rate of P.euphratica began to increase again,indicating that when the groundwater level dropped to 5.07 m,the radial growth of P.euphratica might be under drought stress Some physiological adjustments were made to slow down the decline of growth rate,and the radial growth of P.euphratica was accumulated to a certain extent.