Rooting for hyphae: functional persistence of water transport from arbuscular mycorrhizal fungi to plants during soil drying

Abstract Aims Arbuscular mycorrhizal fungi (AMF) are widely thought to support plant water uptake during drought, but whether their hyphae remain hydraulically functional once soil hydraulic conductivity collapses under severe drying, and how this depends on soil texture, remains unresolved. We tested whether AMF can maintain hydraulic functionality and transport water to plants under severe soil drying. Methods A simple conceptual framework comparing soil and hyphal hydraulic conductivities motivated the study. We used a split-pot system with a physical air gap that isolated AMF-mediated water transport from soil to the roots and applied stable water isotope ( 2 H 2 O) tracing. Maize plants colonized by Rhizophagus irregularis were subjected to three soil moisture regimes (well-watered, moderately dry, and severely dry; matric potentials from −0.01 to below −8 MPa). Results 2 H-labeled water was detected in plant transpiration across all soil moisture treatments, including the severely dry conditions, demonstrating that hyphae remained connected to the plant and continued to transport water under conditions in which bulk soil water flow was strongly reduced. The conceptual framework, which compares soil and hyphal hydraulic conductivities, situates this finding within a broader, texture-dependent prediction that AMF water transport becomes increasingly relevant as soils dry. Conclusions Our results provide strong experimental evidence that AMF hyphae can remain hydraulically functional and transport water to plants even under extreme soil drying. These findings support the functional persistence of AMF water transport during drought, and provide an empirical anchor for the broader, texture- and moisture-dependent role of AMF in plant water uptake.