Chapter 17 - Soil Water Retention and Availability as Influenced by Mycorrhizal Symbiosis: Consequences for Individual Plants, Communities, and Ecosystems

Abstract

Soil water retention capacity, hydraulic conductivity, and permeability are primarily determined by texture (sand, silt, clay contents), structure (bulk density and porosity), and organic matter content. Mycorrhizal fungi play a subtle but important role in shaping the hydraulic properties of soils through multiple direct and indirect mechanisms related to mycorrhizal-induced changes in soil structure and organic matter content. A majority of studies report that the presence and/or abundance of mycorrhizal mycelia correlates positively with soil water-retention capacity, hydraulic conductivity, and infiltration capacity, and negatively with soil water erodibility, although further research in this area is warranted. Direct mechanisms include mycorrhizal enhancement of soil aggregation and porosity, enhanced soil organic matter accumulation resulting from hyphal carbon inputs to soil and protection of labile soil organic matter pools inside aggregates, mycorrhizal inhibition of soil organic matter decomposition through competitive interactions with other soil microbial guilds, and mycorrhizal regulation of soil water repellency. At the ecosystem scale, indirect (plant-mediated) mechanisms may be even more important than direct mechanisms, given that mycorrhizal enhancement of plant growth and plant community diversity and productivity stimulates soil organic matter accumulation and soil aggregation, porosity, and water retention.