Abstract
Plant-associated microbes play a key role in mediating the relationship
between plant diversity and productivity. However, previous studies have
generally focused on a sole microbial guild (i.e. plant-beneficial
microbes or pathogens), and on either aboveground or belowground
microbes. As a result, the interplay among different microbial guilds
and the overall impact of above- and belowground microbes on plant
diversity-productivity relationships have rarely been investigated. Here
we carried out an experiment where we applied microbial inocula
collected from leaves and soils in the field onto plant leaves and soil
in a greenhouse experiment with a herbaceous plant community. We showed
that microbial inoculation of leaves reduced plant productivity and this
negative effect was weaker at higher plant diversity, which promoted
positive diversity-productivity relationships through complementarity
effects. In contrast, microbial inoculation of soil alone had no impact
on plant diversity-productivity relationships, but it counteracted the
negative effects of leaf inoculum on plant productivity and weakened the
leaf microbe-induced positive diversity-productivity relationships. We
found that the abundance of arbuscular mycorrhizal fungi andStreptomyces bacteria increased when soil microbes were
inoculated, and such increase was more significant at lower plant
diversity, potentially explaining the effects of soil inoculation on
plant productivity. These results suggest that the belowground plant
beneficial microbes can counteract the effect of aboveground plant
pathogens in mediating positive plant diversity-productivity
relationships. Simultaneous study of plant-pathogenic and -beneficial
microbes both above- and belowground is required to better understand
the contributions of plant-associated microbes to biodiversity-ecosystem
function relationships.