Abstract: The objective is to compare the differences in bacterial communities in soil between for the continuous cropping of lettuce and lettuce-spinach rotation. Soil samples were collected from depths of 0-20 cm. High-throughput sequencing technology was used to analyze the bacteria present in soil samples before and after lettuce planting. Sequencing data presented that 46 865 effective sequences were received after quality filter,and 21 692 OTUs were obtained through biological information on similar levels of 97% OTU statistical analysis. Heatmap and community composition analysis showed that bacteria 40 phylum,89 classes,190 orders,371 families,and 693 genera in the samples were detected,and the proportion of Proteobacteria,Firmicutes and Actinomycetes in the continuous process gradually reduced while the change in rotation process was stable. Moreover,the beneficial bacterial genera,including Agromyces,Arthrobacter,Flavobacterium,Lysobacter and Microbacterium,gradually became dominant in the rotation soil samples. The yield of rotating lettuce and catalase activity increased compared with that of continuous cropping. The results of principal component analysis demonstrated that there was significant difference between soil samples in rotation and continuous cropping. After the fifth consecutive planting of lettuce,the yield and catalase activity of lettuce decreased 24.1% and 20.7% respectively,and the obstacles for continuous cropping appeared;while the yield and catalase activity of lettuce in rotation were improved 49.6% and 10.5% respectively,compared with that in continuous cropping. In conclusion,there is the rich diversity of beneficial bacteria in rotating lettuce with spinach,and which increases with the increasing of rotating process,and partially alleviates the problems that occur during lettuce cultivation.

Key words: bacteria diversity, lettuce, rotation, continuous cropping