| The Yuanmou dry-hot valley is a typical fragile area in China,with the defects of high temperature and drought stress,difficult ecological restoration,and the lag of socio-economic development.In the past,vegetation restoration projects focusing on planting Eucalyptus,Leucaena groves and other ecological tree species were carried out,but the plant diversity and ecosystem stability can not be guaranteed by a relatively single planting mode is,triggered to ecological effects limitation and a lack of economic benefits.Since the beginning of this century,in order to build a diversified ecosystem,the vegetation restoration strategy that combined“fruit forest”and“ecological forest”has been carried out in Yuanmou County.As a result,the vegetation coverage of the county reached 97.5%in 2019,an increase of 36.82%compared with 1999.The achieved significant results in vegetation restoration promote local economic development.However,dry and hot climate and moisture stress are still the main environmental factors restricting vegetation recovery in the area,such as the in 2012,dry and hot stress led to extensive withering and even death of plants caused by dry and hot stress in 2012.Therefore,it is particularly urgent to select drought-tolerance,highly effective and environmentally friendly tree as ecological restoration species in the region.Jatropha curcas L.,are considered as an ecological restoration species for alleviating the energy crisis because of its rapid growth,resistance and high oil content(biodiesel).In Yunnan province,it is mainly distributed in the Jinsha river,Lancang river,Nu river and Yuan river valleys with an altitude of 500-1930m.However,based on climate change and water balance,it is unclear whether the planting of Jatropha,an invasive species,reduces plant diversity,increases the aridity of the region and transfers its water mechanism to adapt the dry and hot environment.Therefore,this study takes the ecological recovery tree species of Yuanmou dry-hot valley as the research object.Based on the analysis of the climate and vegetation correlation,the researches on localized observation of evapotranspiration,rainfall redistribution and soil moisture in Jatropha woodland,high temperature and drought stress control experiments were conducted.Then the eco-hydrological process and the drought stress adaptation mechanism of Jatropha plantations were analyzed.To study whether it can be used as an ecological restoration species in the dry-heat valley,and the suitable ecological restoration area of it was found.The research results provide support for tree species selection and subsequent related research of ecological restoration in the area.The main results are as follows:(1)In this paper,the actual evapotranspiration of Jatropha plantation forest wasmeasured by the Bowen ratio energy balance method.The change patterns of evapotranspiration were as follows:sample plot 1(flat land)>sample plot 2(sloping land),wet season>dry season,and sunny day>rainy day.Taking the case in 2020 as an example,the rainfalls in the wet was 464.24mm and in dry seasons is 45.91 mm.And the actual evapotranspiration(ETBowen)in sample plot 1 and sample plot 2 were214.04mm and 182.18 mm in wet season,and 107.9mm and 95.94 mm in dry season,respectively.Therefore,the rainfall in wet season can supply enough water to meet the transpiration and evapotranspiration demand of Jatropha,instead,the actual evapotranspiration in dry season is greater than the rainfall.(2)After continuous observation of rainfall,it was found that the Jatropha forest canopy layer redistributed rainfall with 72.48%,4.60%and 22.92%of throughfall,stemflow and interception,respectively,and the critical rainfall amounts for producing throughfall and stemflow were 0.6 and 4.8 mm.In the future,the redistribution characteristics of rainfall by the canopy can be estimated via rainfall amount,rainfall duration and rainfall intensity.The intra-annual soil water storage changes in the Yuanmou dry-heat valley area are divided into three stages:soil water depletion period(October to December),soil water recovery period(June to September)and soil water relative stability period(January to May).Moreover,water was consumed in the dry season and stored in the wet season,with the largest amount of water stored in the 10-30 cm soil layer,followed by the 30-50 cm soil layer,but the largest amount of water consumed in the 50-75 cm soil layer.During the study period,the soil water storage in sample plot 1 and sample plot 2 were 39.32 and 16.58 mm.Planting Jatropha plays a significant role in soil and water conservation.(3)Both high temperature and drought stress reduced the photosynthetic characteristics and plant water potential of Jatropha leaves,which contribute to the water conductivity weakening of plants canopy and root system,water flow resistance increase and the inhibitions of its growth and total dry matter mass accumulation.However,plants can reduce the water absorption difficulty by regulating the water potential difference.adapted to drought stress.Drought stress is the main factor to lead the reduction of fluid flow volume.In the case of high temperature at noon,the fluid flow will decrease,forming a short“siesta”to reduce water loss.(4)The Jatropha plantation in Yuanmou dry-hot valley area is diverse and abundant in species.The species abundance of Jatropha community can reach 7.61.The stability of ecosystem functions is higher than that of Eucalyptus,Leucaena groves plantations and sparse shrubs.In other words,Jatropha is an eco-environmentally friendly tree species.In addition,taking into account the growth of Jatropha and the diversity of plant communities in tree and shrub layer and herb layer,the most suitable area,the more suitable area and the less suitable area for the restoration of it are within the range of elevation?1100 m and 10°<slope?15°,elevation?1100 m and slope>15°,elevation<1100 m and slope<10°.In conclusion,Jatropha plays an active role in climate regulation,soil and water conservation,water conservation and ecological restoration.It can be used as an eco-friendly tree species in the Yuanmou dry-heat valley area with high resistance to heat and drought stress,and can be planted for large-scale ecological restoration. |
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