Variable effects of arbuscular mycorrhizal fungal inoculation on physiological and molecular measures of root and stomatal conductance of diverse Medicago truncatula accessions

Abstract

Association with arbuscular mycorrhizal fungi (AMF) can impact on plant water relations; mycorrhizal plants can exhibit increased stomatal conductance (gs) and root hydraulic conductance (normalized to root dry weight, Lo), and altered expression of aquaporins (AQP). Many factors regulate such responses; however, plant intraspecific diversity effects have yet to be explored. Twenty geographically diverse accessions of Medicago truncatula were inoculated with the AMF Funneliformis mosseae or mock-inoculated, and grown under well-watered conditions. Biomass, gs, shoot nutrient concentrations and mycorrhizal colonization were measured in all accessions, and Lo and gene expression in five accessions. The diverse accessions varied in physiology and gene expression; some accessions were also larger or had higher gs when colonized by F. mosseae. In the five accessions, Lo was higher in two accessions when colonized by AMF and also maintained within a much smaller range than the mock-inoculated plants. Expression of MtPIP1 correlated with both gs and Lo, and when plants were more than 3% colonized, mycorrhizal colonization correlated with Lo. Accession and AMF treatments had profound effects on M. truncatula, including several measures of plant water relations. Correlations between response variables, especially between molecular and physiological variables, across genotypes, highlight the findings of this study.