Arbuscular mycorrhizal fungi (AMF) have been presumed to ameliorate crop tolerance to drought. Here, we review the role of AMF in maintaining water supply to plants from drying soils and the underlying biophysical mechanisms. We used a soil-plant hydraulic model to illustrate the impact of several AMF mechanisms on plant responses to edaphic drought. The AMF enhance the soil's capability to transport water and extend the effective root length, thereby attenuating the drop in matric potential at the root surface during soil drying. The synthesized evidence and the corresponding simulations demonstrate that symbiosis with AMF postpones the stress onset limit, which is defined as the disproportionality between transpiration rates and leaf water potentials, during soil drying. The symbiosis can thus help crops survive extended intervals of limited water availability. We also provide our perspective on future research needs and call for reconciling the dynamic changes in soil and root hydraulics in order to better understand the role of AMF in plant water relations in the face of climate changes.

Chair of Root Soil Interaction School of Life Sciences Technical University of Munich Freising Germany

Chair of Soil Physics Bayreuth Center of Ecology and Environmental Research University of Bayreuth Bayreuth Germany

Department of Horticulture Faculty of Agriculture University of Khartoum Khartoum North Sudan

Department of Mycorrhizal Symbioses Institute of Botany of the Czech Academy of Sciences Průhonice Czech Republic

Humboldt Universität zu Berlin Thaer Institute Division Urban Plant Ecophysiology Berlin Germany

Laboratory of Fungal Biology Institute of Microbiology Czech Academy of Sciences Prague Czech Republic

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Soil compaction reversed the effect of arbuscular mycorrhizal fungi on soil hydraulic properties