Effects Of Arbuscular Mycorrhizal Fungi On Soil Phosphorus Transport And Photosynthetic Performance Of Alfalfa

Objective:In this study,alfalfa was used as the research object to investigate the effects of two fungi,Funneliformis mosseae（Fm）and Glomus etunicatum（Ge）,on the production performance and nutritional quality of alfalfa under different phosphorus application levels.In order to clarify the relationship between various growth indicators of alfalfa under the interaction of fungi and phosphorus,and the effect of fungi and phosphorus interaction on the growth of alfalfa,and to screen out the best phosphorus application suitable for high quality and high yield of alfalfa.The model was used to provide theoretical basis and practical guidance for high-quality and high-efficiency production of alfalfa.Methods:A two factor complete random design was used in the experiment.Two factors were applied:fungi and phosphorus（the phosphate fertilizer was monoammonium phosphate,containing 52%P₂O₅）.Four levels of fungi application treatment were set:single inoculation of Funneliformis mosseae（Fm,T₁）,Glomus etunicatum（Ge,T₂）,mixed strains（Fm×Ge,T₃）and non inoculation（CK,T₀）.For each fungi application treatment,four phosphorus application levels were set:P₂O₅ 0（P₀）,50（P₁）,100（P₂）and 150（P₃）mg·kg^-1.There were 16 treatments of fungi phosphorus interaction,and each treatment was repeated10 times,with a total of 160 pots.Results:（1）Under the same inoculation conditions,with the increase of phosphorus application amount,the above-biomass of alfalfa,plant height,stem thickness,growth rate,crude protein content,RFV,soluble sugar content,chlorophyll a content,chlorophyll b content,total chlorophyll content,P_n,G_s,T_r,plant leaves,stems and roots phosphorus content,p H value and alkaline phosphatase content showed a trend of first increasing and then decreasing,all reaching the highest value in P₂ treatment,and the phosphorus treatment was significantly greater than that of unapplied phosphorus treatment（P<0.05）.The contents of available phosphorus and total phosphorus increased gradually with the increase of phosphorus application,and the agronomic efficiency of phosphate fertilizer of alfalfa showed a gradual decrease with the increase of phosphorus application.（2）Under the same phosphorus treatment,the above-biomass,plant height,stem thickness,growth rate,crude protein content,RFV,soluble sugar content,chlorophyll a content,chlorophyll b content,total chlorophyll content and P_n,G_s and T_r of alfalfa treated with double fungus treatment and single fungus treatment were significantly greater than those of non-sterilization treatment（P<0.05）,and the neutral detergent fiber and acidic detergent fiber content of alfalfa showed the opposite trend of the above indicators.The phosphorus content,available phosphorus,total phosphorus content,phosphorus utilization efficiency and alkaline phosphatase activity of leaves,stems and roots of alfalfa were significantly higher than those of unsterilized treatment（P<0.05）,and the content of total phosphorus and available phosphorus reached the maximum value in T₃ treatment.The p H of alfalfa under double sterilization treatment was significantly smaller than that of unsterilized treatment（P<0.05）,and the minimum value was reached in T₃treatment.（3）A total of 7 treatments of alfalfa aboveground biomass,plant height,stem thickness,crude protein,neutral washing fiber,acidic washing fiber and soluble sugar were analyzed and evaluated,and the production indicators of alfalfa were comprehensively ranked under different phosphorus fertilization treatments,and the top three were T₃P₂>T₁P₂>T₃P₁ treatment.Pearson correlation analysis showed that intercellular CO₂ concentration（C_i）was significantly negatively correlated with dry matter yield,chlorophyll a content,chlorophyll b content,total chlorophyll content,leaf net photosynthetic rate（P_n）,transpiration rate（T_r）,stomatal conductance（G_s）and light energy use efficiency（P<0.01）,and intercellular CO₂ concentration（C_i）was significantly negatively correlated with alfalfa leaf instantaneous water use efficiency（P<0.05）.The other indexes were positively correlated（P<0.05）.Principal component analysis was carried out on 12 indexes of alfalfa dry matter yield,available phosphorus,total phosphorus,alkaline phosphatase content,p H value,alfalfa leaf,stem and root phosphorus,and the top three were T₃P₂>T₃P₃>T₃P₁ treatment.Conclusion:Under the condition of phosphorus application rate of 100 mg·kg^-1（P₂O₅）,the simultaneous inoculation of Funneliformis mosseae and Glomus etunicatum can effectively promote the absorption of available phosphorus in the soil by alfalfa plant roots and the alkaline phosphatase activity in the soil,improve phosphorus utilization efficiency and photosynthetic efficiency,then improve dry matter yield and nutritional quality of alfalfa.