| The evergreen and deciduous broadleaved mixed forest is the dominant vegetation type in the karst habitats in southwest China,which play an important role in maintaining the biodiversity and ecosystem functions.Leaf functional traits can reveal plants resource utilization and reflect the species adaptation strategies to the environment.Plant size and habitat factors can drive the variation of plant functional traits and thus affect plant strategies.However,it is unclear how assembled subcommunities of deciduous and evergreen plants adapt to resource-poor karst habitats in strategic and how adaptive strategy respond to changes in plant size and habitat factors.Therefore,this study established 53 20 m × 20 m forest plots in the typical karst mountain,and each plot was divided into four 10 m × 10 m quadrat plots by adjacent grid points,which totally contained 212 quadrat plots.We recorded plant species composition,leaf habits,plant individual numbers and habitat information of each plot according to the typical community survey method.Meanwhile,plants were modularized into different subcommunities according to leaf habit in each plot,namely this study including deciduous subcommunity and evergreen subcommunity;then we measured nine leaf functional traits of woody plants: including specific leaf area(SLA),leaf dry matter content(LDMC),leaf tissue density(LTD),leaf carbon(C),nitrogen(N),phosphorus(P)contents and their stoichiometric ratios(C/N,C/P,N/P);Plant size: including plant height(Height),diameter at breast height(DBH)and as well as including soil factors: soil organic carbon(SOC),soil total nitrogen(TN),soil total phosphorus(TP),rock exposure rate and soil depth.Leaf functional traits differentiation and strategy trade-off in evergreen and deciduous subcommunities were compared basing the community-weighted means(CWM),this study also evaluated the effects of plant size and habitat factors on woody plant leaf functional traits,as well as reveal the influencing of plant size and soil factors on the strategic differentiation of both subcommunities.It reveals the adaptation strategies and influencing factors of two subcommunities to resource-poor karst habitats,and provides theoretical support for species coexistence and karst degraded vegetation restoration.The main results are as follows:(1)The SLA and LDMC of the deciduous subcommunity were greater than the evergreen subcommunity;meanwhile,the leaf C,C/N and C/P ratios of the evergreen subcommunity were significantly higher than those of the deciduous subcommunity.However,the leaf N,P and N/P ratios of the deciduous subcommunity were significantly enhanced than the evergreen subcommunity.Moreover,both subcommunities showed significant negative correlations between SLA,leaf N and LTD,LDMC,signifying a leaf-economic trait trade-off in deciduous and evergreen subcommunities.Furthermore,Principal component analysis(PCA)on leaf functional traits specified the strategic differentiation mainly located at the side of the resource acquisition with high SLA and leaf N content for the deciduous subcommunity and situated at the side of the resource conservation with high LDMC and LTD for the evergreen subcommunity.(2)Plant size can independently regulate the expression of leaf functional traits in karst woody plants.Plant size is positively correlated with SLA,leaf C/P and N/P ratios,but negatively correlated with LDMC,LTD,leaf C content.Meanwhile,plant size had different effects on leaf functional traits of woody subcommunities with different leaf habits,and deciduous subcommunities were more significantly affected by plant size,SLA,LDMC,LTD and leaf C and N contents,as well as leaf C/N 、C/P and N/P ratios of deciduous subcommunity were significantly correlated with plant size,while,leaf N content and C/N ratio of evergreen subcommunity were significantly correlated with plant size.(3)Soil factors could independently affect the variation of leaf functional traits of woody plants in the karst evergreen and deciduous broadleaved mixed forest.Soil depth was the most important soil factors,followed by soil TP,and soil SOC and rock exposure had little effect,while soil TN had no significant effect on leaf functional traits.In addition,there was different response of woody plant subcommunities with different leaf habits to changing in habitat factors.Soil TP was the most important soil factor affecting leaf functional traits of evergreen subcommunities,followed by rock exposure rate,soil depth and soil TN,while soil SOC had no significant effect.Soil depth was the most important soil factor affecting leaf functional traits of deciduous subcommunities,followed by soil TP and rock exposure rate,while soil SOC and TN had no significant effect.(4)Plant size and soil factors promote leaf trait differentiation and strategy trade-off of deciduous and evergreen subcommunities in karst habitats.The thicker soil depth and more fertile soil promoted rapid resource acquisition of deciduous subcommunities with larger plant size,while the shallower soil depth and poor soil resources promoted resource conservation of evergreen subcommunities with smaller plant size.Strategic differentiation among species promotes niche differentiation and reduces the intensity of interspecific competition,which maximizes the utilization of restricted resources in karst habitats and promotes better species coexistence.The effects of plant size and soil factors on the strategy differentiation of different leaf ecological habits will provide theoretical support for the restoration of degraded karst forest vegetation.Overall,deciduous and evergreen subcommunities achieved the best balance between resource acquisition and conservation in the subtropical karst mixed forest vegetation,and the evergreen subcommunity was resource conservation while the deciduous subcommunity was resource rapid acquisition.Plant size and soil factors promoted the strategic differentiation of different leaf habit subcommunities,that is,the conservation strategy of the small evergreen subcommunity in the shallow soil with poor resources,and the rapid resource acquisition strategy of the large deciduous subcommunity in the rich and thick soil depth. |
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