Effects of long-term cropping system and cropping sequence on the rhizosphere microbiota of Kimchi cabbage

Long-term monocropping can lead to an imbalance in soil nutrients and an increase in soil-borne diseases, which consequently cause significant reductions in crop yield. In the alpine regions of Korea, the production of Kimchi cabbage (Brassica rapa subsp. pekinensis (Lour.) Hanelt) faces increasing challenges. The scarcity of arable land has led to repeated monoculture practices. Additionally, rising temperatures and shallow, stony soils characteristic of sloped fields further limit sustainable cultivation. Although extensive research has examined the physicochemical differences in soil across various cropping systems, our understanding of rhizosphere microbial communities in Kimchi cabbage remains limited. In this study, we investigated the effects of three cropping systems - monoculture, rotation with soybean, and rotation with potato - on rhizosphere microbial structure in both field and pot conditions over nine or ten successive cropping cycles. The application of high-throughput sequencing to the analysis of bacterial 16 S rRNA and fungal ITS regions revealed significant effects of both cropping system and sequence on rhizosphere communities. The cropping sequence had the most significant influence on the microbial communities, accounting for 14% of the observed variance. Long-term cultivation was associated with reduced microbial diversity, particularly in the monoculture system. Community dissimilarity declined more rapidly under the monoculture system than under the rotation systems. Continuous Kimchi cabbage cultivation exhibited an increase in the abundances of Rhodanobacter, Ktedonobacteraceae, and Alternaria in comparison to the rotation treatments. The abundances of Sphingomonas, Terrabacter, Pseudarthrobacter, Trichocladium, and Botryotrichum decreased along the cropping sequence in the rhizosphere soil of the monoculture system. Although the cropping system had a modest effect, specific microbial groups were associated with monoculture cultivation. The cropping sequence exhibited a marked cumulative effect on the rhizosphere microbial diversity of Kimchi cabbage across all treatments. These findings provide a microbiota-based rationale for sustainable management strategies in Kimchi cabbage production systems.