Adaptability Of Different Dwarf Rootstocks And Differences In Soil Microbial Communities Under Repeated Apple Replant Disease

Apple replant disease is widely distributed all over the world,which seriously restricts the development of the apple industry.Overcoming the replanting disease is the key to promoting the development of the world apple industry.At present,it is generally believed that the selection of local resistant rootstocks is one of the most effective methods.Therefore,this study selected the apple orchard in Qianyang County,Baoji City,Shaanxi Province as the research material.Firstly,the effects of different years of apple orchard planting on soil microorganisms and soil nutrients were analyzed.Then,on the basis of clarifying the succession characteristics of soil microbial communities in apple orchards with different tree ages,comparing and studying the tolerance of different apple rootstocks to replant disease soil(20-year orchard planting),the effects of replant disease on bacterial and fungal communities in the rhizosphere soil of different rootstocks were analyzed.In order to explore the microbiological mechanism and effective coping strategies of apple replant disease from the perspective of microbial community.The main findings of this study include:1.With the increase of planting years,the content of major elements nitrate nitrogen,available phosphorus and available potassium in the soil;the content of trace elements manganese,zinc and boron showed an upward trend,and the content of soil organic carbon showed a trend of first decreased and then increased.The activities of alkaline phosphatase and catalase in apple orchard soil in each year were lower than those in control soil,showing a trend of first increase and then decrease,and these indicators were significantly correlated with bacterial community.Soil available phosphorus,available potassium,zinc,boron and dissolved organic carbon content and alkaline phosphatase activity were significantly associated with fungal communities.The nitrogen content of leaves showed a significant upward trend from low to middle age;the calcium content of trace elements first decreased and then increased,the magnesium content decreased significantly,and the iron and zinc content increased first and then decreased.With the increase of apple planting years,the Richness of soil bacterial community Alpha diversity did not change significantly,while the Richness of fungi community Richness Chao1 and ACE index increased firstly and then decreased,which were lower than those of the control.The PCo A results showed that the soil microbial community structure changed significantly after apple planting,and the difference in community structure increased with the increase of planting years.2.Compared with the farmland soil,the plant height,whole plant fresh weight,aboveground fresh weight and aboveground dry weight of rootstock M9-T337 in the replant disease soil were significantly reduced,and the plant height of rootstock M26 was significantly reduced,while that of Qingzhen No.1 was significantly reduced.There was no significant change in each growth index;The photosynthetic rates of M9-T337 and M26 were significantly inhibited in the soil of replant disease orchards,while the photosynthetic rate and chlorophyll content of Qingzhen No.1 were not significantly different.In general,the three rootstocks were Qingzhen No.1,M26 and M9-T337 in order from strong to weak.3.The richness and diversity of soil bacterial communities in orchards planted with different rootstocks were higher than those in farmland soils.Compared with the control farmland soil,the rhizosphere soil microbial community structure of the three rootstocks planted in the orchard soil was significantly changed.The relative abundances of Proteobacteria,Cyanobacteria and Bacteroidota in the rhizosphere soil of the three rootstocks decreased,while the relative abundances of Chloroflexi,Gemmatimonadota and Firmicutes increased slightly.the bacterial community interaction was enhanced,resulting in the response and resistance to replant disease.4.Compared with the control farmland soil,replant diseased soil had no significant effect on the Alpha diversity of the rootstock rhizosphere soil fungal community,but had an important impact on the fungal community structure.Compared with the control soil,the relative abundance of Mortierellomycota in the rhizosphere soil of the three rootstocks planted in the replant diseased soil was decreased,and the relative abundance of Basidiomycota was increased.The rhizosphere soil fungi co-occurrence network of the three rootstocks grown in apple orchard soil was more complex than the co-occurrence network of the three rootstocks grown in farmland soil,indicating enhanced fungal community interactions that produced responses to continuous cropping obstacle stress with resistance.In summary,with the increase of apple tree planting years,the apple orchard soil enzyme activity,nutrient content,microbial community and leaf mineral element content all changed regularly.The three rootstocks were Qingzhen No.1,M26 and M9-T337 in order from strong to weak.Compared with the control farmland soil,the rootstock rhizosphere soil microbial community structure,composition,function and co-occurrence network characteristics changed in the replant diseased orchard soil.