Study On Water Source And Utilization Of Populus Simonii With Different Degradation Degree In Bashang Area

Water is a key limiting factor for plant growth in arid regions.Populus simonii is a typical shelterbelt tree species in Zhangbei area,and plays an important role in ecological barrier.In order to reveal the cause and mechanism of the large-scale decline of Populus simonii in this area in recent years,analyzed the water sources and water use strategies of populus simonii with different degrees of degradation in different periods in Zhangbei region by using stable isotope technique,graphical method and multiple linear mixing model.The main research results of this paper are as follows:(1)The root system of Populus euphratica is "umbrella" distribution,which can stretch 240 cm and 200 cm in the vertical and horizontal directions respectively;The root morphology of Populus euphratica is a "two-state" structure,it can absorb different levels of soil water flexibly;The more serious the degradation degree is,the lower the soil moisture content is,and the ?D and ?18O values of soil water gradually increase,and the isotopic fractionation effect is significant;With the increase of the degree of degradation,the water source of Populus simonii gradually transferred from deep soil water to surface soil water.(2)In the whole growing season,the water sources of Populus microphylla with different degrees of degradation are obviously different.In May,the water source of non degenerated Populus microphylla was single,and the main water source was soil water in0-40 cm layer;In June,the sources of water absorption increased,and the utilization of80-200 cm soil water increased,the main water sources were 0-40 cm,40-80 cm and80-120 cm layers of soil water;In July(the peak season of growth),the water demand increases,the water absorption sources also increase,and the water absorption layer moves down,the main water source is the soil water of 120-200 cm,200-280 cm and280-400 cm layers;In August,the main water source was soil water of 120-200 cm and200-280 cm layers;Since September,the growth period began,the growth demand of plants also decreased,and the water source was more simple than the growing season,the main water source was 120-200 cm and 200-280 cm layer of soil water;In October,the main water source is soil water of 200-280 cm layer.The slightly degraded Populussimonii in May had a main water source of 0-40 cm layer of soil water;In June,the main water source was 0-40 cm layer of soil water;In July,the main source of water was more,120-200 cm,200 soil water in 280 cm and 280-400 cm layers;August 80-120 cm,120-200 cm and 200-280 cm layers of soil water;Populus simonii gradually entered the end of growth period in September,the main water source was 80 ~ 120 cm layer of soil water,while groundwater is also the main source of absorption;In October the main source of water is 200 ~ 280 cm and 280 ~ 400 cm layer of soil water.The water source of moderately degraded Populus microphylla is simpler than that of non degraded and slightly degraded Populus microphylla,and the utilization rate of deep soil water is reduced.From May to September,the main water source is 0-40 cm layer of soil water,and from October,the main water source is 40-80 cm layer of soil water.During the whole growing season,the water source of the seriously degraded Populus microphylla was stable(0 ~ 40 cm),basically unchanged.(3)With the aggravation of the degradation degree,the Bai of Populus euphratica decreased gradually,the ? 13 C value increased gradually,the more obvious the isotopic fractionation was,the greater the i WUE was;the correlation between i WUE and environmental factors such as precipitation,temperature,relative humidity was significant,and there was a significant positive correlation between i WUE and temperature,and the correlation between i WUE and relative humidity was the least significant.(4)The difference of water use pattern of trees is due to the difference of water source and water use efficiency of trees.The water source of Populus euphratica has changed significantly in different degrees of degradation.During the whole growing season,the water source of Populus euphratica has not been degraded or slightly degraded,and it transfers from shallow soil water to deep soil water and then to shallow soil water,and the water use efficiency is low;During the whole growing season,the water source of medium degenerated Populus microphylla is simple,and the water use efficiency of deep soil is reduced,which is higher than that of non degenerated Populus microphylla;The water source of seriously degraded Populus microphylla is stable,and the soil water with the shallowest water absorption depth(0-40 cm)layer has the highest water use efficiency.