Abstract
The continuous cropping of sugar beet can result in soil degradation and a decrease in the sugar beet yield and quality. However, the role of continuous sugar beet (Beta vulgaris L. var. saccharifera) cropping in shaping the structure and function of the rhizosphere microbial community remains poorly investigated. In this study, we comparatively investigated the impact of different numbers of years of continuous sugar beet cropping on structural and functional changes in the microbial community of the rhizosphere using high-throughput sequencing and bioinformatics analysis. We collected rhizosphere soils from fields continuously cropped for one-year (T1), five-year (T5), and thirty-year (T30) periods, as well as one bulk soil (T0), in the Xinjiang Uygur Autonomous Region. The results demonstrated that continuous sugar beet cropping resulted in a significant decline in the community diversity of soil bacterial and fungal populations from T1 to T5. With continuous change in the structure of the microbial community, the Shannon diversity and observed species were increased in T30. With an abundance of pathogenic microbes, including Acidobacteria, Alternaria, and Fusarium, that were highly enriched in T30, soil-borne diseases could be accelerated, deduced by functional predictions based on 16S rRNA genes. Continuous sugar beet cropping also led to significant declines in beneficial bacteria, including Actinobacteria, Pseudomonas spp., and Bacillus spp. In addition, we profiled and analyzed predictive metabolic characteristics (metabolism and detoxification). The abundance of phenolic acid decarboxylase involved in the phenolic acid degradation pathway was significantly lower in groups T5 and T30 than that in T0 and T1, which could result in the phenolic compounds becoming excessive in long-term continuous cropping soil. Our results provide a deeper understanding of the rhizosphere soil microbial community’s response to continuous sugar beet cropping, which is important in evaluating the sustainability of this agricultural practice.
Highlights
Sugar beet (Beta vulgaris L. var. saccharifera) is an important crop in temperate climates, providing approximately 30% of the world’s annual sugar production [1]
We found that the abundance of OTU17 (Fusarium oxysporum) was significantly higher in the rhizosphere fungal community of continuous cropping soils than in that of bulk soil (Dataset S11), suggesting that the continuous cropping of sugar beet increased the potential pathogenic fungal density in the soil
This study showed significant changes in the microbial community composition at different taxa levels and the diversity of rhizosphere soil under different years of continuous sugar beet cropping
Summary
Sugar beet (Beta vulgaris L. var. saccharifera) is an important crop in temperate climates, providing approximately 30% of the world’s annual sugar production [1]. Continuous cropping has aggravated more problems in sugar beet systems, including soil-quality degradation, crop-yield and sugar content reduction, and plant disease intensification [4]. Continuous obstacles to the cropping of sugar beet could become severe due to the shortage of cultivated land resources in the Xinjiang area, as well as the imperfect cultivation management system and the constraints of the production environment. Comprehensive prevention and control technologies have been reported to be effective measures for alleviating such problems, including the use of improved seeds, new fertilizers, environmentally-friendly pesticides, and soil conditioners [6,7,8]. Studies on the control of obstacles to continuously cropping sugar beet using comprehensive solutions and key agricultural technologies are still rare
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