Microbial symbionts have had an instrumental role in the trajectory of terrestrial ecosystems, facilitating land plant colonization and conferring adaptive advantages that allow plant survival under harsh environmental conditions. Interactions with arbuscular mycorrhizal fungi, for example, are widespread among land plants — characterized by the exchange of nutrients for plant carbohydrates as well as conferring resistance to various stresses. Recent studies suggest, however, that climate change may disrupt these beneficial interactions with cascading effects through ecosystems. Writing in Global Change Biology, Joshua Fowler and colleagues from Rice University, USA, take a closer look at how plant–microbial mutualisms have changed over the past 200 years.
By examining herbarium samples of three host grasses distributed across North America, Fowler et al. were able to estimate the changing prevalence of Epichloë fungal endophytes since 1824. Seed-transmitted Epichloë form specific mutualisms with cool-season grasses, which are beneficial to plants owing to the fungal production of bioactive alkaloids that confer protection against herbivory. This study found that, since 1824, prevalence of fungal symbionts has increased by as much as 50%. Although these changes were associated with seasonal climatic changes, responses exhibited context and species specificity. Increasing precipitation during the peak growing season was associated with increased endophyte prevalence in two Agrostis species, whereas in Elymus virginicus increasing prevalence was associated with reductions in rainfall.
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