| Organic agriculture is a kind of agricultural production system which does not use any chemical synthetic pesticides,fertilizers and growth regulators in the production process,which emphasizes the cultivation of soil and the protection of biodiversity.A great deal of research has been done on the influence of organic agriculture on the biodiversity of farmland system,but organic agriculture advocates respecting the natural ability of plants,animals,microorganisms and landscape itself.therefore,the focus of agricultural production is to promote the natural biological cycle,make full use of the strong natural laws,regard the agricultural production system as a whole,make it as perfect as possible,and emphasize the principle of adapting measures to local conditions.It is of great significance to systematically study the important biological communities(weed community,arthropod community and soil bacterial community)by taking the organic agricultural production system as a whole.At the same time,rhizosphere soil,as the most critical area of plant growth,is the focus of nutrient transformation and soil microbial community research.Rhizosphere soil microbial community structure and soil metabolites can be understood by high-throughput sequencing and metabonomics methods.Clarify their interaction.However,the research on soil in organic agriculture is mainly focused on soil nutrients and soil microorganisms,and the research on soil metabolites and their metabolic pathways has not been carried out in organic agriculture.In this study,the weed community,arthropod community and soil microbial community in farmland ecosystem were taken as the research objects,and the unreclaimed natural habitats and conventional planting plots were compared.the differential effects of organic planting on the community structure and diversity of various groups were analyzed.On the time scale of organic planting,the effects of different organic planting years on the changes of weed,arthropod and soil bacterial community in farmland ecosystem and on biodiversity were analyzed and studied.The succession law of weed-arthropod-soil bacterial community in organic planting was explored,and combined with the changes of soil environmental factors,the driving mechanism affecting the change of biological community was clarified.With the help of non-targeted metabonomics technology,the differences of metabolites and metabolic pathways in rhizosphere soil of organic and conventional crops,the changes of microbial diversity in rhizosphere soil and the interaction mechanism with soil environmental factors were studied.The purpose of this study is to provide scientific basis for maintaining farmland ecosystem biodiversity and promoting soil health through organic agriculture.The main conclusions are as follows:(1)Long-term organic cultivation is beneficial to the improvement of weed diversity,and the species composition tends to develop in the direction of unreclaimed natural habitats.The species richness of organic planting increased,the community distribution was more uniform,and the community similarity was higher than that of wasteland,and with the increase of organic planting years,the diversity and richness of weeds showed an upward trend.Weeds in organic fields have obvious characteristics of time series change,from the community structure of Echinochloa Beauv.,Setaria P.Beauv.,Chenopodium L.and Commelina L.as the dominant species in organic cultivation for 6 years to the community structure of Echinochloa Beauv.,Chenopodium L.,Polygonum L.and Artemisia L.in 15 years.,and has the characteristics of gradual change,the community is not obvious and continuous distribution,there is a transitional community.The similarity index of adjacent communities was generally higher than that of cross-year communities,but the Whittaker index and Cody index showed a downward trend..(2)Long-term organic planting improved the community stability coefficient,which showed a trend closer to the natural habitat than conventional planting.There was no significant difference in diversity index and evenness index between wasteland and wasteland,but they were significantly higher than those of conventional planting,and on the time scale,diversity index,richness index and evenness index increased gradually.The stability index showed a dynamic upward trend,and the arthropod community in organic cultivation showed stronger ability to resist external interference and higher similarity index with wasteland.The direct control of herbivorous groups on individual number and species by natural enemies of organic cultivation and the indirect regulation of herbivorous groups by neutral groups were significantly stronger than that of conventional planting,and showed the same trend in the change.(3)Organic planting increased the diversity of soil bacterial community,and the difference of different land use patterns was mainly reflected in the community richness.The richness index of bacterial community in farmland soil was significantly higher than that in wasteland,and the soil bacterial community in organic cultivation would change with time series,and the soil with similar planting time showed a more similar bacterial community structure.The community diversity showed an increasing trend,and the richness changed in a fluctuating manner,reaching a peak in the soil with the longest organic age.Organic planting significantly increased the relative abundance of Actinobacteria and Planctomycetes,increased the trend of Actinobacteria,and significantly decreased the relative abundance of Nitrospirae.Proteobacteria and Firmicutes became the key flora in the change of organic planting flora.Proteobacteria gradually rose to the dominant group in the process of time sequence change,while the relative abundance of Firmicutes decreased obviously,losing its most dominant flora status.(4)The main driving factors of dynamic changes in different land use patterns and organic planting time series are different.In different land use patterns,soil chemical properties are important driving factors.Soil bacterial community diversity is driven by the direct action of AN and indirect action of TK,weed community diversity is driven by the direct effect of TK and indirect effect of TN,and the change of weed community diversity directly acts on arthropods,which promotes the improvement of arthropod diversity.The driving effect of weed community species number on arthropod diversity is also indirectly affected by weed community diversity.In the process of time sequence evolution of biological community,weed community and soil chemical properties are the main driving factors for the change of organic planting biological community.Soil chemical properties directly affect weed community diversity through TN,and weed community diversity affects arthropod diversity by driving richness changes.Soil chemical properties and weed communities work together to drive the evolution of soil bacterial community diversity.(5)Organic cultivation increased the diversity and richness of bacterial community in rhizosphere soil,made the relative abundance of Actinobacteria and Chloroflexi significantly higher than that of conventional cultivation,and significantly increased the richness of fungal communities in rhizosphere soil,increased the relative abundance of Ascomycota and decreased the relative abundance of Mortierellomycota.Organic planting changed the metabolic pathway of crop rhizosphere soil,changed alkaloids and other components,and affected the microbial community diversity of rhizosphere soil.There were 176 soil metabolites with significant differences between organic and conventional rhizosphere soils(p < 0.05,VIP>1).Among them,the expression of 36 metabolites increased and 140 metabolites decreased.By affecting the chemical properties of rhizosphere soil and regulating the structure of microbial community,organic planting changed the metabolites of rhizosphere soil,increased the contents of alkaloids and organic acids,and inhibited the synthesis of metabolites of benzene,hydrocarbons and organic nitrogen compounds.the metabolic pathway changes accordingly,and nitrogen metabolism and carbon metabolism become the main differential pathways.The positive cooperation between AN and Testosterone in rhizosphere soil affected the change of bacterial community diversity in rhizosphere soil.The main driving factors of rhizosphere soil fungal community diversity were metabolite L-Phenylalanine and soil chemical property ESP.To sum up,organic cultivation changed the diversity and community structure of weeds,arthropods and soil bacteria in farmland,and changed the metabolites in rhizosphere soil.The diversity of organically cultivated weed community is mainly driven by soil chemical properties of total nitrogen,total potassium and available potassium,and the diversity and richness of weed community drive the change of arthropod diversity.Soil alkalinity and weed dominance jointly drive the change of soil bacterial diversity.The main factors driving the change of soil bacterial community diversity in rhizosphere soil are soil metabolite Testosterone and available nitrogen.L-phenylalanine and alkalinity are the driving factors of fungal community diversity in rhizosphere soil. |
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