Differences In Water Sources Of Woody Plants In The Forests Of Tianshan Mountains In Summer

Exploring the source of plant water is not only conducive to the in-depth understanding of plant growth and survival status,but also enables scholars to deeply understand the plasticity response of different plants in the ecosystem to the variation of environmental water conditions,which helps to predict the changes of vegetation dynamics and species composition in the ecosystem under the background of global climate change.Studies on climate change in the future predict that the precipitation pattern will change.The change of precipitation pattern may change the water source and water use pattern of coexisting plants in mountain coniferous forest in arid and semi-arid areas,and then have a profound impact on the forest community structure,vegetation composition and ecosystem function.It is of great theoretical and practical significance to understand the water sources and water use patterns of coexisting tree species in different types of mountain coniferous forest communities in arid and semi-arid areas.The forests of Tianshan Mountains is the main part of arid mountainous area,and plays an extremely important role in the water cycle、water conservation and soil and water conservation in the arid areas.At the same time,The community structure Tianshan Mountains is relatively simple and there are a few woody plant species.However,the water competition patterns among the woody plants in the Tianshan Mountains is not clear due to lack of quantitative analysis related to water use dynamics of the woody plants.In this study,two sample plots were set up in the Picea schrenkiana coniferous forest community and the piedmont shrub community in the Tianshan Mountains,The hydrogen and oxygen stable isotope composition of xylem water of different tree species and their potential water sources in the two communities in study area was measured in this study by using stable isotope technology.In order to explore the differences and dynamic in water sources of different tree species in the two communities of Tianshan Mountains,the Iso Source model was used to analyze quantitatively the relative contributions of each potential water source used by the different tree species.The results showed that:(1)In the Picea schrenkiana coniferous forest community,in July,when the soil water content was sufficient,the Picea schrenkiana and the Berberis heteropoda mainly extracted soil water above 60 cm,and the relative utilization ratios were 73.80 %and 63.20 % respectively.In August,when the soil water content decreased,the water source of Picea schrenkiana remained stable,that is,it still mainly relied on soil water above 60 cm,and the relative utilization ratio was 69.5 %.The Berberis heteropoda converted to deep soil water,and its relative utilization ratio of 0-20 cm shallow soil water drops to 14.30 %,it mainly extracted middle and deep soil water(20-60 cm and60-100 cm),the relative utilization ratio was 67.7 %.In September,when the shallow soil water content increased,the two tree species resumed the extraction of shallow soil water,and their relative utilization ratio reached 95.00 %.Their water utilization sources reflect the typical shallow root characteristics of Picea schrenkiana,while Berberis heteropoda can extract water in the soil layers of 0-100 cm,and at the same time,it can flexibly convert its water source with changes in soil water content.So as to deal with the environmental water variation.(2)In the piedmont scrub community,in July,when the 0-20 cm shallow soil water content was sufficient,Rosa spinosissima、Cotoneaster melanocarpus and Spiraea hypericifolia extensively extracted shallow soil water,and the relative utilization ratio was higher than 89.3 %.On contrary,Berberis heteropoda absorbed water from all the potential water sources(30.70 % of shallow soil water,29.4 % of middle soil water,25.7 % of deep soil water,14.2 % of stream water,the same below);In August,when the water content of the shallow soil decreased,the Rosa spinosissima converted to 60-100 cm deep soil water and stream water,and the relative utilization ratios were 64.8 % and 27.0 %,respectively.Cotoneaster melanocarpus and Spiraea hypericifolia extracted water from all the potential water sources in similar proportions(33.8 % and 36.8 %、30.9 % and 29.7 %、23.5 % and22.3 %、11.8 % and 11.2 %).Berberis heteropoda relied mainly on the stable deep soil water below 80-100 cm;In September,when the shallow soil water content increased,the all of the four shrubs absorbed large amount of shallow soil water,and the relative utilization ratio was higher than 72.20 %.This indicates that the main tree species of the shrub community in Tianshan Mountains could convert the plasticity of the water sources to deal with the environmental water variation,by dividing the water sources in time and space to reduce the pressure of competition on water resources,which would promote the coexistence of species through niche differentiation in water resource utilization.(3)The water sources and water use strategies of Berberis heteropoda in the two communities were mainly due to the differences of water competition and soil water content in different communities.In addition,the soil water supplied by the melting water of glaciers in the study area is also one of the important plant water sources in the forest ecosystem.