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

TL;DR

This study found that arbuscular mycorrhizal fungi do not improve water uptake in tomato and pea plants during drought.

Contribution

The study provides direct evidence that AM fungi do not enhance root hydraulic conductance in crops under drought.

Findings

AM colonization had no positive impact on root hydraulic conductance in tomato and pea under drought conditions.

Improved drought tolerance in AM plants is likely due to other physiological mechanisms, not increased water uptake.

Abstract

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 (Kr), thereby facilitating more efficient water uptake under soil drying, though this mechanism remains highly debated. Here, we measured Kr 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 Kr 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.

Arbuscular mycorrhizal symbiosis had no effect on root hydraulic conductance in 2 major crops, suggesting it does not improve drought tolerance by increasing water uptake.

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