Presence of microbiome decreases fitness and modifies phenotype in the aquatic plant Lemna minor

Plants live in close association with microbial organisms that inhabit the environment in which they grow. Much recent work has aimed to characterize these plant-microbiome interactions, identifying those associations that increase growth. Although most work has focused on terrestrial plants, Lemna minor, a floating aquatic angiosperm, is increasingly used as a model in host-microbe interactions and many bacterial associations have been shown to play an important role in supporting plant fitness. However, the ubiquity and stability of these interactions as well as their dependence on specific abiotic environmental conditions remain unclear. Here, we assess the impact of a full L. minor microbiome on plant fitness and phenotype by assaying plants from eight natural sites, with and without their microbiomes, over a range of abiotic environmental conditions. We find that the microbiome systematically suppressed plant fitness, although the magnitude of this effect varied among plant genotypes and depended on the abiotic environment. Presence of the microbiome also resulted in phenotypic changes, with plants forming smaller colonies and producing smaller fronds and shorter roots. Differences in phenotype among plant genotypes were reduced when the microbiome was removed, as were genotype by environment interactions, suggesting that the microbiome plays a role in mediating the plant phenotypic response to the environment. It is known that the plant microbiome influences its hosts, but that, depending on the context and the plant, the effect can either increase or decrease host performance. We found that for the small and free-floating aquatic plant Lemna minor , its microbiome reduced growth rate and changed the phenotype of the plant. These effects were consistent for several plant genotypes and only moderately depended on the context, specifically light and nutrient availability. Removing the microbiome homogenized plant phenotypes and influenced how the L. minor populations responded to the abiotic environment. This suggests that the microbiome at least, in part, mediates the plant's response to the environment.

Automated summary

Plants have close associations with microbial organisms, which can either increase or decrease plant performance depending on the context and the plant species. This study focused on the microbiome of the floating aquatic plant Lemna minor and found that it decreased plant fitness and altered plant phenotype. These effects were consistent across different plant genotypes and moderately influenced by the abiotic environment.