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).