| Efficient utilization of phosphorus and effective absorption and utilization of phosphorus nutrition in soil play an important role and significance in the growth and yield of alfalfa.In order to study the growth of alfalfa,soil enzyme activities and metabolic function diversity of rhizosphere microorganisms under different phosphorus supply levels,this study selected"Xinmu No.1"as the research object.Field experiments were conducted to study the growth characteristics,differences of phosphorus absorption and utilization,changes of soil enzyme activities and metabolic function diversity of rhizosphere microorganisms of alfalfa under different phosphorus gradients:0kg/hm~2(P0),75kg/hm~2(P1),150kg/hm~2(P2),300 kg/hm~2(P3)and450 kg/hm~2(P4).The regulation law of phosphate fertilizer concentration on alfalfa growth,soil enzyme activity and functional diversity of rhizosphere microorganisms was mastered.The influence mechanism of phosphate fertilizer on alfalfa growth,utilization rate of phosphate fertilizer and rhizosphere microorganisms was revealed,and the optimum amount of phosphate fertilizer applied to increase alfalfa yield was determined,so as to provide theoretical basis for alfalfa industry.The main results include:(1)Effects of different phosphorus supply levels on growth characteristics of alfalfa:The results showed that with the increase of phosphorus fertilizer concentration,the aboveground and underground biomass,root-shoot ratio and seed yield of alfalfa generally increased at first and then decreased.Under P2treatment,biomass,root-shoot ratio and seed yield reached the maximum.The total phosphorus content of alfalfa roots increased first and then decreased,and the total phosphorus content of alfalfa roots reached the maximum value at P2.At the same level of phosphate fertilizer,the total phosphorus content of alfalfa roots reached the maximum at full flowering stage.(2)Characteristics of changes of soil enzyme activities under different phosphorus supply levels:soil alkaline phosphatase activity gradually increased with the increase of phosphorus level,catalase activity gradually decreased with the increase of phosphorus level,and soil urease activity generally showed a trend of increasing.Through correlation analysis of alfalfa growth index and soil enzyme activity,it was found that there was a high correlation between catalase activity and alfalfa biomass,and urease activity had a high correlation with total phosphorus content in roots.(3)Effects of different phosphorus supply levels on functional diversity of alfalfa rhizosphere microorganisms:Applying phosphorus fertilizer can effectively increase the metabolic activity of alfalfa rhizosphere microbial communities,improve the utilization rate of different carbon sources by alfalfa rhizosphere microorganisms,and significantly increase the metabolic diversity index of microbial communities.However,if the concentration of phosphate fertilizer is too high,it will inhibit the growth and metabolism of microbial communities,thus reducing the metabolic activity of microorganisms,the dominance index of microbial communities and the utilization rate of various carbon sources.In conclusion,the growth characteristics of alfalfa varied significantly under different phosphorus fertilizer levels,and its root uptake and utilization of phosphorus fertilizer also varied according to phosphorus concentration.The response mechanisms of soil enzyme activity and rhizosphere microbial functional diversity to phosphorus fertilizer concentration also differed,and moderate phosphorus fertilization could increase alfalfa yield and phosphorus uptake and utilization,and rhizosphere microbial activity,while excessive phosphorus concentration inhibited the conversion and uptake of phosphorus fertilizer by the rhizosphere microzone. |
