| For controlling severe karst rocky desertification in Dongshan mountainous areas in Mengzi basin,a very typical karst garben basin,local government chosen apple planting as one of main industries for ecological restoration since the implementation of the national comprehensive control project of rocky desertification.Up to now,apple planting industry has achevied well economic and ecological results.Although the light and heat conditions are sufficient in this study site,the precipitation shows high temporal heterogeneity.Thus,under the controls of special karst geological background,water is the main limiting factor for plant growth and ecological restoration in the rocky desertification areas in southwest China.Water consumption will increase year by year due to apple tree growth,so it is necessary to study the water use status of local apple trees and furtherly put forward some suggestions on water management.This study is also benefit for sustainable and healthy development of ecological industry in rocky desertification areas in a karst garben basin in southwest ChinaIn this study,a small typical karst depression in Dongshan karst mountainous area in Mengzi graben basin in Yunnan province was chosen as a study site.In this study site,hydrogen and oxygen stable isotope composition of soil water in different depth and xylem water of apple trees was determined,which was.used to quantitatively trace water source of apple trees by direct comparison、IsoSource model and MixSIAR model.The main results were showed below:(1)In 2018,the total rainfall in the study area was 829.8 mm.Rainfall amount and hydrogen and oxygen isotope of rainwater showed clear seasonal changes.In the dry season(November to April),rainfall was small with higher rainwater hydrogen and oxygen isotope.In the rainy season(May to October),the rainfall was obvious rich with lowet rainwater hydrogen and oxygen isotope values.There was a clear linear relationship between rainwater 8D and δ18O.The liner equation of 8D vs.δ8O in the study area was:δD=8.74δ18O+18.61,R2=0.97,N=60.The slope and intercept are larger than the global atmospheric precipitation line and China’s atmospheric precipitation line.The annual rainfall 8D and δ18δ values did not reflect the rainfall amount effect and temperature effect(2)The soil water content(SWC)in the study area had obvious temporal and spatial differences.In the temporal scale,the SWC at different depths showed greater values in the rainy season than in the dry season.In the spatial scale,the SWC in the most of sites decreased with increasing depth.The SWC in the middle and deep depths can only be replenished after a heavy rainfall event.The δD and δ18O values of soil water have obvious temporal and spatial changes In the time scale,the δD and δ18O in 0～10 cm soil water showed large and sensitive fluctuation with seasonal changes,higher in the dry season and lower in the rainy season.Although the 5D and δ180 values in 10～20 cm soil water showed similar variations to 0～10 cm soil water,the seasonal fluctuation in 10～20 cmsoil water was smaller than in 0～10 cm soil water.The δD andδ18O values in 20～40cm,40～60cm,and 60～80cm soil water showed slight changes.The δD andδ18O values in 80～100cm soil water showed relative steady staus.The δD and δ18O curve pattern in 0～10cm and 1 0～20 cm soil water was similar to rainfall,implying that soil water was recharged by rainfall throughout the year.The δD and δ18O curve pattern of soil water below 20cm depth was only similar to rainfall in rainy season,indicating that it was only recharged in rainy season In the spatial scale,the δD and δ18O values of soil water in February,April,and June showed a decreasing trend with soil depth increase,while the soil water in August and October showed an increasing trend with soil depth increase,which was mainly related to rainfall,evaporation,the mixing effect of soil water in different periods and the downward movement of soil water.(3)The water utilization ratio of apple trees to soil water in the three main growth stages were analyzed and calculated through direct comparison method,IsoSource model and MixSIAR model This study found that the MixSIAR model could show reasonable and complete calculated results Therefore,the results of the MixSIAR model were used to analyze the water source of apple trees It was found that apple trees during the budding period mainly consumed shallow soil water.The 0～10cm soil water was mainly water source for apple trees in east and west slope,with the utilization ratio of 62.6%and 81%,respectively.The 10-20cm soil water was mainly used water source for apple trees in the depression with the utilization ratio of 47.9%.However,during the flourishing new shoot period,the 0～10cm soil water was mainly water source for apple trees in the east,west and depression,with the utilization ratio of 38.5%,34.5%and 33.8%,respectively.During the fruit bulking period,the apple trees mainly utilized the deep soil water of 60～80cm and 80-100cm.According to the water use status of apple trees in the different growth period in the study area,this study think propose a specific water management suggestion that it should reduce the unproductive water consumption during the budding period and the extravagant water consumption of apple itself during the fruits bulking stage.This study provide a scientific basis for the sustainable and healthy development of ecological restoration industris in karst rocky desertification areas in southwest graben basin. |
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