Radial Growth Of Populus Euphratica Under Different Groundwater Levels And Its Response To Climate Factors

In this paper,the study area is the An-Soviet section of the lower reaches of the Tarim River,and two monitoring samples with different distances from the river are selected based on the typical plant Populus euphratica as the research object.From April to October 2020,Populus euphratica was sampled with a micro-growth cone every week,and after sample processing and other steps,the intranmusional radial growth width and xylem catheter anatomical characteristics of poplar were obtained,and the GAMs model was used to fit the intra-year radial growth dynamics and growth rate of Populus euphratica,and the basic characteristics and physiological mechanisms of Populus euphratica formation layer activity were clarified.The intra-year radial growth of Populus euphratica and the characteristics of Populus euphratica xylem ducts at different river distances and their response to climatic factors were discussed,the radial growth rate and sensitive water level of Populus euphratica under different groundwater burial depths were studied,the internal mechanism of Populus euphratica growth was revealed,and the theoretical basis was provided for the protection and management of Populus euphratica in arid desert areas,and the basis for the ecological and environmental protection of Tarim River.The main conclusions of this study are as follows:（1）Populus euphratica xylem cell enlargement begins on April 14（DOY106）and ends on September 27（DOY270）.The duration of the xylem growth season was 164 days,the cumulative growth of xylem was about 3000 μm,and the average growth rate of Populus euphratica was 19 μm/day.There are differences in the stages of Populus euphratica wood partialization between different distances from the river,the start time of F2 cell expansion and the start time of cell wall thickening closer to the river are the earliest,the end of cell expansion and the end of cell wall thickening are late,the total growth of xylem is the largest,and the average growth rate is the fastest,The F10 cell enlargement farther from the river began at the latest,the cell enlargement ended at the earliest,and the xylem formation layer activity of Populus euphratica was affected by the distance from the river.Through the study of the radial growth of Populus euphratica at different distances from the river,it is found that the radial growth width of Populus euphratica in the F2 monitoring well is greater than that of the Populus euphratica in the F10 monitoring well,indicating that the radial growth of Populus euphratica in the monitoring point closer to the river is large,and the radial growth of Populus euphratica is related to the distance from the river.（2）The GAMs was used to fit the intra-year radial growth process of Populus euphratica and found that the radial growth of Populus euphratica within the year was consistent with the basic law of tree growth,showing an“S”curve,the fit of the growth rate of Populus euphratica was a bimodal curve,and the growth rate of DOY130（April 30）and DOY190（July 9）were the best time periods for the accumulation of Populus euphratica growth.The contribution of the duration of the growing season and the growth rate to the growth of the xylem of Populus euphratica was analyzed by sensitivity,and the results showed that the growth rate contributed a lot to the radial growth of the xylem of Populus euphratica.（3）The radial growth of Populus euphratica at different distances from the river is consistent with the response to climatic factors,which is not related to the average daily temperature,the maximum daily temperature and the daily minimum temperature,is positively correlated with the relative humidity,and is significantly negatively correlated with the number of sunshine hours,indicating that the radial growth of Populus euphratica is affected by water,and the long number of sunshine hours makes the evaporation effect strong,which is not conducive to the radial growth of Populus euphratica.（4）The total duct area of Populus euphratica xylem and the number of catheters in the two monitoring points during the growing season were basically the same,and the total catheter area was directly affected by the number of catheters,and after the growing season DOY220,the number of catheters and the total catheter area of F2 closer to the river were significantly greater than those of F10,indicating that the characteristics of Populus euphratica xylem ducts were related to the distance from the river.The change trend of catheter area and catheter diameter is also basically the same,and the influence of meteorological factors on them is basically the same,mainly positively correlated with air temperature,of which the maximum catheter area and the maximum catheter diameter are negatively correlated with the number of insolation hours;the correlation between the minimum catheter area and the minimum catheter diameter and the meteorological factors is the least significant,and the influence is also the least.The catheter density is greatly affected by relative humidity,and the average catheter density in the F2 growing season is less than F10,which is different from the characteristic changes of other catheters.（5）The radial growth rate of Populus euphratica was significantly negatively correlated with the burial depth of groundwater,and the sensitive water level was 5.3 m,that is,when the groundwater burial depth was less than 5.3 m,the radial growth rate of Populus euphratica slowed down with the increase of groundwater burial depth.In this paper,it was found that the“lag” of radial growth of Populus euphratica was not significant.