The Response Mechanism Of Soil Phosphorus Solubilizing Microorganisms To Cirtus Planting Years And Exogenous Phosphorus Addtion

Phosphorus(P)is one of the most important macronutrients for all biota.However,in agricultural soils,phosphorus will be fixed by soil solid phase components or lost with runoff easily.The proportion of phosphorus which can be directly utilized by plants and microorganisms was relatively low,therefore P had been considered as a major factor regulating the primary productivity in terrestrial ecosystems.In order to alleviate phosphorus limitation in soil,a large amount of phosphate fertilizer was applied,but it would cause the decline of soil quality and biodiversity,especially in the highly intensive citrus system.Activating soil organic phosphorus and increasing the supply of soil phosphorus are the foundation for the development of sustainable agriculture.Soil phosphorus-solubilizing microorganisms are the main driving force of the soil phosphorus cycle,they can produce organic acids and phosphatase to convert organic phosphorus into inorganic phosphorus,which can be directly used by plants.Therefore,this study aimed to study the phosphorus status in the soil with different citrus plantation years and the response of phosphorus-solubilizing microorganisms to exogenous external phosphorus addition,and to clarify the main environmental factors that affect the composition and structure of phosphorus-solubilizing microorganisms.These results would be helpful to understand the turnover of phosphate fertilizer in soil,and to improve the utilization rate of phosphate fertilizer and relieve phosphorus limitation for soil microbial communities.We sampled the citrus soil with different plantation years in Zigui County,which was located in Three Gorges Reservoir area,we used enzymatic vector model analysis to evaluate the phosphorus limitation for microbial communities in soil under different plantation ages.A mesocosm experiment was conducted to study the effects of the P addition on microbial community structure and composition of phosphorus-solubilizing microorganisms via high-throughput sequencing,and the abundance of phoD and phoC genes via q PCR.We also studied the key factors in shaping the community structure of soil phosphorus-solubilizing microorganisms.The main results were listed as follows:(1)With the increase of plantation years,citrus soil p H decreased from 7.4 to 3.5,and the contents of total phosphorus(TP)and Olsen-P increased to 1.43 g/kg and 188.2mg/kg;the abundance of phoD and phoC genes significantly decreased,and the angle of the enzymatic vector gradually increased(>45°).These results indicated that the long-term intensive citrus plantation would lead to soil acidification and phosphorus accumulation,and relatively P limitation for soil microbial communities and this 2021limitation became more serious along with increasing plantation ages.(2)In microcosm experiments,for no addition of exogenous phosphorus treatments,the angle of enzymatic vector in natural forest soil and 5-year citrus soil decreased,but it was still higher than 45°.However,under high phosphorus addition,the enzymatic vector angle decreased.The angle became larger in 10-year citrus soil regardless of the concentration of exogenous phosphorus added.This showed that in the soil with low phosphorus stocks,appropriate application of phosphorus fertilizer will reduce the microbial phosphorus limitation,but the high input of phosphorus will strengthen the microbial phosphorus limitation.In the long-term intensive citrus plantation,the higher phosphorus accumulation and continuous P fertilizer application,led to a stronger phosphorus restriction.Therefore,appropriate increase in organic fertilizer should enhance the activity of soil microorganisms and alleviate nutrient limitations.(3)With the increase of plantation years,the dominant bacteria phyla encoding phoD genes gradually transitioned from Proteobacteria-dominant(12.68 %?57.37 %)to Actinobacteria-dominant communities(5.30 %?61.86 %).The dominant genera shift from change from Phaeobacter to Streptomyces and Amycolatopsis indicated that the long-term intensive citrus plantation significantly changed the composition of the microbial community encoding phoD gene,The high P improved the correlation between the abundance of the phoD gene and environmental factors,and the relative abundance of Streptomyces(phosphorus-solubilizing microorganisms).We inferred that high P fertilizer inputs to soil,would activate phosphorus-solubilizing microorganisms instantaneously,but this positive effect will be weak in the long term.(4)Correlation analysis and redundancy analysis(RDA)showed that soil TP is the most important environmental factor affecting the community composition and structure of phosphorus-solubilizing microorganisms.In addition,other environmental factors such as soil p H also have a significant impact on phosphorus-solubilizing microorganisms.For highly intensive citrus plantation,we suggested that we could reduce the inputs of chemical P fertilizer and increase the application of microbial organic fertilizer to enhance the activity of soil phosphorus-solubilizing microorganisms and promote the expression of phoD,phoC and other functional genes,which controlled the process of inorganic phosphorus dissolution and organic phosphorus mineralization,thereby increasing the effectiveness of phosphate fertilizers.