Fall dormancy seasonally drives alfalfa–soil interactions by modulating soil nutrient status and microbial community on the Loess Plateau, China

Aims Fall dormancy (FD) in alfalfa (Medicago sativa L.) is a physiological adjustment strategy that determines forage yield, winter survival rates and spring regrowth. This study aimed to explore whether FD could drive alfalfa–soil interactions by modulating soil nutrient status and the microbial community. Methods We investigated the root characteristics, soil nutrients and bacterial and fungal communities of alfalfa cultivars (dormant (D), semidormant (SD), and nondormant (ND)) during the growing season and dormant season on the Loess Plateau, China. Results Our results indicated that the total nitrogen (TN), soil organic carbon (SOC) and total phosphorus (TP) contents tended to increase with increasing FD level in the dormant season. The opposite trend was generally observed for TN, sucrase (SUC) activity and protease (PRO) activity in the growing season. Furthermore, our results demonstrated that FD more readily influences soil fungal than bacterial communities; moreover, both bacterial and fungal diversity indices were lower in the dormant season than in the growing season. There were no obvious differences in the microbial co-occurrence network in the growing season, whereas in the dormant season, the percentage of positive interactions increased with increasing FD level, while that of negative correlations decreased. Conclusions Our results, based on the selection of alfalfa cultivars of different FD types, highlight the importance of the FD-driven rhizosphere effects, which further influences nutrient cycling and the soil microbial community, especially during the dormant season. This study provides valuable information for understanding complex FD-driven plant–soil interactions in alfalfa cultivation.