Bistability of rhizosphere microbiomes shapes phosphorus partitioning in river networks under water diversion.

Inter-basin water transfer projects are critical for mitigating water scarcity yet impose complex environmental disturbances, altering phosphorus (P) partitioning in recipient river networks. In these ecosystems, rhizosphere microbial communities (RMCs) act as biogeochemical engines regulating P partitioning among water, sediment, and biological phases. This regulatory capacity relies on structural and functional traits of RMC states. However, given their environmental sensitivity, RMCs are susceptible to water diversion disturbances. It remains unclear whether these disturbances drive state transitions and how these shifts reshape P partitioning. Here, we developed a stability landscape framework to characterize RMC states, identify their key environmental drivers, and examine effects on P partitioning in receiving river networks. Results revealed RMC bistability driven by the combination of the coefficient of variation of flow rate (CV_rate), turbidity, and temperature. One stable state maintained low water total P (WTP) and microbial biomass P (MBP), and high plant total P. This low-WTP state featured enrichment of Actinomycetota and Acidobacteriota, enhanced positive network cohesion, and abundant inorganic phosphorus solubilization genes (ppa, ppx). Conversely, the alternative state exhibited elevated WTP and MBP, enriching Cyanobacteriota and Bacteroidota, with simplified networks and enhanced organic phosphorus mineralization and transport genes (phoA, phnW, ugpAC, pstS). Furthermore, this stability landscape framework identified reference values for individual environmental drivers (temperature = 11.93°C, CV_rate = 5.93, turbidity = 21.92 NTU) to inform regulation favoring the low-WTP state. These findings provide a transferable quantitative framework, enabling water diversion operations to shift from reactive P pollution control toward proactive ecological regulation.