Study On The Effects Of Reduced Fertilizer Incorporated With Organic Matter On The Leaching And Transformation Of Carbon,Nitrogen,Phosphorus And Variations Of Soil Microbial Community Structure In Paddy Wetland

This study aims to the migration and transformation of carbon,nitrogen and phosphorus in paddy wetland water and soil during the process of prevention and control of agricultural nonpoint source pollution.From the perspectives of source optimized fertilization,field localization and leaching simulation trial were conducted to study leaching law of paddy field water and soil carbon,nitrogen and phosphorus,greenhouse gas emission characteristics,changes of microbial community structure,source identification of dissolved organic matter fluorescent components and their influence factor under the condition of reduced fertilizer incorporated with organic matter?Wheat straw:WS,Raped shell:RS,Astragalus smicus:AS?,which coupled with the technologies of soil soluble collection equipment,high-throughput sequencing and excitation-emission matrix parallel factor model.Results obtained in this study were used to hunt for the controlling measures of nonpoint source pollution,explore paddy soil GHG emission and its microbial mechanism,reveal the variation of soil DOM and its source analysis,provide theoretical support and scientific basis for energy conservation and efficiency in paddy field.The main conclusions gained in the present study were summarized as following:?1?Concentrations of surface water total nitrogen?TN?,total phosphorus?TP?were peak after fertilization 1 day,and keep stable basically during the of late growth period of rice.Average contents of TN and TP decrease by 94.1%,99.6%,respectively after rice transplanting 57 days.The loss of TP in runoff was dominated by particle phosphorus?PP?,whose leaching amount was the 4.5 times of dissolved phosphorus?DP?.The runoff loss amount of TP was significantly higher than accumulated leaching amount?p<0.05?,which was mainly influenced by rainfall and other environmental factors.Of all fertilization practices,reduced fertilizer incorporated with AS can control the losses of paddy field nitrogen and phosphorus effectively,and the polluting effect of reduced fertilizer incorporated with WS?RFWS?reduced fertilizer incorporated with RS?RFRS?should be considered in the process of rice production.?2?WS,RS and AS amendments significantly increased the contents of topsoil?0-10cm?TN,TP and available phosphorus?AP??p<0.05?.The leaching amount of dissolved organic carbon?DOC?decreased with the increase of soil depth in the period of leaching.The mean concentration of DOC increased in the later stage of leaching,which resulting from the DOC release of WS,RS and AS,gradually.The average concentrations of surface water TN and TP showed a declining trend,which decreasing by 75.8%and 96.6%,respectively,at the end of leaching.The leaching events of TN and TP mainly occurred in0-20 cm soil layer,which accounting for the 71.8%and 63.3%of total leaching amount,respectively.The results obtained in leaching test showed that the fertilization measures of RFWS?RFRS and RFAS accelerated the leaching losses of N and P under the ideal conditions without rainfall and rice planting.?3?The fertilization measures of RFWS?RFRS and RFAS promoted soil CH₄ and CO₂emission,whereas decreased the accumulative emission amount of N₂O with 25.9-73.7%relatively to conventional fertilizer?CF?.The abundance and diversity of soil bacterial communities were significant enhanced with the addition of exogenous organic matter,and Proteobacteria was regarded as the most dominant one.The community structure between RFWS?RFRS and RFAS displayed a high similarity,while posting a significant difference comparing with control?CK?and reduced fertilizer?RF?.?4?The DOM content of soil after leaching ranged from 0.05 to 0.14 g kg^-1,decreasing with the increase of soil depth.Organic matter amendments can also increase the soil DOM fluorescent intensity and the contents of fluorescent components markedly.The mean values of specific adsorption at 254 nm(SUVA₂₅₄)and slope ratio?S_R?indicated that the high aromaticity and molecular weight of DOM.Six fluorescent components were identified by EEM-PARAFAC,including UVC humic-acid like component?C1?,UVA humic-acid like component?C2?,soluble microbial metabolites like component?C3?,aromatic or proteins like component?C4?,fluvic-acid like component?C5?,aromatic or proteins like component?C6?,and C1,C2 were the main materials with a total distribution 56.6%.?5?Reduced fertilizer incorporated with wheat straw biochar pyrolysis at 300,500 and700??RFBC300,RFBC500,RFBC700?significantly increased the accumulative emission of CH₄ and CO₂?p<0.05?,however,BC300 showed a better inhibitory effect for N₂O emission flux.The correlation between surface water DOC concentration and CH₄ emission flux was positive.The abundances of 0-10 cm soil archaeal and bacterial communities increased with abundances of Methanomicrobia 44.6-56.2%,Alphaproteobacteria17.1-20.6%,which were related to the production and emission of CH₄.However,the net CH₄ emission flux was regulated by the variation of the methanogens to methanotrophs ratio.?6?DOM released by BC300,BC500 and BC700 ranged from 0.61-1.45 g kg^-1,meanwhile,biochar DOM aromatic compounds and molecular decreased with the increase of pyrolysis temperature.EEM-PARAFAC fluorescent components mainly contained proteins or tryptophan like material?C1?,UVA humic-acid material?C2?and UVA humic-acid like material?C3?,which originated from terrestrial or organic matter source probably.The distributions of C1 and C2 decreased,while C3 increased with pyrolysis temperature increasing.