Arbuscular mycorrhizal colonization does not improve root hydraulic supply in tomato and pea

Arbuscular mycorrhizal (AM) fungi are known to enhance plant drought tolerance, but the physiological mechanism behind this benefit remains unclear. One explanation is that AM colonization improves root hydraulic conductance (K_r), thereby facilitating more efficient water uptake under soil drying, though this mechanism remains highly debated. Here, we measured K_r in tomato (Solanum lycopersicum L.) and pea (Pisum sativum L.) with and without AM using a noninvasive rehydration technique under soil drying, and this was complemented with the evaporative flux method under hydrated conditions. AM colonization was manipulated either through soil sterilization or by using nonmycorrhizal mutants, ensuring precise control of AM status. In both species, AM colonization had no positive impact on K_r under both well-hydrated and drought conditions. The finding suggests that the improved drought performance often observed in AM-colonized plants is not due to enhanced root water transport capacity. Instead, AM-induced benefits under drought may be mediated by other physiological adjustments.