Dynamic Changes in Rhizosphere Microbial Communities of Watermelon During Continuous Monocropping with Gravel Mulch

Xisha melon is a selenium-rich watermelon variety cultivated in semi-arid regions of north-central China as a primary economic crop. However, continuous monocropping has led to a notable increase in fusarium wilt disease incidence, and efficient control strategies are yet to be established. This work aims to investigate the biotic and abiotic factors influencing the population dynamics of rhizosphere microbial communities during continuous monocropping. Soil samples were collected from the rhizosphere of healthy watermelon grown in fields after 1, 3, 5, 10, 18, and 23 years of continuous monocropping, along with samples from nearby uncultivated land as a reference control. The soils were characterized by analysis of chemical properties and high-throughput sequencing of ribosomal amplicons targeting bacteria and fungi. The sequence data were then subjected to vigorous statistical analysis, including structural equation modelling. The data consistently revealed a general trend of increasing bacterial diversity but decreasing fungal diversity during continuous monocropping. Specifically, concerning the Fusarium population, its relative abundance decreased from 4.41% in the uncultivated soil to 0.61% in rhizosphere soil after 23 years of continuous monocropping, with nitrate-nitrogen being the most influential determining factor. Bacillus was among the bacterial genera enriched by continuous cropping. Our data collectively reveal that continuous watermelon cropping led to significant shifts in both bacterial and fungal communities, resulting in a decline of the Fusarium population in the rhizosphere. Furthermore, our findings suggest the potential roles of nitrate fertilization in manipulating the soil microbiome for efficient control of the fusarium wilt disease.