Relationship between phosphorus stoichiometric homeostasis and deepwater adaptability of submerged macrophytes in Erhai Lake, China: Insights from allometric plasticity.

The state transition theory suggests that the decline of submerged macrophytes in shallow lakes is closely associated with reduced stoichiometric homeostasis, particularly phosphorus homeostasis (H P ). The degradation typically progresses from deeper to shallower regions, indicating a potential positive correlation between the deepwater adaptability (DA) and H P values of submerged macrophytes. Here, we investigated the distribution pattern of submerged macrophytes across different water depths of Erhai Lake to test this hypothesis. The results revealed a significant positive correlation between the DA and H P values of submerged macrophytes. Allometric analysis indicated that the morphological plasticity of submerged macrophytes was linked to their H P . Species with higher H P values, like Potamogeton maackianus, had robust plasticity strategies, particularly "real plasticity", that enabled them to cope with deeper water stress. In contrast, species with lower H P values (Ceratophyllum demersum and Hydrilla verticillata) experienced nutrient declines, which hindered their adaptation. Additionally, species with higher H P values exhibited closer connections within the plant traits-environment network, indicating that their morphological plasticity adjustments allow better adaptation to the environmental changes caused by increasing water depth. These results confirm the relationship between DA and H P in submerged macrophytes and explain the mechanisms underlying the correlation, thus expanding regime shift theory.