The Difference Of Xylem Structure And Hydraulic Function Of Three Taxodiaceae Species

Global climate change research generally agrees that temperatures on the earth's surface will rise and precipitation patterns will shift,leading to more frequent and intense droughts.The impact of climate change on plants and the adaptation of plants to environmental changes have attracted the attention of botanists and ecologists.The phenomenon of withering and death of plants due to drought stress is not limited to arid and semi-arid areas.In humid forests,the drought consequences may be more serious due to poor drought-resistance adaptability.When the water availability changes,the hydraulic system of plant branches and root system will respond and balance,thus forming an adaptation strategy,namely“efficiency-safety”trade-off.Quantifying the water transport and embolism resistance of branches and roots in wetting regions,and revealing their adaptive strategies,is helpful to understand the water adaptation mechanism of species in wetting regions.In this study,Sequoia Sempervirens,Taxodium Ascendens and Taxodium Distichum grown in homogenous gardens were selected as research objects to compare the differences of hydraulic function traits and xylem structure traits between branches and roots,as well as the quantitative relationship between the structural traits and the functional traits of xylem.In addition,the response of the hydraulic system structure(tracheid area,tracheid diameter,tracheid wall thickness,tracheid density,etc.)to temperature change was also discussed in T.distichum.(The preliminary experimental results showed that in the three Taxodiaceae plants,the correlation between multiple indexes of the anatomical structure in T.Distichum and temperature was higher than 0.9,and R² was greater than 0.87,which was significantly higher than that of the other two species.)The results showed that:(1)Compared with branches,roots had higher hydraulic conductivity and weaker embolism resistance(hydraulic conductivity,K_S,of roots were higher than that of branches,and embolism resistance,P₅₀,of branches were more negative than that of roots).(2)The correlation coefficient between branch K_S and branch P₅₀ of the three species was close to0(R²=0.02,P=0.37),and the correlation coefficient between root K_S and root P₅₀ was 0.07(R²=0.07,P=0.09),indicating that there was no efficiency-safety tradeoff in the cross-species branch hydraulic conducting system,and a weak but not significant trade-off relationship between root hydraulic conducting system.(3)Different xylem anatomical structures are used to determine K_S and P₅₀ of branches and roots in the three tree species.That is to say,there is no efficiency-safety trade-off in xylem hydraulic conducting system of branches and roots,as the material basis for this trade-off does not exist.(4)The response of xylem structure to temperature shows that the temperature in May can be used as a reconstruction climate factor to obtain a more accurate reconstruction climate sequence.The tracheid area,average diameter,maximum diameter and wall thickness of tracheid are sensitive to temperature,which can be used as a“temperature indicator”for the study of tree wheel climatology.This study quantified the water transport capacity and embolism resistance of branch and root xylem,revealed the trade-off strategy of water transport between branch and root xylem of tree species in humid area,provided experimental basis for seed selection and breeding of vegetation plantation in humid area,and also provided basic data of relevant modules for the improvement of global climate vegetation prediction model.