Effects Of Phosphorus Application On Microbial Community Structure In The Rhizosphere Of Mustard-maize In Purple Soil

Soil rhizosphere microbes participate in soil phosphorus（P）cycling directly or indirectly,thereby affecting plant nutrient uptake and soil health.In recent years,excessive P fertilizer application has caused a large amount of P accumulation in soil,which has become a potential source of agricultural non-point source pollution.Optimizing P fertilizer application and fully exploiting the biological potential of rhizosphere microbes is an important way to reduce the input of phosphate fertilizer and improve the utilization efficiency of phosphate fertilizer,which can ensure the crop yield and realize the sustainable development of green agriculture.In this study,the mustard-maize rotation system was used to explore the effect of P application on the rhizosphere microbial community structure of purple soil sloping farmland.The experiment was set up with two P application treatments:conventional P application(125 kg P₂O₅ ha^-1,P125)and optimized P application(90 kg P₂O₅ ha^-1,P90).Based on the analysis of the rhizosphere microbial community diversity and structure of the rotation system during the whole growth period,the maize rhizosphere microbes and phosphate-solubilizing genes（pho D and pqq C）of the community structure change characteristics were systematically studied.These results will provide theoretical evidence for understanding the biological potential of rhizosphere microorganisms in P cycling and improving P utilization efficiency.The main results of this study are as follows:1.The OTUs（operational taxonomic unit）of the rhizosphere bacterial community of both mustard and maize were higher than that of the fungal community,which indicated that the richness of bacterial community was greater than fungal community.Actinobacteriota and Ascomycota were the dominant phyla shared by mustard and maize rhizosphere,and Olpidiomycota is the unique fungal taxa in mustard rhizosphere.The effect of different P application levels on the microbial community composition of maize rhizosphere was significantly greater than that of mustard.2.Affected by different P application levels,the diversity and richness of maize rhizosphere bacterial communities showed dynamic changes in four growth stages（seedling stage,ear stage,flowering stage and harvest stage）,while no significant change was observed in fungal communities.The composition of rhizosphere microbial community structure was strongly influenced by P application levels and growth stages.In the bacterial communities,Actinobacteriota and Proteobacteria were the dominant bacterial phyla in the rhizosphere of maize at each growth stage.Compared with P125,P90 significantly increased the relative abundance of microbial taxa such as Chloroflexi,Bacteroidota,Mycobacterium,Actinospica and Acidothermus.In the fungal communities,Ascomycota and Basidiomycota were the dominant taxa.P90 significantly increased the relative abundance of Talaromyces（ear stage）and Glomeromycota（flowering stage）,and decreased the relative abundance of Fusaium and Cladophiaiophora at harvest stage.These results suggest that maize would recruit unique microbial taxa at different growth stages in response to differennt P application levels.In addition,soil total nitrogen（TN）and p H were the main drivers of changes in bacterial and fungal community structure,respectively.The network analysis indicated that the differences of key taxa in two P fertilization treatments might affect the complexity and adaptability of the microbial interaction network directly or indirectly.3.P application levels and growth periods significantly affected the abundances of pho D and pqq C,as well as community diversity.P90 significantly increased the pho D abundance at ear and flowering stages,while decreased the pqq C abundance during the whole growth stage.Proteobacteria and Novosphingobium were the dominant taxa in pho D-and pqq C-harboring bacterial communities.P application differences had greater effects on pho D-and pqq C-harboring bacterial community structure than growth periods.P90 significantly increased the relative abundance of Pseudomonas and Brevundimonas at the flowering stage.Available nitrogen（AN）and ammonium nitrogen（NH₄-N）were the first environmental drivers of changes in pho D-and pqq C-harboring bacterial community structure,respectively.Under P90,Pseudomonas was the key taxa in the microbial interaction network of pho D-and pqq C-harboring bacterial community,which could lead to higher complexity and adaptability of their community structure.In conclusion,the effect of P application difference on maize community structure was greater than that of mustard.Different P application levels and growth stages significantly affected the structural composition of maize rhizosphere bacterial,fungal communities and pho D-and pqq C-harboring bacterial community.Under the optimized P application,maize rhizosphere recruited some beneficial microorganisms at specific growth stages,which could improve the resistance of their community structure to changes in the external environment,thereby helping to alleviate P deficiency.