Physiological Responses Of Leymus Chinensis Arbuscular Mycorrhizal Symbionts To Salt And Drought Cross Stress

Leymus chinensis is a high quality forage grass,which not only has rich nutritive values,but also has strong resistance to adversity.It is a constructive species in Northeast salt-alkali grassland of China,and also a good grass species for artificial grassland construction Arbuscular mycorrhizal fungi(AMF)is a kind of soil microorganism,which can symbiotic with more than 80%of terrestrial plants and is widely distributed.It plays an important role in regulating plant growth and resistance.Based on this,this paper takes L.chinensis-arbuscular mycorrhizal symbiont as the object,and carries out the saline alkaline-drought cross stress,in order to reveal the physiological response of L.chinensis arbuscular mycorrhizal symbiont.(1)With the increasing salinity and drought stressees,the colonization of AMF decreased significantly(P<0.05),and much stronger under alkali stress.Under the effect of cross stress,the infection rate of AMF was also decreased,and the effect of alkali-drought cross stress was more obvious.The colonization of AMF was only 46.6%when alkalinity was 200 mmol/L and PEG concentration was 10%.(2)In single type stress,the fresh weight and dry weight of L.chinensis seedlings were significantly increased compared with those without AMF inoculation(P<0.05).In the cross stress treatment group,the growth of L.chinensis seedlings was inhibited,and the fresh weight and dry weight decreased with the increasing stress.However,the fresh weight and dry weight of L.chinensis seedlings showed an increasing trend in the cross stress treatment at low salt concentration(100 mmol/L)and 5%of PEG concentration.The results showed that lower concentration of salt and drought stress did not inhibit the growth of L.chinensis seedlings,but showed a cross adaptability between salt and drought stress.Under the cross stress,the AMF treatment also alleviated the damage of L.chinensis seedlings under the stress of AMF treatment.(3)With the increasing salinity,the Na+,Ca2+,Mg2+,and Cl-contents in L.chinensis seedlings were increased significantly,while the K+ and NO3-contents decreased significantly(P?0.05).Under alkali stress,with the increasing alkalinity,the Na+ and Cl-contents were increased,and the Ca2+ and Mg2+contents were decreased in a small amplitude,while the K+and NO3+ contents were decreased significantly(P?0.05).Under drought stress,there was no significant change in ion content.After AMF inoculation,the K+ content of L.chinensis seedlings were increased,the Na+and Cl-contents were decreased,and the NO3" content increased,indicating that inoculation of AMF can inhibit the absorption of Na+and Cl-in the seedlings of L.chinensis,thus reduce the toxic effect of Na+,enhance the absorption of K+,and keep the ion balance with in the cells,thus alleviating the damage of salt and alkali stress to the seedlings.The same conclusion is reached for the analysis of cross stress.In addition,under salt stress,low concentration of drought stress did not aggravate the absorption of Na+.However,under alkali stress,alkali-drought cross stress increased the Na+content,indicating that alkali-drought stress had a greater impact on the plant arbuscular mycorrhizal symbiosis,and arbuscular mycorrhiza had a certain effect of slow stress injury.(4)The proline content of L.chinensisseedlings increased with the increasiing stress concentration.The increases of proline content in mycorrhizal symbiont after AMF inoculation increased the osmoregulation and played a positive role in regulating the stress resistance of L.chinensis seedlings.In the cross stress treatments,the damage effects of L.chinensis seedlings were higher than that of single stress,and the accumulation of proline was increased.(5)Salt or alkali stress had little effect on the change of organic acid content in L.chinensis seedlings.However,under alkali stress,the organic acids contents of each treatment increased to varying degrees.After inoculation with AMF,the content of organic acids decreased.Under the cross stress,malic acid and citric acid increased with the incredsing cross stress,regardless of whether or not it was followed by the AMF treatment,and the increase was slowed down by the inoculation of AMF.(6)Under the single stress,with the increasing of stress concentration,the MDA content was increased,and the activities of SOD,POD,CAT and APX also increased significantly(P<0.05).After AMF inoculation,the MDA content in the L.chinensis seedlings decreased and the activity of POD,CAT but APX increased obviously.It showed that the mycorrhizal symbiosis relieved the peroxidation of membrane and enhanced the scavenging ability of oxygen free radicals in the host plant.Compared with the control,the activity of SOD,POD and APX decreased,and the activity of enzyme increased after inoculation with AMF,which reduced the damage effect of free radicals to the cells.However,the activity of CAT increased in the cross treatment that was not inoculated with AMF,which may be a kind of adaptation mechanism under the cross stress,so the activity of CAT was changed.