Fungal highways to water: Mechanisms of drought tolerance in arbuscular and ectomycorrhizal symbioses.

Drought is an increasingly important constraint on plant productivity, affecting agricultural yields, forest dynamics, and ecosystem functioning worldwide. Mycorrhizal symbioses formed by arbuscular (AM) and ectomycorrhizal (EcM) fungi are key regulators of plant responses to water limitation, influencing water acquisition, transport, and maintenance of plant water status at the soil-plant interface. This review synthesizes current knowledge of the mechanistic pathways through which mycorrhizal associations enhance plant drought tolerance. We distinguish between direct hydraulic contributions, including expanded soil exploration via extraradical hyphal networks, hyphal water uptake, redistribution, and modifications of rhizosphere hydraulic properties, and indirect physiological and biochemical effects, such as changes in root system architecture, regulation of aquaporins, osmotic adjustment, antioxidant capacity, and phytohormonal signaling. Particular emphasis is placed on structural and functional differences between AM and EcM symbioses. We examine how contrasting intraradical interfaces (i.e., arbuscules versus Hartig net) and extraradical networks influence water movement, plant hydraulic conductance, and whole-plant performance under drought. We assess the implications of these processes for agriculture and forestry, highlighting context-dependent fungal-plant compatibility, maintenance of diverse mycorrhizal communities, and management practices that preserve soil structure and mycorrhizal networks. Despite substantial evidence that mycorrhizal fungi improve plant performance under water deficit, their quantitative contributions to plant water transport and growth remain insufficiently resolved, particularly in EcM-dominated systems. Addressing these knowledge gaps will require integrative, multi-scale approaches linking molecular regulation, root and hyphal hydraulics, and ecosystem-level water fluxes. Such advances are critical for predicting vegetation responses to intensifying drought conditions under global change.

© 2026. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.