Water Migration Process And Mechanism Of Typical Plantation Forest In Central Hubei, China

Water is an important factor limiting plant growth.In China’s subtropical regions,global climate change had led to frequent seasonal droughts,and the large-scale plantation of Pinus massoniana Lamb.and Cunninghamia lanceolata(Lamb.)Hook.in the low hills of southern China in the last century had led to ecological problems such as reduced biodiversity,decreased productivity,and serious pests and diseases.Faced with the dual constraints of fragile forest ecosystems due to plantation management patterns and severe seasonal droughts due to climatic characteristics,it is unclear how the process of water migration mechanisms in plantation forest ecosystems and their plant water use strategies will change and how the adaptability of forest ecosystems will change.In this study,four typical plantation forests in the Taizishan Mountain area of Hubei Province,China were used:Pinus massoniana Lamb.coniferous pure forest,Cunninghamia lanceolata(Lamb.)Hook.coniferous pure forest,Quercus acutissima Carr.broadleaf pure forest and Cupressus funebris Endl.and Ilex corallina Franch.mixed forest Based on the hydrogen and oxygen isotope compositions of water bodies before and after the dry and wet seasons and different levels of precipitation,and combined with the Mix SIAR model and ANOVA,we systematically elucidated the stable isotope characteristics of atmospheric precipitation and the sources of water vapor in the region.The study also quantitatively elucidated the water infiltration process of soil water and the water use pattern of typical plants in the dry and wet seasons and at different time scales of precipitation,and preliminarily revealed the water migration mechanism in the plantation ecosystem.The main results of this study are as follows.(1)The slope and intercept of atmospheric water line equation(LMWL)of the Taizishan Mountain area were extremely close to the global atmospheric water line,indicating the complexity of water vapor sources in the study area and its climatic typicality.The stable hydrogen-oxygen isotope values and excess deuterium(d-value)in precipitation had relatively obvious seasonal variations;there were obvious differences between the sources of water vapor in the wet and dry seasons in the study area,where the water vapor air masses of atmospheric precipitation in the wet season mainly originated from the Indian Ocean and the western Pacific Ocean,and those in the dry season mainly originated from the cold and dry interior of the Asian and European continents(Russia and Mongolia).(2)Among the four typical man-made forests in the Taizishan Mountain area,the canopy retention and deadfall retention effects of broadleaf pure forests were the best,and the broadleaf pure forests had better regulation of the precipitation redistribution process in forest ecosystems,followed by mixed coniferous forests,and the least coniferous pure forests,which may be due to the fact that the depression of broadleaf pure forests in this study area was greater than that of mixed forests and coniferous pure forests.(3)The value of soil water in the surface layer of the study area was most obviously influenced by precipitation .With the increase of soil depth,the value of soil water was gradually reduced by precipitation,and the response to rainfall was slower;with the increase of rainfall magnitude,the response of the value of soil water to precipitation was faster,and the influence of precipitation on the value of soil water in the deep layer was greater.The broad-leaved and mixed forests could accept new precipitation signals while retaining the previous precipitation signals,and their soils had stronger water holding capacity,while the soil water isotope values of coniferous forest soils varied more before and after rainfall,indicating their stronger drainage capacity.In the infiltration process of precipitation in different forest sites,rainfall in coniferous forest(P.massoniana,C.lanceolata)soil mainly infiltrated in the form of mixing and diffusion with old soil water before rainfall,while in broad-leaved forest(Q.acutissima)and mixed forest(C.funebris and I.corallina)soil mainly infiltrated in the form of repelling old soil water before rainfall.(4)The direct water source of plant water in the Taizishan Mountain area was soil water.The response of I.corallina to precipitation was relatively rapid,while there was a lag in the use of precipitation by P.massoniana,C.lanceolata,Q.acutissima,C.funebris and the larger the rainfall level,the shorter the lag time.I.corallina mainly utilized surface and shallow soil water under different moisture conditions;while P.massoniana,C.lanceolata,Q.acutissima and C.funebris could flexibly switch water sources under different moisture conditions,indicating the existence of significant functional dimorphic characteristics of their root systems.(5)In mixed forest,C.funebris and I.corallina competed for water to a certain extent in the wet season when water was abundant and when the soil moisture content was high before rain,but there was less competition for water in the dry season when water was deficient and when the soil moisture content was low before rain.Mixing the two can effectively avoid water conflicts in the dry season when water is deficient.This study found that the soil water-holding capacity and the regulation of rainfall distribution process of broad-leaved forest and mixed coniferous forest are better than those of pure coniferous forest in Taizi Mountain area of Central Hubei,and they had better coping ability when facing the constraints of fragile forest ecosystem and seasonal drought in Central Hubei.In the future reconstruction and transformation of plantation forest in Central Hubei,we can consider mixing coniferous species of C.funebris with broad-leaved native species of I.corallina,which can effectively avoid water conflicts during the dry season when water is scarce and help maintain the stability of the regional forest ecosystem to a certain extent.