Water Use Strategies Of Pinus Yunnanensis Under Different Restoration Patterns In Haifeng Karst Slopes,East Yunnan

In order to explore the water adaptability of Pinus yunnanensis to karst habitat during the long-term restoration process,this paper took Pinus yunnanensis community in different restoration modes in karst rocky desertification slope area of Haifeng in eastern Yunnan province as the research object by using stable isotope technique as the main research method,the differences and influencing factors of water use strategies of pinus yunnanensis communities in different restoration modes and habitats have important guiding significance for promoting vegetation restoration,improving karst ecological environment and enhancing forest ecosystem productivity.The main conclusions are as follows:(1)The soil water supply of vegetation community was different in different seasons.The recharge of soil water in dry season mainly comes from groundwater,which belongs to spring(surface karst groundwater)nourishment type.In rainy season,soil water mainly comes from rain and belongs to rainfed type.In the succession stage from pure forest of Pinus yunnanensis to secondary forest of Pinus yunnanensis,the utilization of deep soil water by mature Pinus yunnanensis decreased from 60.8%to40%,and the utilization ratio of deep soil water decreased.The function of water-bearing structure layer in karst surface zone recovered with vegetation restoration,and the water conservation function was improved.The water acquisition patterns of natural secondary forest of Pinus yunnanensis,artificial mixed forest of Pinus yunnanensis and pure forest of Pinus yunnanensis were dominated by fissure,dominated by shallow+middle soil water,dominated by deep soil water.The water acquisition pattern of primary forest of Castanopsis orthacantha in the reference plot belongs to comprehensive type,while that shrub of Myrsine africannais dominated by shallow soil water.(2)The?¹³C of leaves fluctuated in dry season and rainy season,and the?¹³C of leaves in rainy season was greater than that in dry season.Three kinds of Pinus yunnanensis forest,the?¹³C of natural recovery of the Pinus yunnanensis forest was the largest(-27.43‰),and the WUE was the highest.The?¹³C of pure forest of Pinus yunnanensis was the lowest(-28.19‰),and the WUE was the lowest.In the control group,the?¹³C of primary forest of Castanopsis orthacantha was-27.05‰,which was higher than that of three Pinus yunnanensis forest.The?¹³C of shrub of Myrsine africannais was lower than that of the three Pinus yunnanensis forests,and the drought resistance was the weakest.The results of cluster analysis showed that the primary forest of Castanopsis orthacantha,natural secondary forest of Pinus yunnanensis and artificial mixed forest of Pinus yunnanensis belonged to high WUE community,pure forest of Pinus yunnanensis belonged to medium WUE community,and shrub of Myrsine africannais belonged to low WUE community.In general,plant water use efficiency and drought resistance increased with the positive succession of vegetation community.(3)The characteristics of soil hydrological function were different with different vegetation restoration years,restoration modes and habitats.In general,the soil hydrological function of the secondary forest of Pinus yunnanensis was better than that of the artificial mixed forest of Pinus yunnanensis and pure forest of Pinus yunnanensis,and the water and fertilizer conservation capacity of the fissured habitat was better than that of the soil surface and soil slope.With vegetation restoration,the increase of soil layer thickness and forest canopy coverage can effectively mitigate the impact of precipitation,increase the water storage function of litter layer,improve soil structure,and gradually recover soil hydrological function.However,some nutrient contents do not completely increase with the increase of vegetation succession level in the process of vegetation restoration.(4)The differences of plant water strategies were mainly influenced by plant factors and soil factors.Effects of root density,DBH and leaf C/P were the main factors affecting plant factors;Soil water content,large aggregate,sand,soil C/N and soil TN were the main factors affecting soil factors.In different seasons,the main influencing factors of WUE were different.In rainy season,leaf C/P,soil C/N and sand were the main influencing factors.In the dry season,root density,soil water content,large particle aggregate,DBH and soil TN were the main influencing factors.(5)By building the plant water use strategy pattern sketch sums up the crack+soil water comprehensive,the leading,shallow+middle soil water leading sources for pattern,community on water use efficiency is high;deep soil water leading water access mode,water use efficiency is only second to former;shallow soil water dominant community,water use efficiency is low,drought-resistant ability is the weakest.In the long-term restoration process,plant intermixing pattern and fissure habitat can promote vegetation restoration.In the soil slope habitat of pure forest of Pinus yunnanensis,mixing with Myrsine africanna and Cornus paucinervis can increase the vertical structure of tree+shrub,slow down soil surface loss and increase soil water content.In the soil hole habitat of shrub of Myrsine africannais,increasing the tree layer,Castanopsis orthacantha,Lithocarous dealbatus,mature Pinus yunnanensis and Keteleeria evelyniana,Pinus armandii belong to the high water use efficiency plants,which can promote vegetation restoration and improve the ecosystem function.