Effects Of Species And Quantity Of Cover Crop On Soil Nematode Community Based On Functional Trait Approach

Reducing the input of agricultural chemicals and increasing the input of organic matter can promote the development of soil biological community and improve the multi-functional service of soil.Therefore,measures of weight loss and organic matter input are the core countermeasures for the development of ecological agriculture.Based on abundant evidence from natural ecosystems,the quality(species or chemical composition)and quantity of organic matter supported by different plant species are key traits that support the structure and function of the soil food web,and determine key ecological processes such as energy flow,nutrient transformation and organic carbon accumulation in soil ecosystems.So far,it is still in its infancy to use the concept of plant functional traits to regulate the structure and function of the soil food web in agricultural soil ecosystems.Based on plant functional traits,we can better understand the rules of the influence of different cover crop groups on the structure and function of the soil food web,which not only helps to reveal the regulation mechanism of cover crop on the function of farmland ecosystem,but also is an important prerequisite for rational utilization and management of cover crop resources.Soil nematode is abundant in quantity,species and life history,and it has a unique advantage in reflecting the changes of structure and function of soil food web under the effect of different plant functional traits.In view of this,this study used nematode community to analyze the structure of the food web in the indicative soil,and explored the influence and mechanism of the cover crop groups based on the classification of plant functional traits on the soil nematode community.In this study,the relationship between the functional traits of cover crop and the soil nematode community in the growth and decomposition stages was systematically discussed based on the dynamic analysis of the plant-decomposition process of cover crop.The first part of the study was a field plot experiment in which 18 species of cover crop were planted.The main crops were sampled in the cover crop growth period,the early and late decomposition period to explore the influence of cover crop on the community structure of nematode.The second part of this study was a field micro-decomposition tube test which was set up based on the former results.The experiment was 3 levels complete interactive design with 2 factors(cover crop species and the amount of incorporation),in which the cover crop include leguminous turpentine(Astragalus sinicus L),cruciferous rapeseed(Brassica campestris L.)and gramineous ryegrass(Lolium multiflorum Lam.),and the amount of returning rate was respectively set at 0,2500kg ha-1,5000kg ha-1.Decomposition of cover crop residues was carried out in the field using decomposition tubes and samples were taken at the 26th and 138th days after the residue was returned.The research goal of this part was to explore the interaction effects of typical cover crop species and the amount of residue returning on the nematode community structure.The main results of first experiment showed that:1)Based on plant functional traits(lignin content,biomass,etc.),cover crop was divided into four groups:gramineae,cruciferae,leguminosae 1 and leguminosae 2 groups;It was found that the functional traits of cover crop plants,such as the aboveground carbon to nitrogen ratio lignin content,root biomass and root nitrogen content,significantly affected the number and community structure of soil nematode worms and the energy passage of soil food web.2)In the early and late decomposition stages,the legacy effect of cover crop mainly affected the number and community structure of soil nematode and the energy passage of soil food web through underground functional traits such as root biomass and root nitrogen content.3)During the crop growth period,maize biomass significantly affected the structure of nematode community,as well as the rhizosphere and fungal energy channels.4)With the process from the cover crop growth period,the incorporation and crop growth period,the energy channels of the soil food web gradually turned from the bacteria energy channels to the rhizosphere energy channels,especially gramineae cover crop group.The main results of the second experiment showed that:1)in the two samples of cover crop residues at the early stage of decomposition(decomposition 26d)and at the later stage(decomposition 138d),the interaction between the cover crop species and the incorporation affected the number and biomass of nematode and the community structure by reducing the soil pH and increasing the content of Dissolved organic carbon and mineral nitrogen in the soil.2)The interaction between different cover crop species and incorporation promoted the development of bacteria(gram-positive and gram-negative),and further promoted the explosive growth of bacterivores,thus increasing the relative number of bacterial nematode eating.3)In in the two decomposition stages,the metabolic footprint of nematode was the highest when the maximum amount of cover crop residue was returned to the field,and the energy channels of soil debris food web were dominated by bacterial energy channels,with rapid turnover of nutrients.4)with the bean milk vetch(low ratio of carbon:nitrogen,more active resources),compared with the decomposition of the number increase,gramineae ryegrass(high ratio of carbon:nitrogen,the less active resources)when returning the biggest quantity can increase the quantity catching cicadas nematodes,improve the structure of nematode index and the concentration index and nematode community complexity of nematode community network structure is more stable,suggests that soil ecological system to a more mature stage of development.In conclusion,based on the classification of functional traits of cover crop,it was found that the growth of cover crop mainly affected the soil nematode community through biomass,carbon/nitrogen ratio,lignin content and nitrogen content of root system.At the same time,it was found that in the subsequent decomposition of cover crop residues and the growth of main crops,the residual effect of cover crop(biomass,ratio of plant carbon:nitrogen ratio,etc.)and the biomass of maize affected the nematode community and energy passage,indicating that the types of cover crop and the amount of returned farmland were the main factors affecting the soil nematode community.The effects of the interaction of these two factors on nematode were investigated through the control experiment.The results of this study on the effect of cover crop traits on the structure and function of soil food web can also provide a basis for the regulation and control of cover crop to guide the measures of ecological agriculture.