The Soil-Plant Coupling Principle (SPCP): A Conceptual Framework for Diagnosing Hidden Ecosystem Vulnerability.

We introduce the Soil-Plant Coupling Principle (SPCP), a conceptual framework proposing that ecosystem stability emerges from the integrity of biological interactions rather than the condition of individual ecosystem components. Although current ecological assessments primarily rely on soil properties, plant performance, and microbial diversity, growing evidence indicates that ecosystems can remain apparently functional while progressively losing the coordination among processes that sustain resilience. This gap limits the ability of conventional diagnostics to capture interactional changes underlying early ecosystem vulnerability. Unlike ecosystem multifunctionality and resilience, which primarily describe the provision of multiple functions and the capacity to resist or recover from disturbance, respectively, SPCP focuses on the coordination among the processes that sustain these functions and resilience. SPCP reframes ecosystem degradation as progressive decoupling among carbon allocation, nutrient cycling, hydrological processes, and microbial interactions at the soil-plant interface. By integrating recent advances in soil ecology, plant physiology, microbiome science, ecological networks, and biogeochemistry, the framework provides a unified conceptual basis for understanding how interactional connectivity regulates ecosystem resilience. The objectives of this Perspective are to: (i) establish the theoretical basis for viewing ecosystem stability through soil-plant coupling; (ii) define the core dimensions of coupling integrity; and (iii) outline how coupling integrity could be operationalized using structural, functional, and interaction-based indicators. We further discuss the potential of coupling integrity as an early-warning property and identify key limitations and research needs for testing and validating the framework. By proposing an integrative and potentially testable framework, the manuscript provides a new lens for understanding ecosystem vulnerability and resilience across scales.