Screening Of Waterlogging Tolerance Of Alfalfa And The Role Of NO In Alleviating Waterlogging Stress

Alfalfa(Medicagosativa L.)js a perennial herbaceous legume forage and is one of the most important legume forages of the world.Due to the poor submergence tolerance ability of alfalfa.it's difficult to cultivate alfalfa with high quality in southern china.Nowadays,with increasing demands of forage,the cultivation of submergence resistant alfalfa in southern region is a urgent problem need to be settled down.This study chose 20 different varieties of alfalfa as experimental material to determinate their morphological and physiological differences under the submergence stress.According to these morphological and physiological indicators,the comprehensive function evaluation of submergence resistance was carried out by using membership function method.What's more,we investigate the methods to strengthen the submergence tolerance ability of alfalfa through exogenous nitric oxide(NO)and ammonium nitrate.The results are listed as follows:1.The submergence stress experiment showed that the growth of alfalfa was significantly inhibited after 15 days submergence treatment.The plant height,root length,fresh weight,stem fresh weight and leaf fresh weight of 20 alfalfa varieties were decreased compared to control group.The MDA contents were increased and the soluble protein contents were decreased due to the treatment.The activities of SOD enzyme increased to defend the lipid peroxidation.There is no obviously difference in soluble sugar content of alfalfa.We evaluate comprehensively the submergence tolerance ability of alfalfa with membership function analysis method.We found that multi-leaf Huaiyin(0.78)and NO.4 Huaiyang(0.74)were better than the others in submergence tolerance ability.WL 712(0.15),WL903(0.26)and NO.5 Gannong(0.21)were sensitive to submergence treatment.2.In the experiment of adding exogenous NO,it was found that the addition of NO can effectively promote the root growth of alfalfa under submergence stress.The relative content of chlorophyll increased,which alleviated the damage of PSII caused by submergence stress.However,the growth of aboveground parts and the accumulation of biomass decreased.This provides a basis for the rapid growth of alfalfa in the next process.During the process of recovering,NO can increase the relative chlorophyll content and chlorophyll fluorescence performance of alfalfa,alleviate the damage of PSII function,increase Fm and Fv/Fm,and promote the growth and biomass accumulation of alfalfa above and below.3.In the experiment of adding exogenous ammonium nitrate,it was found that ammonium nitrate reduced the specific energy flux by increasing the chlorophyll content of alfalfa,the fluorescence quantum yield and efficiency of chlorophyll A under submergence stress.The addition of ammonium nitrate improves the fluorescence performance index,alleviates the damage of the photosynthetic original components of alfalfa,and reduces the photosynthetic energy dissipation as heat energy.The maximum photosynthetic efficiency and actual photosynthetic efficiency of alfalfa were increased due to the photochemical quenching ratio rose.In addition,the submergence stress had the most obvious effect on the elements in the leaves of alfalfa,which significantly reduced the contents of K,Ca,Mg,P,Cu and Zn in the leaves of alfalfa,and also significantly increased the contents of Na and Mn.However,the addition of ammonium nitrate significantly reduced the Mn content of alfalfa.In summary,we conducted a comprehensive evaluation of the submergence resistance abilities of 20 different varieties of alfalfa,and selected the submerge-tolerant and submerge-sensitive varieties.Moreover,we found that addition of exogenous NO and ammonium nitrate can improve the submergence resistance of alfalfa.It provides an important basis for future breeding and production of waterlogging tolerance in alfalfa.