Effects of continuous cropping of cassava on soil physicochemical properties and bacterial community succession

【Objective】The aim of this study was to investigate how continuous cropping of cassava affected the physicochemical properties of non-rhizosphere and rhizosphere soils,as well as the succession of bacterial communities,and thus providing a theoretical basis for understanding the formation of cassava continuous cropping obstacles. 【Method】The cassava variety South China 205 was continuously cultivated in an abandoned field for three years. The soil were sampled at cassava root tuber maturity stage(250 d after planting) in each year. Combining soil agrochemical analysis, highthroughput sequencing technology and bioinformatics methods, effects of continuous cassava on non-rhizosphere and rhizosphere soil physicochemical properties and bacterial group succession were studied. 【Result】The results showed that pH, organic matter, alkali-hydrolyzed nitrogen and available phosphorus contents of non-rhizosphere and rhizosphere soil of cassava were decreased and urease activity was increased in two and three years of continuous cropping compared with the first year of planting, and except available phosphorus content, the changes of other indexes reached significant level(P<0.05, the same below). Continuous cropping of cassava led to a decrease in the diversity and richness of soil bacterial communities. However,the decline rate in rhizosphere soil bacterial communities was slower than that in non-rhizosphere soils. There were significant differences in the classification and phylogenetic Beta diversity of non-rhizosphere and rhizosphere soil bacterial communities of continuous cropping cassava. The dominant bacterial phyla in non-rhizosphere and rhizosphere soils were Actinobacteriota,Proteobacteria,Chloroflexi,Firmicutes and Acidobacteriota. The main dominant bacterial genera were Bacillus,norank_f_Roseiflexaceae,norank_f_norank_o_Vicinamibacterales and norank_f_norank_o_Gaiellales. At the operational taxonomic unit(OTU)level,significant or extremely significant(P<0.01) differences were found in the composition of soil bacterial communities in non-rhizosphere and rhizosphere soils of cassava at different continuous cropping years. The structure of soil bacterial communities was mutually affected by soil physicochemical properties, the environmental factors affected bacterial community ranked as alkaline hydrolysis nitrogen content > organic matter content > pH > available phosphorus content > urease activity. 【Conclusion】Continuous cropping can lead to changes in non-rhizosphere and rhizosphere soil physicochemical properties, bacterial community diversity and richness, and soil physicochemical properties and bacterial community structure of cassava greatly deteriorate in the third year of continuous cropping. Soil physicochemical properties are correlated to structure of bacterial communities at certain extent. Notably,the decrease in the abundance of beneficial bacteria might be an important reason for the deterioration of soil bacterial community succession caused by cassava continuous cropping.