DOI: 10.5061/dryad.17jr3
title: Data from: Fungal symbiont effects on dune plant diversity depend on precipitation

description: 1. Historically, mutualisms have been considered to be less important than
 antagonisms in affecting the composition of ecological communities. In
 plant communities, beneficial microbes may feature as keystone mutualists
 in structuring community composition. Understanding the direction and
 magnitude of mutualist effects at the community scale may be critical for
 making accurate predictions on plant responses to climate change,
 particularly for mutualists that ameliorate climate-induced stressors.
 Such mitigation could shift outcomes between mutualist-enhanced species
 diversity and mutualist-reduced diversity, depending on whether a
 mutualist accelerates habitat modification or competitive exclusion by its
 partner species. 2. Here, we tested the relative importance and
 interactive effects of altered precipitation and symbiosis between an
 epichloid fungal endophyte and a dominant grass species for dune plant
 communities along the Great Lakes, USA. In 2010, we imposed field
 manipulations of endophyte presence in the foundation dune grass Ammophila
 breviligulata in combination with rain-out shelters and rainfall
 additions. We monitored natural rates of colonization by new plant
 individuals over three years. 3. Under the current precipitation regime,
 endophyte symbiosis in A. breviligulata reduced colonizing plant
 diversity, species richness, and evenness. This effect depended on the
 amount of precipitation, with the symbiosis having weaker effects on plant
 diversity under both augmented and reduced rainfall treatments. 4. Despite
 the overall negative effect of endophyte symbiosis on plant diversity,
 plant responses to the endophyte were species-specific. A federally
 threatened forb, Cirsium pitcheri, increased in abundance when the
 symbiosis was present, regardless of precipitation regime. Endophyte
 symbiosis in A. breviligulata caused minor reductions in the abundance of
 other grass species; however, augmented precipitation benefited other
 grasses. 5. Synthesis. We show that microbial mutualisms can have strong
 effects on community structure in a native ecosystem and that the amount
 of precipitation has the potential to alter how these keystone species
 interactions affect community composition. Predictions on future plant
 community structure, for both restored and native dunes, can be improved
 by accounting for the presence of fungal symbionts in the foundation plant
 species.
description: VWCData were collected in
 the field experiment using a hand-held soil moisture meter (Aquaterr M
 300, Costa Mesa, CA) with measurements of volumetric water content taken
 at 20 cm and 40 cm soil depths. Plot=unique plot number, row=position of
 plot in the experimental matrix, col=column position of plot in the
 experimental matrix, EF=endophyte presence(1) or absence(0),
 Water=reduced(L), ambient(M), or augmented(H), Date=date of observation,
 VWC20=mean volumetric water content per plot at 20 cm soil depth,
 VWC40=mean volumetric water content per plot at 40 cm soil
 depth.Plant Community
 Diversity and Abundance dataPlantCommunity.xlsxperMANOVA2012 - plant species data matrix for 2012perMANOVA2012.xlsxperMANOVA2013 - Plant species data matrix for 2013perMANOVA2013.xlsx