Phyllosphere microbes decouple nutrient enrichment from plant productivity

This decoupling was not explained by direct microbial competition for nutrients or predicted microbial functions associated with pathogenicity, oxygen depletion, or acidification. Instead, nutrient enrichment stimulated biofilm formation, potentially restricting plant access to nutrients. Predicted microbial phosphorus immobilization and transformation also increased, but neither explained the decline in ecosystem phosphorus removal.

This decline instead reflected lower plant productivity associated with biofilm formation, leaving much of the phosphorus unused. These patterns were consistent across ploidy levels, with the productivity advantage of polyploids associated with greater nutrient-use efficiency rather than greater tolerance of microbial effects. Our results reveal that phyllosphere microbiomes mediate how nutrient enrichment translates into ecosystem functioning.