Abstract
Symbiotic associations can be disrupted by disturbance or by changing environmental conditions. Endophytes are fungal and bacterial symbionts of plants that can affect performance. As in more widely known symbioses, acute or chronic stressor exposure might trigger disassociation of endophytes from host plants. We tested this hypothesis by examining the effects of oil exposure following the Deepwater Horizon (DWH) oil spill on endophyte diversity and abundance in Spartina alterniflora – the foundational plant in northern Gulf coast salt marshes affected by the spill. We compared bacterial and fungal endophytes isolated from plants in reference areas to isolates from plants collected in areas with residual oil that has persisted for more than three years after the DWH spill. DNA sequence-based estimates showed that oil exposure shifted endophyte diversity and community structure. Plants from oiled areas exhibited near total loss of leaf fungal endophytes. Root fungal endophytes exhibited a more modest decline and little change was observed in endophytic bacterial diversity or abundance, though a shift towards hydrocarbon metabolizers was found in plants from oiled sites. These results show that plant-endophyte symbioses can be disrupted by stressor exposure, and indicate that symbiont community disassembly in marsh plants is an enduring outcome of the DWH spill.
Highlights
Disturbance or shifts in environmental conditions can disrupt widespread and often obligate symbiotic associations
Fungal endophyte diversity was significantly lower in leaves (p
Our findings indicate that stressor exposure can result in sustained loss of endophytes in a system where elevated vulnerability of plant hosts could cascade into functional deficits that reshape whole ecosystems
Summary
Disturbance or shifts in environmental conditions can disrupt widespread and often obligate symbiotic associations. Many symbionts confer benefits to hosts, such as nutrient acquisition (e.g., mycorrhizae and nitrogen-fixing bacteria), protection through production of toxins (e.g., cyanobacteria in cycads), and production of photosynthate (e.g., algae in lichens and zooxanthellae in corals). These relationships are often beneficial to both partners, changes in environmental conditions, such as those brought on by climate change or acute disturbances, PLOS ONE | DOI:10.1371/journal.pone.0122378. Endophyte Responses to Oil Exposure collection and analysis, decision to publish, or preparation of the manuscript These relationships are often beneficial to both partners, changes in environmental conditions, such as those brought on by climate change or acute disturbances, PLOS ONE | DOI:10.1371/journal.pone.0122378 April 29, 2015
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