Effects of plant diversity and heterotroph removal on total plot
level C fluxes
As plant diversity increased from 1 to 16 species in control plots,i.e. in the presence of all heterotrophs, NEE increased from an
average of 3.95 (±0.96) in monocultures to 6.9 (±1.36) μ mol
CO2 m-2 s-1 in 16
species plots, but this trend was not statistically significant (Table
S2, Fig. 2C). Mean GPP and Re roughly doubled along this
gradient of plant diversity (Tables S3-S4, Figs. 2A, B). GPP increased
from 8.37 (±1.06) μ mol CO2 m-2s-1 (mean ± 1 s.e.) in monocultures to 16.18 (±2.03)
in the 16-species plots, and Re increased from 4.42
(±0.36) in monocultures to 9.28 (±1.88) μ mol CO2m-2 s-1 in the high diversity plots.
Thus, the increase in GPP with plant diversity was offset by the
increase in Re such that there was no significant effect
of plant diversity on NEE.
Removal of all heterotrophs simultaneously did not affect NEE, GPP or
Re (Tables S2-S4, Fig. 2). Among all heterotrophs, only
foliar fungi influenced carbon fluxes when removed independently.
Removal of foliar fungi increased GPP by an average of 54% at each
plant diversity level (Table S3, Fig 2A). Because GPP increased with
plant diversity (as noted above), the absolute change in GPP due to
removal of foliar fungi was greatest in monocultures and declined with
increasing plant diversity. Heterotroph removal did not significantly
influence Re (Table S4, Fig. 2B). Thus, plots where
foliar fungi had been removed had greater net carbon uptake: compared to
the control plots, NEE increased by 45% in the subplots where foliar
fungi were removed and this effect was strongest in low diversity
communities (Table S3, Fig. 2C). Foliar fungi only impacted total fluxes
when all other consumer groups were present; total fluxes in treatment
and control plots were the same when arthropods and soil fungi were
removed in addition to foliar-fungi, demonstrating that plant-foliar
fungal interactions determining carbon flux rates depended the
heterotroph foodweb context (Tables S2-S4; Fig. 2).