Regulatory Mechanisms for the Stability of K/R Strategy Microbial Communities in Urban Groundwater Sources: Machine Learning Unveils the Driving Mechanism of the Bistable Structure

Microbial communities in urban groundwater play a key role in metabolic networks and water quality dynamics, yet the ecological strategies and stability evolution of bacterial systems remain poorly understood. This study combines rrn operon copy number, machine learning, and potential landscape analysis to reveal multistable structures and stability regulation in bacterial communities under K- and r-strategies. Groundwater communities are predominantly K-strategists, with r-strategists enriched where external nutrients enter. Both strategies show distinct bistable states (A/B), shaped by different environmental drivers. NH4+–N (0.17–1.42 mg·L–1) and COD (1.58–2.78 mg·L–1) were identified as transition thresholds for K- and r-strategies, respectively, indicating alternative stable states. K-state A is more stable under low nitrogen, while K-state B loses stability under high nitrogen. In contrast, r-state A maintains diversity and function under low carbon, whereas r-state B becomes unstable with increased carbon input. Path analysis reveals that α-diversity negatively regulates K-strategy stability (−0.77, p < 0.001), while β-diversity positively supports r-strategy stability (0.77, p < 0.001). K-strategists rely on environmental filtering and competition for stability; r-strategists use metabolic complementarity and rapid responses for adaptability. These findings offer a quantitative framework for understanding microbial stability in groundwater under nutrient and pollution stress.