Root growth and presence of Rhizophagus irregularis distinctly alter substrate hydraulic properties in a model system with Medicago truncatula

Richard Pauwels,David Püschel,Michael Bitterlich,Jan Graefe,Jan Jansa,Anja Müller,Steffen Kolb

doi:10.1007/s11104-020-04723-w

Abstract

AimWe investigated how substrate hydraulic properties respond to the presence of arbuscular mycorrhizal fungi (AMF) in root-containing and root-free substrate zones in a Medicago truncatula-Rhizophagus irregularis model system.MethodsBefore planting, two compartments constructed from standard soil sampling cores (250 cm3) were implanted into non-mycorrhizal and mycorrhizal pots containing a sand-zeolite-soil mix. One compartment allowed root penetration (1 mm mesh cover) and the other only hyphal ingrowth (42 μm mesh cover). After eight weeks of growth under maintenance of moist conditions, the cores were subjected to water retention measurements. Additionally, we measured water retention of bare substrates before and after drying events to check for successful maintenance of moist conditions in pots.ResultsDrying of bare substrates decreased water retention, but planting at least sustained it. The parameters of water retention models responded linearly to root morphological traits across mycorrhizal and non-mycorrhizal substrates. Hyphae-only colonization comparatively affected the course of water retention in ways that suggest increased pore space heterogeneity while maintaining water storage capacity of substrates.ConclusionsHence, water contents corresponded to different substrate matric potentials in non-mycorrhizal and mycorrhizal pots. We conclude that changes to water retention in AMF colonized substrates can contribute to a widely observed phenomenon, i.e. that mycorrhizal plants differ in their moisture stress response from non-mycorrhizal plants.

Highlights

Research on arbuscular mycorrhizal symbioses repeatedly reported that non-mycorrhizal plants and plants colonized by arbuscular mycorrhizal fungi (AMF) show distinct water consumption rates and physiological responses to certain moisture levels in the atmosphere and soil (Augé 2001, 2004; Augé et al 2015; Bitterlich et al 2019)
This was expected as colonization of cores required de novo colonization by either roots or AMF hyphae or it was related to certain degradation of AMF since the molecular quantification of AMF in cores took place a few days later after water retention measurements were terminated
The pore space harboring mycorrhizal hyphae can exceed their volume by dimensions while water transport properties in it being modulated to a substantial degree

Summary

Introduction

Research on arbuscular mycorrhizal symbioses repeatedly reported that non-mycorrhizal plants and plants colonized by arbuscular mycorrhizal fungi (AMF) show distinct water consumption rates and physiological responses to certain moisture levels in the atmosphere and soil (Augé 2001, 2004; Augé et al 2015; Bitterlich et al 2019). Technological advancements have allowed to prove that arbuscular mycorrhizal plants differ from their non-mycorrhizal counterparts in their physiological and metabolic response to soil moisture, sometimes indicating a higher metabolic capacity to cope with water stress or to take up water (Aroca et al 2007; Bárzana et al 2014; Bitterlich et al 2018c; Porcel et al 2006; Porcel and Ruiz-Lozano 2004; Ruiz-Lozano et al 1995; Zou et al 2019). Roots and soil fungi as members of the soil biota are considered integral contributors in a self-organizing system that modulates soils towards more porous, ordered and aggregated habitats with distinct (water) transport properties

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