Effects Of Straw Returning On Phosphorus Cycling Microorganisms And Key Functional Genes In Paddy Soil

Phosphorus(P)is an indispensable nutrient element for plant growth and a nutrient limiting factor in agricultural ecosystem.Its effectiveness directly determines the level of agricultural productivity.Large amounts of phosphorus fertilizer are often applied to farmland to maintain plant productivity and alleviate soil phosphorus deficiency.But most phosphate fertilizers combine with soil aggregates or sediments and convert to phosphorus that is difficult for plants to use directly.It is predicted that the phosphate ore used to produce phosphate fertilizer will run out by 2100.Straw,as an important resource to supplement soil phosphorus,can improve soil physical and chemical properties and promote microbial reproduction,thus enriching the number of active microorganisms.Microorganisms play an important role in phosphorus cycling,but how they drive phosphorus cycling under the influence of straw is not clear.Based on six years in a row of straw returned south acid paddy soil as the research object,using the soil physical and chemical testing,and optimizing the BPP classification method,macro methods of genomics and q PCR technology,research on long-term straw returned to soil available p in biological components,phosphorus cycle function gene and the influence of the microbial community composition,in order to clarify the straw in promoting the role of the phosphorus cycle.The aim is to provide scientific basis for efficient utilization of phosphorus in paddy soil,reduce resource waste and realize sustainable agricultural development.The main results are as follows:(1)Straw rewetting increased soil biologically active phosphorus fraction by increasing soil total phosphorus content.Compared with the formulated fertilizer treatment,the contents of calcium chloride-extracted phosphorus(Ca Cl2-P),citrateextracted phosphorus(Citrate-P)and enzyme-extracted phosphorus(Enzyme-P)were increased by 12.33%～19.18%,25.84%～94.38% and 6.27%～32.10%,respectively,in the paddy soils of each treatment with straw regrading.The content of biologically effective phosphorus fractions in soil for all treatments showed that HCl-P>CitrateP>Enzyme-P>Ca Cl2-P.Among them,the straw return treatment induced more organic acids secreted by soil microorganisms than phosphatase,which activated the conversion of inorganic phosphorus to Ca Cl2-P in soil.Redundancy analysis showed that soil physicochemical factors explained a high 49.15% of the variation in soil phosphorus fraction,with soil p H(F=6.6,P=0.024)and total soil phosphorus(F=4.4,P=0.038)being the key influencing factors.(2)Straw returning had a significant effect on the relative abundance of genes involved in the three processes of soil P cycling,especially on the abundance of genes involved in inorganic phosphorus activation.Redundancy analysis showed that soil organic matter(F=4.85,P=0.003),soil available phosphorus(F=4.74,P=0.007)and alkaline phosphatase activity(F=2.87,P=0.041)were significantly correlated with soil phosphorus cycling gene abundance,respectively.(3)Straw returning significantly changed the community composition of soil phosphorus solubilizing bacteria,increased the bacterial richness,and increased the relative abundance of Bradyrhizobium containing pqq C gene and Bellilinea containing ppx gene,thus enhancing the phosphorus solubilizing ability of soil microorganisms.Redundancy analysis showed that soil physical and chemical factors accounted for more than 70% of the bacterial community variation in key genes of phosphorus cycle,in which phosphatase mainly regulated the bacterial community changes containing pqq C and pho D genes,and p H mainly regulated the bacterial community changes containing ppx genes,thus affecting the mutual transformation of different phosphorus components.(4)Straw returning can stimulate the abundance of bacterial community containing pho D and pqq C genes by increasing the relative abundance of pho D and pqq C genes,and enhance the availability of soil phosphorus,especially the active inorganic phosphorus(Citrate-P)and active organic phosphorus(Enzyme P).However,ppx gene and the bacterial community containing ppx gene showed the activity of soil p inhibition.In conclusion,straw returning can increase the abundance of pqq E,pho-(ABD)and glp-(ABCDFKOQR)genes,Chloroflexi and Verrucomicrobia by changing soil p H,available potassium and total phosphorus.Thus,it can promote the activation of soil accumulated phosphorus,improve the content of soil Citrate-P and Enzyme-P.