Effects on plot scale fluxes via changes in plant biomass
This work suggests that the increase in plant biomass with plant diversity directly increased ecosystem rates of carbon uptake and release. In particular, increasing plant diversity from 1 to 16 species nearly doubled both carbon uptake (GPP) and ecosystem respiration (Re), mirroring the increase in total plant biomass with plant diversity in this experiment (Reich et al. 2012). After accounting for the increase in plant biomass, carbon fluxes remained constant across the gradient of plant diversity. Thus, in the experimental grassland communities at Cedar Creek, standing plant biomass is a good predictor of ecosystem carbon fluxes (see Fig. 1). Our findings are supported by those of Stocker et al. (1999), who reported a linear relationship between the increase in plant biomass and in ecosystem carbon fluxes with increasing plant diversity.
Path analyses suggest that changes in plant biomass in response to heterotroph removal did not contribute significantly to changes in carbon fluxes in this study. Compared to previous studies from this and other experiments at Cedar Creek that have shown that foliar fungi and arthropods strongly suppress plant biomass in these prairies (Mitchell 2003; Seabloom et al. 2017; Kohli et al. 2019), we found that foliar fungi had weakly significant effect and arthropods had no effect on plant biomass in our plots. Perhaps this is because, unlike these multi-year studies, we examined fluxes and biomass in only a subset of the experimental plots and only in a single study year. Thus, it is likely that the overall effects of heterotrophs on instantaneous carbon fluxes reported here underestimate the long-term effects.