Study On Drought Resistance Assessment And Adaptive Mechanisma Of Alfalfa In Drought Stress

21 foreign alfalfa were selected as experiment marterials in this paper,screening out strong drought-resistanct marterials and analyzing physiological and biochemical characters,taking directly evaluate on survival and indirectly comprehensive evaluate on a number of morphlogical characters as method.and systematically studied drought-resistant ability of alfalfa under water stress and water stress on the physiological and biochemical changes.To identify and evaluate alfalfa drought-resistant properties,and further enrich the evaluation content of drought-resistant ability of alfalfa resource and provide the scientific basis for the planting,breeding and introduction of drought-resistance of alfalfa.Determination indicators include:suvival,plant height,leaf length and leaf width,aboveground biomass,and other forms stress indicators index;leaf relative water content and natural saturantion deficit;proline content soluble sugar centent and the relative conductitvity,MDApotective enzymes SOD,POD,CAT activity chlrophyll content,the net photosynthetic rate stomatal conductance,transpiration rate,the intercellular CO₂ concentration atmospheric CO₂ concentration(Ci) and(Ca) ratio of photosynetictic characteristics indicators.ABA,IAA,GA₃,ZR leaves hormone centent of the main findings are as follows:(1) The strong drought-resistance of the material are ZXY04P-44,ZXY04P-10,ZXY04P-32.(2) Blade length,blade width,dry matter content stress index,shoot than stress index,belowground biomass stress index can be used as indenrification of comprihensive evaluation index of drought-resistance of alfalfa.(3) The 3 water saturation dificit of alfalfa leaves have increased.The strong drought-resistant alfalfa increase small,and the weak drought-resisitant alfalfa increase great.The two kingds of major osmolyte of 3 alfalfa represent upward trend.The total gradually incerase.This indicates that alfalfa can adapt to the arid environment by osmoregulation.But the osmoregulation is limited (4) The content of malondialdehyde and injury rate of 3 material increased under water stress,indicated that the balance between the accumulation of oxygen and cleanup has been destroyed.Thereinto,the strong drought-resistant ZXY04P-44＞the weak drought-resistant ZXY04P-310,indicated that under the same extent of the membrane is drought-resistant ZXY04P-44＞the weak drought-resistant ZXY04P-310.(5) water stress,the ability of preventing the membrane lipid peroxidation and maintaining the integrity of the membrane is drought-resistant ZXY04P-44＞the weak drought-resistant ZXY04P-310.(6) SOD activity present the same trend in basically—firstly increased and then droped,that indicated SOD.(7) activity increased induced by moderate water stress.H₂O₂ generated by SOD super-oxide anion inevitable increased.Although the changed trend of POD and CAT activity first trend and then drop,strong drought-resistanct marterial ZXY04P-44,two enzyme are high activity and more sensitive to water stress,and materials ZXY04P-467take sencond place.As the worst drought-resistance of materials ZXY04P-310,the activity of both is low and reflect slow on the water stress.One of the drought-resistant materials is ZXY04P-310,three kinds of enzyme represent strong synergies.There is a certain scope from three protective enzyme activity,and can not be suffered from severe water stress by endless.(8) Pn,E,Gs droped deeply under water stress,wue represents a declining trend.The value of Ci/Ca is not significant difference between water stress and materials.But three materials perform the same rule,that is first drop and then advance.Thereinto the weak drought-resistance is more sensitive to water stress and change faster than the strong drought-resistance.The stomatal limitation under mildly water stress is the main factor that reduce photosynthesis of three kinds of alfalfa.However,under moderate and severe water stress,Pn decrease is mainly by the decline of mesophyll cell,non-stomatal limitation plays a major role.(9) This experiment indicated that with increasing degree of water stress,other indicators have all decreased except the value of AA,ABAå’ŒABA/(IAA+ZR+GA₃) which gradually increased.However,with the condition of severe drought,the ability of drought-resistant alfalfa directly withstand water stress is stronger than poor drought-resistant alfalfa.3 alfalfa in the mild water stress hormone under the coordination between four to inhibit the growth of direction,and severe in the direction toward promoting growth,and ZXY04P-44 to promote stronger growth trend.To sum up,when drought-resistant alfalfa is under water stress,the water metabolism,osmolyte,cell membrane permeability,membtanaceous peroxide system,the protection system of photosynethetic systems,as well as the changes in hormones are conductive to raising the ability of resisting drought,this may be a factor that drought-resistant alfalfa can survival in the extreme environment of high temperature,and produce a greater biomass.