Water from the Air: The Role of Foliar Uptake in Science, Education, and Environmental Policy

The traditional representation of the water cycle often overlooks the active role of vegetation in absorbing atmospheric moisture, rendering it incomplete. This oversight is particularly evident in the classic soil-plant-atmosphere continuum (SPAC), which describes a unidirectional water flow from soil to atmosphere. However, increasing evidence highlights reverse fluxes, such as the downward movement of water from the atmosphere to plants and potentially into the soil. One key mechanism enabling this is foliar water uptake (FWU), through which leaves directly absorb moisture from sources like fog, facilitating rapid hydration and internal redistribution of water. Despite growing documentation in eco-physiological research, FWU remains largely absent from broader scientific discourse, public policy, education, and ecosystem management frameworks. Neglecting FWU and fog as hydrological inputs limits our understanding of water dynamics in ecosystems, especially under climate change scenarios that alter fog and dew formation patterns. This viewpoint emphasizes the urgency of integrating FWU into ecological models, science education, and environmental decision-making. By rethinking the water cycle through this lens, we highlight a transformative pathway to enhance conservation strategies, understanding plant functional traits related to climate change, and the science-policy-society interface.

Keywords:
Decision-making; Ecohydrology; Fog; Incomplete Water Cycle