Data from: Fungal effects on plant-plant interactions contribute to grassland plant abundances: evidence from the field

1. Plant-fungal interactions can have strong effects on plant abundances,
both through direct effects on plant performance and indirect effects on
competition and facilitation. Most evidence linking fungi to plant
abundances derives from direct fungal effects on initial growth, with
little evidence linking fungal effects on plant-plant interactions in
intact communities to plant abundances for any plant life history stage.
2. We transplanted 4320 individuals belonging to 18 plant species into
plots where we removed neighbouring vegetation and suppressed fungi using
fungicide in a factorial design. We monitored plant survival and growth
for three years, using this data to test whether fungi had net effects on
how plant-plant interactions affected different plant life history
components (initial survival/growth, adult survival/growth). We then
tested whether these indirect fungal effects or direct fungal effects on
plant performance best explained plant commonness (frequency of
occurrence) and local density (percent cover). Finally, we measured
differences in root-associated fungi following fungal suppression and
associated these differences with fungal effects on plant performance. 3.
Overall, fungi increased competitive effects on survival (i.e. lower
survival with fungi intact), but reduced competitive effects on growth of
adult plants (i.e. higher growth when fungi intact). Among the focal
species, these indirect fungal effects increased survival for more common
species relative to rarer species. However, indirect fungal effects on
adult growth benefitted rarer species more than common species. Local
plant densities were unassociated with indirect fungal effects, but were
negatively associated with direct fungal effects on survival and adult
growth. This suggests that fungi limit local dominance, thereby indirectly
increasing the establishment of common species and the growth of rare
species. 4. Synthesis. By using a variety of plant species and suppressing
both fungi and neighbours, we show that fungi have net indirect effects,
through plant-plant interactions, within intact plant communities.
Variation among species in both direct and indirect fungal effects
contributed to plant abundances, yet fungal effects did not consistently
benefit either common or rare species. However, regardless of commonness,
fungi directly reduced growth and survival for species with high local
densities, consistent with plant-soil feedbacks limiting species
dominance.