Continuous cropping alters rhizosphere microbial communities and soil properties reducing Curcuma Kwangsiensis yield

Curcuma kwangsiensis is a medicinal plant endemic to China with significant economic and medicinal value. In agricultural practice, it is typically harvested after one year of cultivation. However, continuous cropping has severely constrained the development of the C. kwangsiensis industry. To elucidate the effects of continuous cropping on the yield and rhizosphere soil environment, this study systematically investigated the effects of continuous cropping on C. kwangsiensis yield, rhizosphere soil physicochemical properties, enzyme activities, and microbial communities through field experiments. The results showed that continuous cropping significantly reduced C. kwangsiensis yield by 58.87%. It decreased soil pH while increasing the accumulation of soil nutrients including organic carbon, total nitrogen, total phosphorus, total potassium, available phosphorus, available potassium, and available nitrogen, but significantly decreased the activities of soil enzymes such as phosphatase, urease and catalase. Moreover, continuous cropping enhanced both the abundance and diversity of bacterial and microeukaryotic communities. It significantly increased the relative abundance of Planctomycetota, which became the dominant bacterial phylum, while also significantly increasing the relative abundances of the predominant microeukaryotic phyla Ciliophora and Cercozoa. Redundancy analysis revealed that pH was the most important factor affecting microbial community composition. Continuous cropping of C. kwangsiensis reduced soil pH, altered soil physicochemical properties and enzyme activities, and restructured microbial communities. The bacterial co-occurrence networks revealed a shift from a relatively compact and clustered structure at the initial stage to a larger and more complex network with continuous cropping, characterized by higher interaction density but reduced local clustering. The fungal networks shifted from a highly compact structure in Y0 to more expanded but less cohesive architectures in Y1 and Y2. SEM (Structural Equation Modeling) analysis shows that during continuous cropping, soil enzyme activity was the key influencing factor, which was closely related to microbial diversity and the availability of nitrogen and phosphorus, and there was a positive feedback effect. These changes collectively explain the yield reduction in C. kwangsiensis, providing a critical theoretical foundation for protecting its rhizosphere soil ecosystem and ensuring sustainable cultivation practices.