Water Source Of Camellia Oleifera Forest In Hilly Region Of Southern China Based On Hydrogen And Oxygen Isotopes

The southern hilly region is one of the most suitable cultivation areas for Camellia oleifera due to its multi-micro acidic red soil and abundant hydrothermal resources.However,seasonal drought seriously affects the ecological sustainable development of C.oleifera forest.Quantifying the water uptake source of Camellia oleracea is of great significance for optimizing the water management mode,perfecting the spatial configuration of C.oleifera and alleviating the seasonal drought.In this paper,Isotope tracer technique is applied,combined with the linear mixed model and bayesian model.Analyze the dynamic law of soil moisture and conduct quantitative analysis C.oleifera root water uptake source in C.oleifera forestry in the southern hilly region during the test period（April 2019-October 2020）.And then discusses the C.oleifera forest water use strategy.The optimal model of quantifying water source of C.oleifera in hilly region was selected.To achieve the optimal allocation of the forest region of water resources and promote forestry ecological development provides a scientific evidence.The main results are summarized as the following:（1）The δD of precipitation,soil water and xylem water in C.oleifera forest in hilly region ranged from-150.12 to 12.55‰,-100.10 to-0.49‰and-82.94 to-9.2‰,respectively.The change of the deltaδ¹⁸O range respectively-19.97～0.03‰,13.15～1.07‰and 11.36～1.72‰.The results of d-excess and HYSPLIT showed that the main sources of rain water vapor in C.oleifera forest showed a cyclic variation pattern of"continental air mass"--"Marine air mass"--"continental air mass".The deuterium deviationδD of C.oleifera leaves was negatively correlated with transpiration rate,and the regression equation was Tr=-0.02Δ_d+1.20（R²=0.64）.Compared with the water isotope of C.oleifera,the xylem water of C.oleifera is basically close to the soil water isotope,indicating that there is no isotopic fractionation in the xylem of C.oleifera in hilly areas,and the soil water in 0～60 cm layer is mainly used,the mixed precipitation and soil water are less directly used.（2）he results of linear mixing model showed that the utilization ratio of C.oleifera to soil water in 0～30,30～60 and 60～100 cm soil layer was 70.3%,18.6%and 11.1%,respectively.And the utilization ratio of Mix SIAR was 56.1%,21.6%and 22.3%,respectively.C.oleifera has high plasticity and adaptability to water use,and water use strategy can be adjusted timely according to different environments.In spring and summer,when precipitation is concentrated,C.oleifera mainly uses soil water in 0～30 cm soil layer.In autumn,with the decrease of precipitation,the ratio of C.oleifera to soil water in 0～30 cm soil layer gradually decreases,while that in 30～100 cm soil layer increases.（3）Both linear mixing model and Bayes Mix SIAR are suitable for quantifying the main water sources of young C.oleifera in the hilly region of southern China.However,the calculation results of Mix SIAR are more accurate,so Mix SIAR is recommended to quantify the water sources of C.oleifera in the hilly region of southern China.53.5%,53.3%and 52.2%of water in the first,second and third fruit growth peak of C.oleifera came from 0～30 cm soil layer,and the contribution of the other two soil layers to C.oleifera was 14.3% to 26.4%,according to MixSIAR.