Study On The Resource Cultivation Of Two Rock Elm Tree Species And Their Drought & Salt-resistance Characteristics

This paper overviews the studied states quo of photosynthesis,physiological and biochemical characteristics for some plants under saltstress and waterstress, based on this,we proceeded to have the seedling-bred experiment on Ulmus pumila in China,Ulmus thomasii and U.crassifolia from the United States,under the greenhouse condition three kinds of one-year seedlings were proceeded the plant-potted experiment through salt-and-water control,physiological and biochemical indexs reflecting salt-and-drought resistence were periodically measured,then analyzed,finally synthesized to assess them.the findings are as follows:1.In the course of seedling-bred experiment,height growth,ground diameter growth,anti-disease-and-insect ability of three trees above were respectively measured,the research showed:the growth amount of ground diameter and the ability of outside power-resistence of roots for one-year Ulmus thomasii and U. crassifolia outgrew in China,but their height growth and the ability of control to some diseases and pests were more interior,buds sprouting,seed budding,and autumn defoliage time were put off from two to three weeks or so,compared with U.pumila;the survival rates of those contolled cuttings with 500 ppm ABT1 are greatest,reforestation experiments show that the height growth of U.thomasii and U. crassifolia is faster than that of Sang orange and U.pumila early,but no less than Zelkova schneideriana and pteroceltis tatarinowii.2.Researches on both Photosynthesis and chlorophyll fluorescence parameters show:1).Daily changes of Pn and Tr about U.thomasii and U.crassifolia,are one-peaked curve,but the appearing time and the size of peak value are different. Leaves' Pn & Tr of different parts in the same plant also have differences - Pn: middle leaf＞top leaf＞basal leaf;Tr:middle leaf＞basal leaves＞top leaf.Daily changes Of leaf WUE in the different parts of two tree species are one-peaked curve with unilateral dropping,for U.crassifolia,WUEs in basal leaves and middle leaf are lower than the top leaves';for U.thomasii WUEs in middle leaf and top leaf are higher than basal leaves;3)In Spring,daily changes of maximal fluorescence (Fm)from five tree species,such as U.gaussenii cheng,U.Crassifolia,Pistacia chinensis Bunge,Z.schneideriana,and U.thomasii,are basically similar,"M"-type double-peak curve.In three other seasons,daily changes of Fm of the five species express a "V"-shaped curve,ΦPSâ…¡,PSâ…¡potential activity(Fv/Fo)of Five species, show "V"-shaped curve,and their lowest values appear at 2:00,noon.4).Among Spring,Autumn and winter,daily changes of PSâ…¡non-cyclic electron transfer rate ETR,and NPQ from the five species show similar trends,a "∧" one-peak curve. In Spring,daily changes of QP show a"V"-shaped curve,in summer,a "∧" font-peak curve,daily Changes of qP in trends in autumn,are inconsistent.3.During water stress the potted elm seedlings of three kinds above were respectively proceeded.The physiology indexs measured periodically included Pro, dissolubility sugar,MDA,chlorophyll content,electric conductivity,survival rate, CAT activity,soil water content and leaf water content under water stress,and photosynthesis some time in the fields etc.the results obtained by the experiment indicated that:1)with the prolong of waterstress time,Pro,MDA,CAT activity and ds inside leaves of three kinds of elms all went up,the electric conductivity showed the aggrandized trend,the chlorophyll content,and net photosynthesis were reported to descend,and the descent of survival ratio was rather obvious.4.During salt stress,the results showed:l)along with the exaltation of salt density and the prolong of stress time,pro,MDA and SS inside tree leaves of 5 kinds all went up,electric conductivity was reported the aggrandized trend,decomposition of Chl accelerates,X content,Pn,and SR all have a downward trend.2)Fresh (dry)biomass weight,total leaf area,single leaf area,fresh weight,dry weight,leaf area ratio,leaf thickness of the five species,express a downward trend with the increase