Biological Effects Of FeNPs On Growth,Nitrogen Fixation And Salt Tolerance Of Alfalfa

As a common metal-based nanomaterial,nano iron(FeNPs)can change agronomic characters of crops,affect development,improve stress resistance and increase yield of plants.Medicago sativa is a perennial alfalfa in the leguminous plant with high content of crude protein,good palatability and livestock preference,which is recognized as the king of pasture in the world.Sinorhizobium meliloti(Sm1021)is a kind of Gram-negative rod-shaped bacteria,widely distributed underground,which is capable of symbiotic nitrogen fixation with legumes.In the stage of symbiotic nitrogen fixation,the iron demand of rhizobium will be greatly increased.In addition,the application of nanomaterials in salt tolerance of plants has been reported frequently,but it has been seldom used in legume forage.Exploring the biological effects of FeNPs on the growth,symbiotic nitrogen fixation and salt tolerance of alfalfa will provide a basis for the application of nanomaterials in legumes,and also provide a new idea for improving resistance and increasing yield of forage.Based on the above background,this study selected FeNPs as nano materials,alfalfa as plant material,and Sm1021 as strain material.Through hydroponics and pot experiments,the biological effects of FeNPs on growth,nitrogen fixation and salt tolerance of alfalfa were explored.The specific contents are as follows:1.10～20 mg/L of FeNPs increased the biomass,root activity and photosynthetic characteristics of alfalfa,while 100～200 mg/L of FeNPs decreased the biomass and inhibited the root activity and photosynthetic capacity of alfalfa in hydroponics experiment and pot experimen,and the optimal concentration of FeNPs for promoting the growth of alfalfa was 15 mg/L,the best application way was soak+spray.2.FeNPs can promote the growth of Sm1021,and the greater the concentration,the more obvious the promoting effect;After inoculation with Sm1021,FeNPs treatment promoted the nodulation and nitrogen fixation and growth of alfalfa,alleviated the inhibitory effect of 100 mg/L FeNPs application alone on the growth of alfalfa and improved its nutritional quality.3.Under salt stress(300 m M Na Cl),15 mg/L FeNPs increased the aboveground and root biomass of alfalfa by increasing plant height and root length;The photosynthetic capacity of alfalfa was enhanced by increasing chlorophyll content,net photosynthetic rate,transpiration rate and stomatal conductance.By increasing the root activity,the iron nutrition level was enhanced,and the iron content in plants was significantly increased.Salt tolerance was improved by reducing ROS levels,enhancing osmotic regulation and reducing Na~+ion accumulation.These results indicate that FeNPs can promote the growth,nodulation and nitrogen fixation of alfalfa,and improve its salt tolerance,which lays a foundation for the application of FeNPs in leguminous herbage,and also provides a new idea for improving the quality and yield of alfalfa.