Unfolding the dynamics of ecosystems undergoing alternating wet-dry transitional states

A significant fraction of Earth's ecosystems undergoes periodic wet-dry alternating transitional states. These globally distributed water-driven transitional ecosystems, such as intermittent rivers and coastal shorelines, have traditionally been studied as two distinct entities, whereas they constitute a single, interconnected meta-ecosystem. This has resulted in a poor conceptual and empirical understanding of water-driven transitional ecosystems. Here, we develop a conceptual framework that places the temporal availability of water as the core driver of biodiversity and functional patterns of transitional ecosystems at the global scale. Biological covers (e.g., aquatic biofilms and biocrusts) serve as an excellent model system thriving in both aquatic and terrestrial states, where their succession underscores the intricate interplay between these two states. The duration, frequency, and rate of change of wet-dry cycles impose distinct plausible scenarios where different types of biological covers can occur depending on their desiccation/hydration resistance traits. This implies that the distinct eco-evolutionary potential of biological covers, represented by their trait profiles, would support different functions while maintaining similar multifunctionality levels. By embracing multiple alternating transitional states as interconnected entities, our approach can help to better understand and manage global change impacts on biodiversity and multifunctionality in water-driven transitional ecosystems, while providing new avenues for interdisciplinary studies. Our framework proposes that water-driven transitional ecosystems experience periodic shifts between aquatic and terrestrial states within a single interconnected meta-ecosystem, driven by temporal water availability. Biological covers like aquatic biofilms and biocrusts play a central role, undergoing successional dynamics in response to wet-dry transitions, impacting biodiversity and ecosystem functioning. These impacts, especially considering the risk to become a stable dry ecosystem under the global change context, pose threats to the contribution of water-driven transitional ecosystems to global biogeochemical cycles, climatic stability, and human welfare.image