Response Of Soil Microbial Communities And Metabolites To Phosphorus Fertilizer Management In Dryland Farmland

Phosphorus（P）,one of the important factors limiting crop growth and development,plays an important role in maintaining soil fertility and improving the sustainability of agricultural production system.However,soil P in farmland has the characteristics of low availability and poor mobility,and the vast majority of phosphorus exists in the form of unabsorbable and unavailable by crops,which lead to less than 1%of P can be absorbed and utilized by plants.Therefore,increasing the content of available P in soil is still a key problem to be solved in current and future agricultural production.Soil microorganisms directly participate in the P-cycle and play a key role in the dissolution of soil inorganic P and the mineralization of organic P.Therefore,fully tapping the biological potential of soil microorganisms is an important way to improve soil available P.This study relied on the Changwu Agricultural Ecology Experimental Station of the Chinese Academy of Sciences,and took winter wheat farmland as the research object,Hedley P fractionation,high-throughput sequencing and non-target metabolomics were used to study the characteristics of soil microorganisms and metabolism treated by different phosphorus application levels(0,60 and 120 kg P₂O₅ ha^-1)and application modes（strip and broadcast）.The interaction mechanism among soil biochemical properties,P availability and microbial community structure was investigated,which helps to provide important scientific basis and data support for improving soil P availability in dryland farmland and green sustainable development of agriculture.The main results were showed as follows:（1）Based on different phosphorus fertilizer management levels,the biochemical properties of soil farmland at different growth stages of winter wheat and the content of soil P fractions at maturity were analyzed,P application levels and modes affected soil available nutrients and enzyme activities to varying degrees,especially significantly increased soil available P content of different soil layers in different growth periods of winter wheat,and reached the maximum in the filling stage,among which,the content of available P in 0-20 cm soil reached 22.87 mg kg^-1 at the filling stage of winter wheat under broadcast 120 kg P₂O₅ha^-1 treatment in 2019,and there was significant difference between the treatments with and without P application（P<0.05）,and the content of available P in 0-20 cm soil was higher in the broadcast application than in the strip application.Further analysis of different P fractions based on Hedley fractionation method showed that P application levels and modes can significantly change the levels of soil P fractions,among which,high-P treatment(120 kg P₂O₅ha^-1)significantly increased the contents of soil organic P（Na HCO₃-Po,Na OH-Po and HCl _C-Po）and inorganic P（Na HCO₃-Pi,Na OH-Pi and HCl _C-Pi）both under strip and broadcast application.（2）The soil microbial diversity,community structure and symbiotic network of winter wheat under different P fertilizer management were studied through high-throughput sequencing.The results showed that applying P fertilizer significantly changed soil bacterial and fungal diversity and community composition structures and the interaction between microorganisms.The application of P fertilizer reduced the complexity of microbial community network in 0-20 cm soil layer,but enhanced the interaction between soil microorganisms,in addition,P application modes significantly caused the changes of key species in microbial networks.Further,through redundancy analysis（RDA）and structural equation model（SEM）,it was found that the main environmental factors driving the change of microbial community under P application were total P and available P.More importantly,it was found that Different P application levels and modes significantly caused the changes in the relative abundances of functional genes of soil bacteria and fungi through functional prediction.（3）The response of soil metabolic characteristics of winter wheat to different P application levels and modes was studied by ultra-high performance liquid chromatography tandem mass spectrometry（UHPLC-MS/MS）.The study found that a total of 582 metabolites were detected in soil under P fertilizer management,and 14 important differential metabolites proved important compounds involved in plant growth and development were selected under P fertilizer management through the enrichment analysis of differential metabolites,among which Trigonelline,Normorphine,Morphine and Piperine were alkaloids and their derivatives,Trigonelline,L-Glutamic acid,L-Isoleucine and N-Acetylcholine were organic acids and their derivatives,6-Hydroxynicotinic acid,Indole-3-acetic acid and Nicotinic acid were organic heterocyclic compounds,and these differential metabolites played an important role in glycolysis,pentose phosphate pathway,amino acid metabolism and P cycle.Further analysis of the 14 differential metabolites found that the relative contents of Trigonelline,Phosphocreatine,Shikimic acid,L-Glutamic acid and Diosgenin were significantly increased after broadcast application at 60 kg P₂O₅ha^-1.Based on Spearson correlation analysis,it was found that there was significant correlation between soil dominant microorganisms and differential metabolites,which suggested that these microorganisms may participate in the absorption and transformation of soil nutrients through a series of metabolic pathways.Therefore,different P application levels and modes can change soil P fraction,chemical properties and enzyme activity levels,and change the transformation process of P nutrients by affecting soil microorganisms and metabolites,which can provide a scientific basis for the scientific P fertilizer management in wheat farmland in the Loess Plateau.