Fungal symbiont effects on dune plant diversity depend on precipitation

Abstract

Summary1. 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 rainout shelters and rainfall additions. We monitored natural rates of colonization by new plant individuals over 3 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.

Plant–fungal symbiosis affects litter decomposition during primary succession

“…Additionally, our precipitation manipulation led to an average of 9% higher moisture in augmented plots compared to reduced plots at both 20 and 40 cm depth (Supplementary material Appendix 1 Table A1, Fig. A1, Rudgers et al ).…”

“…isolates cultured from A. breviligulata into the meristem of each seedling (E+ treatment) and sham‐inoculated other seedlings (E– treatment) (Leuchtmann and Clay ). This inoculation method had an 8% success rate (Emery et al , Rudgers et al ) similar to Epichloë inoculation of other grass species (Chung et al ). Only successfully inoculated genotypes were used for our E+ treatment.…”

“…Only successfully inoculated genotypes were used for our E+ treatment. Plant responses from the field experiment for 2010–2013 were presented by Emery et al () and Rudgers et al (). Here, we counted the number of A. breviligulata tillers per plot on 27 May 2015 to estimate above‐ground plant biomass using allometric equations.…”

“…Under the highest CO 2 emission scenarios, general circulation models project that this region will experience a 5°C increase in mean annual temperature by 2070–2099 (Hayhoe et al ). Furthermore, downscaled predictions from the IPCC Fourth Assessment (IPCC ) vary from + 19% to –31% change in growing season precipitation (Rudgers et al ) while IPCC Fifth Assesement ensemble model predicts a 10–25% increase in annual preciptiation for the region (IPCC ).…”

Identification of the fungal endophyte of Ammophila breviligulata (American beachgrass) as Epichloë amarillans

“…A. breviligulata is ecologically important in shoreline dune building. Endophyte infected A. breviligulata was reported to exhibit greater vegetative growth and dune building relative to uninfected plants ( Emery, Bell-Dereske & Rudgers, 2015 ) but was also correlated with reduced species richness at the field site ( Rudgers et al, 2015 ). In these reports the endophyte was referred to as Epichloë sp.…”