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.