| The selection of phosphorus-efficient alfalfa varieties is very important for alfalfa to effectively absorb phosphorus nutrients from the soil.In order to explore the different varieties of alfalfa in 0（P0）,50（P1）,100（P2）,500（P3）),1000（P4）and 1500（P5）（?）mol/L（Hoagland nutrient solution with KH2PO4 as the phosphorus source）the response difference of root system and physiological characteristics under 6phosphorus levels.In this study,alfalfa varieties with different phosphorus efficiency,Xinmu No.1,Magnum salt,Longdong,Longmu 801,Zhaodong,and Magnum II were selected.Through the nutrient solution hydroponic test method,six varieties were tested under the phosphorus level.Research on the characteristics of alfalfa root system,differences in phosphorus nutrition and differences in root acid phosphatase activity,and analyzed 6 varieties of purple flowers tested under normal phosphorus levels（500（?）mol/L）and low phosphorus levels（50（?）mol/L）variation degree,correlation and low phosphorus tolerance of 16 traits of alfalfa.On this basis,three representative varieties of alfalfa were selected,namely,the high-efficiency Magnum salt,the medium-efficiency Longdong,and the low-efficiency Zhaodong.The effects of inoculation of Chinese rhizobium on different phosphorus efficiencies under six phosphorus levels were further studied.The effects of alfalfa photosynthetic characteristics,plant growth,nutrient utilization and nodule characteristics.The main findings include:（1）Root system characteristics of six alfalfa species under different phosphorus levels:the total root length and root surface area of alfalfa reached the maximum under low phosphorus environment.Excessive phosphorus concentration would inhibit the growth of alfalfa underground and reduce the total root length and root surface area.The total root length and root surface area of Longdong and Longmu 801 were smaller than the other 4 varieties at the P2 low phosphorus level.The root acid phosphatase activity of the 6 varieties all reached the maximum under the P1 low-phosphorus treatment,and the root acid phosphatase activity of the Magnum salt and Juneng II was significantly higher than the other 4 varieties under the low-phosphorus treatment.Comprehensive indicators of total root length,root surface area,root phosphorus absorption efficiency,and root acid phosphatase activity indicate that Xinmu No.1 and Magnum salt have higher phosphorus tolerance than other varieties and are better varieties with high phosphorus efficiency.（2）Nutrient accumulation characteristics of six alfalfa species at different levels of phosphorus supply:with the increase of phosphorus supply levels,the plant height,dry matter accumulation,plant nitrogen accumulation,and plant potassium accumulation of the six alfalfa all showed a slow increase first and then the tendency of gradual decrease,and all treatments with phosphorus supply are greater than those without phosphorus supply.Excessive or too low phosphorus concentration will inhibit plant growth.P3 treatment is more conducive to plant growth and dry matter accumulation.The accumulation of phosphorus in plants of various products with the increase of the phosphorus supply level,the phosphorus supply treatments were significantly higher than those without phosphorus supply.The phosphorus use efficiency of plants was significantly negatively correlated with the phosphorus content,and the phosphorus use efficiency at low phosphorus levels was significantly higher than that at medium and high phosphorus levels.There are differences in the phosphorus use efficiency of various plants at the same phosphorus level.Comparing the comprehensive physiological indexes and the characteristics of phosphorus nutrition,it is found that Xinmu No.1,Magnum salt,Longdong 801,Zhaodong and Magnum II have stronger low phosphorus tolerance.（3）Correlation analysis of various traits of alfalfa under normal phosphorus and low phosphorus levels:under two phosphorus supply conditions,analysis of coefficient of variation,correlation analysis,principal component analysis and low tolerance of 16 traits of six varieties of alfalfa.The analysis and comparison of the phosphorus coefficient found that there were differences in the degree of variation of the variety index and the correlation between the traits under the two phosphorus levels.A comprehensive comparison of physiological indexes and phosphorus nutrition characteristics found that the Magnum salt had the highest phosphorus efficiency among the 6 varieties,which belonged to phosphorus high-efficiency varieties,followed by Xinmu No.1 and Longdong,Longmu 801.Zhaodong and Magnum II belong to the varieties with lower phosphorus efficiency.（4）The effect of phosphorus level and rhizobia inoculation on the growth of three kinds of alfalfa with different phosphorus efficiency:after rhizobia inoculation,under 6 phosphorus supply levels,the phosphorus-efficient variety of Magnum salt underground biomass,aboveground biomass,plant dry matter accumulation,plant height,plant phosphorus accumulation,number of nodules per plant,and nodule weight were higher than those of Longdong,a medium-efficiency variety of phosphorus and Zhaodong,a low-efficiency variety of phosphorus.The stomatal conductance and net photosynthetic rate of the three varieties of alfalfa leaves as the phosphorus concentration increases,it first increases and then decreases,and both reach the peak when the phosphorus concentration is 1000（?）mol/L.The transpiration rate and intercellular CO2 concentration generally decrease with the increase of phosphorus level,and show as the photosynthetic capacity of the Magnum salt cultivar with high phosphorus efficiency is stronger than that of the cultivars with medium phosphorus efficiency and low phosphorus efficiency.Appropriately increasing the phosphorus concentration after inoculation with rhizobia can promote the growth of alfalfa,and the P4 treatment after inoculation with rhizobia is more beneficial to alfalfa plant growth.In summary,the root system and physiological characteristics of different alfalfa varieties have adaptability and differences under different phosphorus treatments,and the root system and physiological response mechanism of phosphorus efficiency of alfalfa under different phosphorus treatments are also different.Phosphorus deficiency and excess phosphorus will affect the root system and physiological characteristics of alfalfa.Compared with low phosphorus efficiency,alfalfa varieties with high phosphorus efficiency can better adapt to low phosphorus stress in the growth environment. |
