Discussion
Our study demonstrates a key role of biotic interactions, particularly between plants and foliar fungi, in ecosystem carbon flux rates. The effects of plant diversity were driven primarily by changes in plant biomass, whereas effects of foliar fungi were driven by a combination of changes in plant biomass, plant community composition and foliar chemistry. In support of H1 , declining plant diversity reduced GPP and Re, because of the lower plant biomass in low diversity communities. In contrast, in partial support of H2 andH3 , removal of foliar fungi increased carbon fluxes, because of both an increase in plant biomass and in mass-specific rates of GPP, Re and NEE. Removal of foliar fungi increased the relative abundance of N rich leguminous forbs and suppressed C4 grasses, increasing community wide foliar N content and thereby mass specific flux rates. Contrary to our (H3 ) expectations, removal of arthropods and soil fungi did not significantly impact instantaneous carbon fluxes. Effects of foliar fungi were mediated by plant and heterotroph community context, in support of H4 – e.g., the impacts of foliar fungi were strongest in low diversity plant communities when arthropods and soil fungi were present (i.e. not experimentally removed).