Abstract
Much recent work has focused on characterising the mutualistic elements
of the plant microbiome, often aiming to identify bacterial strains that
can increase plant fitness. Although most work has focused on
terrestrial plants, Lemna minor , a floating aquatic angiosperm,
is increasingly used as a model in host-microbe interactions. Here we
assess the fitness and phenotypic consequences of the full microbiome
for L. minor by assaying plants from eight natural sites, with
and without their microbiomes, over a range of environmental conditions.
We find that the microbiome supresses plant fitness, for all genotypes
and across all environmental conditions. This decrease in fitness was
accompanied by phenotypic changes, with plants forming smaller colonies
and producing smaller fronds and shorter roots with the microbiome
present. Although the L. minor microbiome clearly includes
important symbionts, our findings suggest that we cannot discount the
important pathogenic, parasitic, and competitive interactions, whose
influence can override that of mutualists.