Effects Of Interactions Among Arbuscular Mycorrhizal Fungi, Rhizobia And Salt Ions On The Growth Of Medicago Sativa Under Saline-alkaline Stress

Due to climate change,agriculture,animal husbandry production,and ecological environments have been seriously influenced by global soil salinization.Salt stress generally has been the focus of numerous studies,resulting in alkaline stress being ignored,when,in fact,salinization frequently occurs with soil alkalization.The present study attempts to investigate the effects of inoculation with arbuscular mycorrhizal fungi?AMF?and rhizobia on the growth of alfalfa?Medicago sativa L.?under saline-alkaline stress?SAS?.Based on the characteristics of Chinese saline-alkaline soil and a mixed orthogonal design L₁₆?16¹×2²?,of an indoor pot experiment,alfalfa seedlings were inoculated with AMF?Funneliformis mosseae?,rhizobia,both,or neither under 16 different saline-alkaline conditions?salinity25–150 mmol/L and pH 7.67–10.52?.The conditions were created by mixing four types of salts?i.e.,NaCl,Na₂SO₄,Na₂CO₃,NaHCO₃?in various proportions.The effects of inoculation with AMF and/or rhizobia on the shoot length,aboveground biomass,underground biomass,shoot increment,activity of superoxide dismutase?SOD?,activity of peroxidase?POD?,proline content,malondialdehyde?MDA?content,soluble protein contents,root nodule number and weight of alfalfa under mixed SAS were studied.The interactions of Salt ions(Na⁺,Cl^-,HCO₃^-,CO₃^2-and SO₄^2-),AMF and rhizobia on the growth of alfalfa under mixed SAS were evaluated.We found that:1)Shoot length,shoot increment,aboveground biomass,superoxidase,peroxidase activity and protein content decreased with increasing SAS ionic concentrations and were much lower than under salt stress or alkaline stress alone.The pH of SAS was more harmful than types of soil salinization.2)shootlengthwasinfluencedbyfactorsintheorderof AMF+rhizobia>pH>AMF>SAS>rhizobia.The factors that affected shoot biomass,root biomass,high net growth of stem,malondialdehyde?MDA?and proline were ordered most to least as pH>SAS>AMF+rhizobia>AMF>rhizobia,and they affected SOD,POD,and protein orderedmosttoleastaspH>AMF+rhizobia>SAS>AMF>rhizobia,pH>AMF+rhizobia>rhizobia>AMF>SAS,and pH>SAS>rhizobia>AMF+rhizobia=AMF,respectively.The shoot length,root biomass,and POD of seedlings inoculated with rhizobia and AMF showed the maximum responses.3)Activity of peroxidase and protein content presented signigicantly positive correlection with root nodule numbers and weight respectively.MDA and proline content showed a highly significant correlation with the shoot length and the growth rate respectively.The impact of the salt ions on plants?in decreasing order?were SO₄^2--CO₃^2--HCO₃^--Cl^--Na⁺.4)There were complex interactions among salt ions,AMF and rhizobia.The strong negative correlation between Na⁺and Cl^-.Na⁺had negative correlation with HCO₃^-and Cl^-in inhibiting plant growth,while it had positive correlation with CO₃^2-and SO₄^2-.The proper concentration of salt ions could promote plant growth.5)Alfalfa's salt tolerant-ability was enhanced by inoculating with AMF and rhizobia under SAS?<75 mmol/L,pH 7.0—9.79?.AMF and rhizobia shoot length,biomass,root nodule number and weight and osmotic adjusting ability were increased in the AMF+rhizobium treatments,the combined treatment was more effective than the individual AMF and rhizobium treatments.The impact of different inoculation methods on plants were AMF+rhiozibum>AMF>rhizobium?However,the positive effects of AMF+rhizobia could not completely offset the negative effects of SAS?salt concentration 100—50 mmol/L,pH9.87—10.52?on plants.In conclusion,the interaction between salt ions was the main effect inhibiting plant growth in a certain range of concentrations.Inoculation with AMF+rhizobia could improve the resistance of plant seedlings and alleviates the damage caused by SAS.Seedlings inoculated with AMF+rhizobia could tolerate a higher concentration of salt ions.And it was more effective than inoculation with the rhizobia or AMF alone,the effect of inoculating with only rhizobia was second,and inoculating with rhizobia showed the lowest effect in the alleviating process.