Responses Of Stem Anatomical Traits Under Drought-rewatering Cycles Of Ginkgo Biloba L. And Their Seasonal Changes

Global climate change had led to frequent tree death,among which drought is an important factor.The purpose of this research is to study the response of phloem,cambium and xylem anatomical traits under drought-rewatering cycles of Ginkgo biloba L.saplings.In order to better understand the key anatomical traits of evaluating tree mortality and to accumulate the understanding of individual development and function,the changes of phloem,cambium and xylem anatomical structure of G.biloba saplings under drought and re-watering treatments and their seasonal characteristics were studied by making relevant tissue sections and microscopic observation.The main results are as follows:1.The lethal water potential of G.biloba saplings is close to P88(The xylem water potential when the xylem water conductivity lost 88%).2.The response of xylem pit aspiration rate and cambium geometry to drought was not obvious.With the increase of drought stress,the phloem and cambial cell vitality and the width of current year xylem decreased significantly.The thickness of pit membrane margo and torus decreased under drought,and their electron density increased.Drought would inhibit the activity of cambium in G.biloba.3.The phloem and cambium cell vitality and the thickness of the pit membrane torus and margo could be used as useful anatomical indicators for predicting mortality.4.Compared with the cambium cells of G.biloba,the phloem parenchyma cells had no obvious seasonal change,however,the collapse pattern of phloem sieve cells was more obvious.Generally,the sieve cells could not maintain functional in the early phloem of the current year growth season,while the sieve cells in the late phloem maintained functional throughout the year.5.In summer,the pit membrane began to develop,and in autumn and winter,it showed a relatively uniform electron density.Because G.biloba is a unique non-conifer gymnosperms in China,which is often used as ornamental plants,this research would be helpful to protect and utilize this tree species,increase the ecological conservation function of the region,and provide some information for the prediction of tree death under global drought stress.