The Relationship Between Efficiency And Safety Of Xylem Anatomical Structure Of Typical Tree Species In Tianmu Mountain

Vegetation drought-induced decline and even death,is not confined to arid or semi-arid regions.Trees in humid areas are more likely to die due to drought caused by climate change.Xylem hydraulic function(including hydraulic efficiency and safety)is the core of drought-induced mortality mechanism,while anatomical is the basis of function.Therefore,establishing quantitative relationship between xylem anatomical and functional of woody plants is the key to solve the drought-induced mortality mechanism for plants in humid areasand realising the“efficiency-safety”trade-off of their xylem.In this paper,woody angiosperms and gymnosperms in humid regions were compared to study their xylem“efficient-safety”tradeoffs and anatomical differentiation in artificial and natural habitats.Artificial habitats:Ligustrum lucidum,Quercus glauca,Acer buergerianum,Michelia maudiae;Podocarpus macrophyllus var.maki,P.macrophyllus,Pseudolarix amabilis,Cunninghamia lanceolate,Cedrus deodara.Natural habitats:L.lucidum,Q.glauca,A.buergerianum,Daphniphyllum macropodum;P.amabilis,C.lanceolate,C.deodara,Cryptomeria japonica,Picea asperata.Among them,angiosperms privet,cypress,acer trigoni;Gymnosperms,Chinese fir and Cedar are common species in two habitats.In this study,water conductivity and other parameters were obtained by pressure chamber method and vulnerability curve was constructed.Anatomical structure parameters were obtained and measured by saffron-solid green dyeing method and optical microscope.The main results were bellows:(1)Hydraulic function of xylem:In the same habitat,angiosperms hydraulic efficiencywas higher than gymnosperms but embolism resistance was lower than gymnosperms,especially in the natural habitat,there was a significant difference in hydraulic efficiency(P<0.05).In the two habitats,the hydraulic efficiency of common species in artificial habitat was significantly lower than that in the natural habitat(P<0.05),but the embolism resistance was significantly higher than that in the natural habitat.(2)There was a cooperative relationship between the xylem vessel structure and the anatomical structure at the pit level.The results showed that the vessel(tracheid)diameter and hydraulic diameter were significantly negatively correlated with the vessel(tracheid)density,and positively correlated with the pit structure.(3)Xylem"efficiecy-safety"tradeoff:With the exception of evergreen angiosperms in natural habitat,there was no efficient-safety tradeoff of other species.It caused by the difference in xylem structural traits.The reason for the absence of tradeoff between efficiency and safety of xylem may be that the anatomical structure may not necessarily reduce the safety while improving the efficiency.(4)The anatomical-function relationship of xylem:The existence of functional trade-off was determined by its anatomical structure:K_s and P₅₀ have different structural requirements(there was an efficiency safety trade-off),while K_sand P₅₀ had similar structural requirements(no efficiency safety trade-off).In addition,the hydraulic diameter,vessel wall thickness and vessel density had the most significant influence on the hydraulic function of all species in this study.Hydraulic efficiency and embolism resistance are the comprehensive functions of xylem as a complex network for hydraulic system different water utilization strategies of common species in different habitats,and the hydraulic functions are coordinated with the structural properties.Secondly,redundancy analysis results show that xylem structure contributes independently to efficiency and safety,and hydraulic efficiency and embolism resistance have different structure requirements,resulting in the failure of functional efficiency-safety tradeoff.