of salt concentration and the extension of stress time.3)Under salt stress,the ratio of crown to root such as U.gaussenii,U.crassifolia,and Pistacia chinensis has a downward trend,that of Z.schneideriana has an upward trend,and that of U. thomasii almost changes;4)with the the prolong of salt-stress time,changing laws of SOD,POD,SS,and SP in five tree species are not consistent;5)With the increase of salt concentration,the inhibited degree of height growth was up,and the prolong of stress time,the gap between controls is gradually increasing.Stress symptoms of leaves along with salt concentration and time also have such effects.Under salt stress inhibited degree of height growth and victimed symptoms of 5 tree species can also reflect differences on salt tolerance.6)With the extension of salt stress,the total contents of Na⁺ in U.crassifolia,U.thomasii and Z.schneideriana increase with the increase of salt concentration.Na⁺ contents in U.gaussenii and Pistacia chinensis don't express a single change in the trend.Under Salt stress,Na+ contents in roots are most,less,lest,in leaves.Leaves are the main injury location of U.gaussenii, Z.schneideriana and Pistacia chinensis by salt,and roots and stems are the main injury location of U.thomasii and U.Crassifolia.7)On the whole,salt stress reduce K⁺ / Na⁺ value in upper leaf,but for U.crassifolia and Pistacia chinensis the changing laws of K⁺ / Na⁺ value in upper leaves are not obvious;the impacts of salt stress on the Ca²⁺/ Na⁺ are different among 5 tree species,the Ca²⁺/ Na⁺ in U. gaussenii,U.thomasii,and Z.schneideriana goes up a little under lower salt concentrations,afterwards reduces with the increasing of salt gradient,but the changing laws of Ca²⁺/ Na⁺ value in Pistacia chinensis and U.crassifolia aren't obvious.8)under salt stress principal component analysis of individual height and physio-biochemical indicators in different tree species show that:among 5 tree species the cumulative contributions of the first,second and third principal components reach more than 75 percent,the first principal component of U.gaussenii shows that the impacts salt stress on its Chl,Chlb,Chla and REC are greater;the first principal component of U.thomasii shows that the impacts salt stress on its REC,SS,MDA are greater;the first principal component of U.crassifolia shows that the impacts salt stress on its REC,RWC and X.are greater;the first principal component of Z.schneideriana shows that the impacts salt stress on its REC,Chlb and Chl are greater;the first principal component of Pistacia chinensis shows that the impacts salt stress on its Chla,Chlb and Chl are greater.9)Research on Ultrastructure of mesophyll cells shows that:under NaCl stress the leaf thickness of Pistacia chinensis,U.crassifolia,and U.thomasii significantly increases,but the leaf thickness of U.gaussenii and Z.schneideriana is thinning.At the same time spongy parenchyma cells of Pistacia chinensis,U.crassifolia,and U.thomasii become more, and the cell shape comes to be like palisade,leaves have the trend of the evolution towards a kind of leaf whose length and width are the same,this may increase the number of chloroplast,greatly improve photosynthetic efficiency and yield more organics to withstand adverse persecution,but chlorophyll contents in Z.schneideriana and U.gaussenii decrease relatively.Finally 11 indices such as Chl,Pro,MP,MDA,Pn,SS,SR,SOD,POD,X,and SP were elected from those studied ones,and the salt-tolerant abilities of five tree species were assessed by membership function evaluation,the salt-tolerant order of assessment:U.crassifolia,U.thomasii＞Pistacia chinensis＞U.gaussenii＞Z.schneideriana.on the other hand,anti-drought abilities of U.crassifolia and U. thomasii are all stronger than that of U.pumila.Based on this,the conclusion was drawn that the drought tolerance of three varieties was in the order of U. thomasii＞U.crassifolia＞U.pumila.Therefore,both U.thomasii and U.crassifolia may be introduced to cultivate in China,especially act as the first reference to ecosystem type in the limestone mountain areas and saline with salt content from 0.3 percent to 0.5 percent.