Mycorrhizal inoculation mitigates damage from an intermediate, but not severe, frost event for a cool-season perennial bunchgrass

Abstract

Extreme cold events can damage plant tissues, altering growth and reproduction. Soil fungi may help plants tolerate environmental stressors, but the role these microbes play during episodes of severe cold warrants further examination. Using the bunchgrass Elymus canadensis, we tested how inoculation with mycorrhizal fungi alters plant tolerance to freezing temperatures (tested at -8C and -16C). We found that, regardless of mycorrhizal inoculation, E. canadensis exposed to -16C exhibited greater tissue damage, less tiller growth, and fewer reproductive tillers than plants exposed to control or -8C conditions. Plants exposed to -8C and -16C displayed greater levels of visible damage compared to control plants. Mycorrhizae reduced damaged on tillers in the -8C treatment, but had less effect on tiller damage in control or -16C treatments. Inoculation with AM fungi limited E. canadensis tiller number, but only at the control temperature, suggesting mycorrhizae may impose costs on E. canadensis under benign thermal conditions. Our study demonstrates that extreme temperatures can affect multiple components of E. canadensis growth, and that costs and benefits of AM fungi, where found, depend upon the thermal environment. Our findings reinforce the overarching importance of historically rare, but increasingly common, environmental extremes in shaping the growth of plants.