Processes And Mechanisms Of Biological Regulation Of Phosphorus Cycling In Rice Fields By Periphytic Biofilm

The utilization rate of phosphorus fertilizer in China’s rice fields is low,about 10-25%in the current season,which has become one of the main limiting factors for high yield and high efficiency of rice.Therefore,it is important to study new theories and new ways to improve the efficiency of phosphorus fertilizer utilization and achieve phosphorus reduction.As an environmentally friendly phosphorus capture material,periphytic biofilm grows widely between the soil-water interface of rice fields.Periphytic biofilm in the early stage of rice growth can store large amounts of phosphorus,while periphytic biofilm in the middle and late stages of rice growth can release this phosphorus,thus changing the phosphorus supply process of rice fields.Therefore,this study aimed to investigate the potential mechanisms of phosphorus capture and release by periphytic biofilm,firstly,we constructed an indoor culture method for recovering periphytic biofilm in rice fields,and on this basis,we investigated the dynamic processes of phosphorus capture during periphytic biofilm film formation and phosphorus release during periphytic biofilm extinction,and finally,we verified the mechanisms using isotope tracing technology,and the main findings are as follows:（1）This study sorted out the dynamic process of periphytic biofilm in paddy fields throughout the rice growth period.The indoor cultivation method of periphytic biofilm in paddy field was established under the cultivation conditions of 10%of soil extract,0.5%of Woods Hole medium（WC）,and 26℃cultivation temperature,so as to realize rapid reduction cultivation of periphytic biofilm in paddy field indoors.Compared with the periphytic biofilm grown in the actual paddy field,the periphytic biofilm cultivated by this method can restore the richness of prokaryotes to 66%,and the richness of eukaryotes can reach 68%.film forming.The periphytic biofilm cultivated indoors can restore 80%of the bacterial functional species in the paddy field,and the dominant taxa in the paddy field still perform most of the metabolic functions after being cultured indoors.（2）The differences in phosphorus capture and storage mechanisms make periphytic biofilms in different periods show different phosphorus enrichment potentials.Extracellular polymeric polymers（EPS）mediate the phosphorus capture and storage process of periphytic biofilm throughout the entire rice growth period and have different contributions at different stages.From the perspective of EPS components,the ability of EPS to capture phosphorus is positively correlated with polysaccharides,proteins and extracellular deoxyribonucleic acid（DNA）in EPS.From the perspective of biological components,the dominant species throughout the rice growth period played an important role in driving the phosphorus cycle in paddy fields.Phosphorus cycling in paddy fields is mainly driven by five dominant species throughout the rice growth period.There are four main functions of periphytic biofilm affecting phosphorus cycling in different rice growth stages,and the proportions are relatively high in the whole rice growth stage.In the process of periphytic biofilm colonization and film formation,a large amount of phosphorus is captured during the attachment and growth stages of 1-16 days,and a part of phosphorus begins to be released in the form of organic phosphorus when the periphytic biofilm enters the mature stage.The calculated phosphorus flux of periphytic biofilm during the attachment and growth of periphytic biofilm was 40.296 mg P·m^-2·d^-1.The ability of the periphytic biofilm without EPS to capture phosphorus is significantly reduced at the later stage of growth.The amount of phosphorus captured by the periphytic biofilm without EPS removal is only 55%of that of the natural periphytic biofilm.The amount of phosphorus captured by the periphytic biofilm with deactivation and removal of EPS is only natural 40%,that is,the phosphorus storage of EPS is the main reason for significantly enhancing the ability of periphytic biofilm to capture phosphorus.The amount of phosphorus released by different mechanisms of periphytic biofilm is as follows:the amount of phosphorus released by periphytic biofilm during apoptosis accounted for 52%;the amount of phosphorus released by concentration difference induced 57%;the amount of phosphorus released after high temperature pyrolysis of EPS was 6%,The amount of phosphorus released by EPS accounts for 8%.The phosphorus fluxes released by different components,forms and modes of periphytic biofilm were calculated.（3）Useδ¹⁸O_P to track the whereabouts of phosphorus in periphytic biofilm,mainly explore the phosphorus used for DNA synthesis and EPS capture,and confirm the mechanism of phosphorus capture by periphytic biofilm.There is a clear gradient change ofδ¹⁸O_P with the growth of periphytic biofilm,and the growth of periphytic biofilm leads to the decrease of phosphorus in the culture system.The characteristics of these isotopes can be used as evidence that periphytic biofilm regulates phosphorus cycle.The EPS and DNA of periphytic biofilm in different growth stages were significantly different.Although the capture mechanisms are different,the two have similar capture trends.EPS plays an important role in the early phosphorus capture,which can reach up to 10 times the amount of intracellular DNA synthesis.Phosphorus held by both is released.This study reveals the dynamic relationship between functional microbial succession,functional genes and EPS dynamics and phosphorus capture process during the process of periphytic biofilm colonization and film formation,and summarizes the mechanism of phosphorus capture by periphytic biofilm;we study the dynamic relationship between apoptosis,physical structure disintegration caused by EPS degradation and phosphorus release process induced by phosphorus concentration difference in the middle and late stages of rice growth and its phosphorus release process during the extinction of periphytic biofilm,and summarize the The mechanism of phosphorus release by periphytic biofilm is summarized and verified.The present research results help to understand how periphytic biofilm affect the phosphorus cycling process in rice fields,provide a mechanism theory for artificial intervention in the phosphorus cycle in rice fields,and develop new technologies for optimizing phosphorus management and fertilization measures in rice fields based on periphytic biofilm.