Conclusions
Our study underscores the importance of considering the effects of
biotic interactions, especially between plants and foliar fungi, on
ecosystem carbon fluxes in addition to carbon stocks (e.g., plant
biomass). Together with previous studies, our results suggest that these
interactions influence carbon fluxes by a combination of effects ranging
from leaf to community scale (Mitchell 2003; Borer et al. 2015; Seabloom
et al. 2017). Foliar fungal endophytes and pathogens colonize the leaves
of all plants (Rodriguez et al. 2009; Dobson & Crawley 1994); examining
whether the large effects of foliar fungi reported here are ubiquitous
across biomes and ecosystems will shed light on the generality of our
findings. The role of foliar fungi is likely to become even more
important in the future with climatic changes (Harvell et al. 2002;
Olofsson et al. 2011) and loss of plant diversity (Mitchell et al. 2002,
Civitello et al. 2015), especially since we found that foliar fungi
acted differently on carbon fluxes in low vs high plant diversity
communities: they suppressed mass-specific flux rates in low diversity
communities, but suppressed plant biomass in high diversity communities.
These results further suggest that integrating plant disease ecology
into global change and ecosystem ecology will be a fruitful avenue for
additional research into human alterations of carbon cycling (Preston et
al. 2016), as foliar fungi have large but largely unquantified effects
on ecosystem flux rates.