Responses Of Orchard Soil Nutrients And Microbial Community To Different Covercropping Pattern

Soil microbial community plays a key role in the growth and yield of fruit trees and plays an important role in agricultural ecosystem.In recent years,due to the rapid development of Shaanxi fruit industry,the continuous popularization and improvement of science and technology,and people’s pursuit of a better life,the traditional orchard clear tillage system has been impacted.Clear tillage not only leads to the increase of human expenditure in orchards,but also leads to the ecological degradation of orchards,and the decline of soil fertility,the premature aging of fruit trees and the decline of fruit quality.It cannot meet the requirements of modern fruit production and development,and exposes the problems to be solved urgently in the local soil management system.At the same time,due to perennial clear tillage,the content of organic matter in orchard soil is low,and soil microorganisms degrade soil organic matter,resulting in the decline of soil fertility and sustainable development ability of domestic orchards.So far,few studies have evaluated the effects of different cover cropping systems on soil diazotrophic community in arid orchards on the Loess Plateau,and the effects of cover cropping on bacterial-fungal communities still need more research.Therefore,we studied the effects of 6-year-old cover cropping on soil bacteria,fungi,nitrogen fixing bacteria and soil nutrients in apple orchard.Three treatments were set up in this study: Trifolium repens L.(TR),Lolium perenne L.(LP)and clear tillage(CT).The 16 S r DNA,ITS and nif H functional gene fragments of soil after different treatments were analyzed by high-throughput sequencing to compare the diversity of soil microbial community and function,and the relationship between soil nutrients and microorganisms under different treatments.The main results of this study are as follows:(1)The composition and diversity of soil bacterial and fungal communities changed under different mulching treatments.The main composition of bacterial community was Proteobacteria and the main composition of fungal community was Ascomycota.TR and LP mulching improved the diversity of bacteria and fungi in soil,and the abundance of Actinobacteria in bacterial community structure was improved;the abundance of Glomera in the fungal community increased.The altered composition of the soil microbial community enhanced the ability of the bacterial community to secrete β-glucosidase and break down xylanase phyto-residues,which in turn increased soil enzyme activity and ultimately led to an increase in soil organic matter.The relative abundance of Basidiomycota increased due to the increase in plant apoplast after cover crops,which increased the lignin content of the soil.At the same time,cover cropping treatments improved Carbohydrate Metabolism,Enzyme Families,Transcription,Signaling Molecules and Interaction,Excretory System,Endocrine System,Biosynthesis of Other Secondary Metabolites.The bacterial-fungal molecular ecological network of cover cropping treatment was more complex,and the links between bacteria and fungi increased significantly,but increments among bacteria were more competitive,while increments among fungi were mostly cooperative.The collaborative relationship between bacteria and fungi also increased,which indicated that cover cropping was conducive to the energy,material and information flow.At the same time,through network analysis,we found that the key species were Cohnella,Arthrography and Novosphingobium for CT treatment;Luteitarea,Pseudofulvimonas and Microtrichales for TR treatment,;Pseudoxanthomonas,Byssovorax and Duganella for LP treatment.(2)Cover cropping changed the composition and diversity of soil nitrogen fixing bsacteria community.Anaeromyxobacterium was the main component of TR treatment,and Mesorhizobium was the main nitrogen fixing bacteria of LP treatment.Compared with the clear tillage treatment,the alpha diversity of nitrogen fixing bacteria in TR and LP treatment was generally reduced,which may be due to the stable composition of nitrogen fixing bacteria community and the screening of the most suitable nitrogen fixing bacteria due to the long-term specific single plant mulching.The main nitrogen fixing bacteria in TR treatment were Anaeromyxobacter,and the main nitrogen fixing bacteria in LP treatment were Mesorhizobium.The number of negative connections between nitrogen fixing bacteria communities was higher than that of positive connections,indicating that there was more competition among nitrogen fixing bacteria.Therefore,it was speculated that the reduction of nitrogen fixing bacteria diversity in apple orchard soil might promoted the frequency and degree of competition between nitrogen fixing bacteria.At the same time,through the network,we found that at the genus level,the nitrogen fixing bacteria module hubs included Azohydromonas,Anaeromyxobacter,Bradyrhizobium,Mesorhizobium and Rhizobium.(3)LP treatment increased soil total carbon,organic matter,moisture and C:N;TR treatment increased soil total carbon,total nitrogen,organic matter,available potassium,microbial biomass carbon and moisture.Both TR and LP cover cropping increased the contents of total carbon,organic matter and microbial biomass carbon in orchard soil.Soil organic matter,total carbon and ammonium nitrogen were the decisive environmental factors determining the composition of soil bacterial community,while microbial biomass nitrogen,total nitrogen and C:N had a greater impact on the composition of fungal community.Soil β-D-Glucosidase contents of TR and LP treatments increased,while TR treatment increased the content of cellobiose hydrolase in soil.For nitrogen fixing bacteria,the influence of environmental factors on nitrogen fixing bacteria community was as follows: total carbon >organic matter > available phosphorus > ammonium nitrogen > nitrate nitrogen.