Routes to roots: direct evidence of water transport by arbuscular mycorrhizal fungi to host plants

• Published in: The New phytologist Vol. 236; no. 1; pp. 210 - 221
• Main Authors: Kakouridis, Anne, Hagen, John A., Kan, Megan P., Mambelli, Stefania, Feldman, Lewis J., Herman, Donald J., Weber, Peter K., Pett‐Ridge, Jennifer, Firestone, Mary K.
• Format: Journal Article
• Language: English
• Published: England Wiley Subscription Services, Inc 01.10.2022; Wiley-Blackwell
• Subjects: Air; Air gaps; arbuscular mycorrhizal fungi; Arbuscular mycorrhizas; BASIC BIOLOGICAL SCIENCES; Cell membranes; Dyes; fluorescence microscopy; Fluorescent dyes; Fluorescent indicators; Fungi; Host plants; Hyphae; hyphal transport; Microcosms; nutrient transport; Plants; plant–microbe interactions; plant–water relations; Rhizophagus intraradices; Roots; stable isotopes; Transpiration; Transport; Water; Water flow; Water stress; Water transport; stable isotopes; Rhizophagus intraradices; plant-microbe interactions; plant-water relations; arbuscular mycorrhizal fungi (AMF); hyphal transport; fluorescence microscopy; nutrient transport
• ISSN: 0028-646X; 1469-8137
• DOI: 10.1111/nph.18281

Summary Arbuscular mycorrhizal fungi (AMF) can help mitigate plant responses to water stress, but it is unclear whether AMF do so by indirect mechanisms, direct water transport to roots, or a combination of the two. Here, we investigated if and how the AMF Rhizophagus intraradices transported water to the host plant Avena barbata, wild oat. We used two‐compartment microcosms, isotopically labeled water, and a fluorescent dye to directly track and quantify water transport by AMF across an air gap to host plants. Plants grown with AMF that had access to a physically separated compartment containing 18O‐labeled water transpired almost twice as much as plants with AMF excluded from that compartment. Using an isotopic mixing model, we estimated that water transported by AMF across the air gap accounted for 34.6% of the water transpired by host plants. In addition, a fluorescent dye indicated that hyphae were able to transport some water via an extracytoplasmic pathway. Our study provides direct evidence that AMF can act as extensions of the root system along the soil–plant–air continuum of water movement, with plant transpiration driving water flow along hyphae outside of the hyphal cell membrane.