Arbuscular mycorrhizae reduce stress-induced plasticity of plant functional traits. A meta-analysis study

We aimed at exploring the plant functional traits whose stress-induced plasticity is altered by the presence of AM fungi, considering the direction of their changes. We also sought for a coordinated variation of plant biomass and functional traits, during plant adaptation to environmental stressors, and the role of AM status on the variation. We performed a meta-analysis across 114 articles spanning 110 plant species or cultivars. We quantified the size effect of AM symbiosis on the stress-induced plasticity of several reported and calculated functional traits, and using linear mixed model analysis (LMM). Correlation between traits plasticity and total biomass variation were also performed through LMM. The literature search and further selection yielded seven functional traits, extracted from 114 laboratory studies, including 888 observations and 110 plant species/cultivars. Evidence for significant effects of predictor variables (type of stress, AM symbiosis and/or their interaction) on plasticity were found for three of these functional traits: leaf-area ratio (LAR), root mass fraction (RMF) and root-shoot (R:S) ratio. Our results provided evidence to accept the hypothesis that AM fungal inoculation may reduce the phenotypic plasticity of important plant functional traits leaf area ratio (LAR), root mass fraction (RMF) and root-shoot (R:S) ratio, by decreasing its magnitude. We also found a weak correlation between traits plasticity and total biomass variation. Although our literature search and data collection were intensive and our results robust, the scope of our conclusions is limited by the agronomical bias of plant species targeted by the meta-analysis. Further knowledge on non-cultivable plant species and better understanding of the mechanisms ruling resources allocation in plants would allow more generalized conclusions.