Abstract: Celery is a characteristic vegetable in Ningxia cold region, and its large-scale planting inevitably leads to the prominent obstacle of continuous cropping. In order to reveal the diversity characteristics of microbes in celery rhizosphere soil and the difference of community structure with planting years, author used Illumina Novaseq-PE250 sequencing platform to sequence 16S V3V4 region and ITS1 region of celery rhizosphere soil samples after planting for one year (CA), continuous cropping for two years (CB) and continuous cropping for three years (CC), and made bioinformatics analysis.The results showed that the soil bacterial diversity decreased gradually with the extension of continuous cropping years. The Chao 1 index decreased from 8509.41 in the first year to 6314.09 in the third year.The CA Shannon index was the highest at 11.48 and the CC was the lowest at 11.08.The abundance of beneficial bacteria such as Deltaproteobacteria and Gemmatimonadetes in soil bacteria and Rokubacteriales, Blastococcus and Solirubrobacter in them decreased. The diversity index and richness index of soil fungi first decreased and then increased with the increase of continuous cropping years, which showed that the Chao 1 index of CA and CB was 505.44 and 264.66, while CC was 443.92, the Shannon index of CA and CB was 5.98, 4.93, and CC was 5.61, and there were significant differences between continuous cropping years. At the same time, there are significant differences among soil fungi, such as Sordariomycetes, Lophotrichus, Melanospora and other dominant genera. The results of microbial principal coordinate component analysis showed that there was strong heterogeneity between CC and other treatments. The function prediction analysis of PICRUSt2 showed that bacteria in the rhizosphere soil of celery mainly had 7 major categories of primary functional layers, with the highest relative abundance of Amino Acid Biosynthesis, fungi had 5 major categories of primary functional layers, and the highest relative abundance of Nucleoside and Nucleotide Biosynthesis. At the same time, there were significant differences between multiple metabolic pathways in different years of continuous cultivation of celery. To sum up, celery continuous cropping will reduce the richness and diversity of rhizosphere soil flora, change the flora structure, and lead to the imbalance of rhizosphere micro-ecological environment, thus causing related continuous cropping obstacle diseases. Among them, the microbial indices changed the most when celery was continuously cropped for three years. Therefore, it is recommended that the celery industry in the southern mountainous areas of Ningxia should be continuously cropped for no more than two years as a field planting mode.

Key words: Celery, Continuous croping year, Rhizosphere soil microorganism, High-throughput sequencing, PICRUSt2 functional prediction