Study On Water Use Efficiency And Response To Climate Of Typical Vegetation In Loess Plateau

Since the implementation of Grain for Green Project in the Loess Plateau,the ecological environment has been greatly restored,and the vegetation coverage has increased significantly,among which the tree forest is more obvious in economic forest apple and ecological forest black locust.However,large-scale planting of apples and black locust also brought new ecological problems,such as soil drying,vegetation degradation and so on.In the context of global warming,with the rise of air temperature and the increase of water consumption,coupled with the small and deep groundwater reserves in the Loess Plateau,insufficient precipitation recharge,water gradually restricts the growth of plants.In order to further evaluate and predict the sustainability of vegetation restoration,regional water use efficiency and its response to the environment must be studied.This paper takes the leaves and rings of apple and black locust from 22 sampling sites in the Loess Plateau as the research object,based on stable carbon isotope technology,through field sampling and investigation,laboratory experiments,data statistical analysis and other methods,to analyze the effects of different artificial management measures（fertilization management,pruning management,weed management,sowing measures and soil mulching measures）on the WUE of apple and black locust.The response and main control factors of the WUE of apple and black locust to different climates（rainfall,temperature,sunshine time,relative humidity,water vapor pressure and SPEI,etc.）and the differences in different climatic regions were analyzed by correlation analysis.The following conclusions are drawn:（1）Based on the analysis of the difference of WUE between apple and black locust by stable carbon isotope technology,it is found that the foliar WUE of apple is greater than that of black locust,and the results of WUE of apple and black locust rings are consistent with that of leaves;The frequency distribution of foliar WUE in apple and black locust is as follows:95%of the foliar WUE in black locust is between 3.0-4.66 mmol CO₂/mol H₂O,and 95%of the foliar WUE in apple is between 3.22-5.36 mmol CO₂/mol H₂O.The distribution of foliar WUE value of black locust is lower than that of apple;Reasonable fertilization management,pruning management,weed management,sowing measures and soil cover measures can improve plant WUE in varying degrees by affecting soil nutrients,photosynthetic rate and transpiration rate;Because Apple is subject to many human management factors,most of them maintain a high WUE,while black locust is lack of human management.WUE changes greatly under the influence of the environment and is prone to the phenomenon of maximum and minimum.Therefore,the Loess Plateau should strengthen the fine management of black locust forest and other arbor forests,appropriately increase man-made management measures to improve the WUE,maintain reasonable planting density and structure,adapt land and trees,and further promote the sustainable development of Grain for Green Project.（2）On the whole,the Loess Plateau has less rainfall and high temperature in the northwest,which is relatively arid,and more rainfall and low temperature in the southeast.Therefore,the WUE of apple and black locust also show the characteristics of high in the northwest and low in the southeast;In the analysis of foliar WUE response to climate factors,it was found that foliar WUE had a significant positive correlation with sunshine time,a significant negative correlation with rainfall,temperature,relative humidity,water vapor pressure and SPEI,a significant positive correlation between foliar WUE of Apple and altitude,and no significant correlation between foliar WUE of black locust and altitude;The foliar WUE of apple and black locust in the semi-arid area were higher than that in the semi-humid area.The foliar WUE of apple in the semi-arid area was 12.5%higher than that in the semi-humid area,and the foliar WUE of black locust in the semi-arid area was 6.4%higher than that in the semi-humid area;The main climatic factors affecting foliar WUE of apple and black locust are sunshine time,relative humidity and rainfall.The explanatory degrees of foliar WUE changes are 26.9%,16.7%and 6.8%respectively;Therefore,the Loess Plateau should pay attention to the change difference of WUE,adapt to the land and trees,and fully consider the local climate factors.（2）In the analysis of the response of ring WUE of apple and black locust to climate factors,the precipitation and air humidity increased in Yan’an and Changwu,the WUE of apple ring decreased significantly with time,and the WUE of black locust ring did not change significantly with time;The climate regions difference of the WUE of apple and black locust ring is similar to that of foliar WUE.The WUE of plants in semi-arid area is higher than that in semi-humid area.The WUE of apple ring in semi-arid area is 3.13%higher than that in semi-humid area,and the WUE of black locust ring in semi-arid area is 1.2%higher than that in semi-humid area;In the correlation with monthly climate,the response of WUE of tree ring in Yan’an in semi-arid area is more obvious than that in Changwu in semi-humid area,and the correlation between the WUE of black locust ring and monthly climate is more obvious than that of the WUE of apple ring in the same area;In the correlation with annual scale climate,it is basically consistent with the correlation of foliar WUE to climate;However,there are differences in the main climate factors affecting the of ring in different regions.The main factors affecting the WUE of apple and black locust ring are the sunshine time and rainfall respectively in Yan’an,and the relative humidity has a more significant impact on the WUE of apple and black locust ring in Changwu.This study expands the study of plant WUE on the Loess Plateau,which can provide reference for understanding plant WUE and its response to climate change in the Loess Plateau of China,and provide decision-making suggestions for improving WUE,fine,scientific and sustainable development of Arbor forest management in this region,and further promote the sustainable development of Grain for Green Project in the Loess Plateau.