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Lalica, Madison [1], Tomescu, Alexandru [2].

Glomeromycete spores associated with early tracheophytes in the Lower Devonian (Emsian; c. 400 ma) of Gaspé (Quebec, Canada).

Fossil assemblages preserved in fluvial-coastal Emsian strata of the Battery Point Formation of Gaspé Bay (Quebec, Canada) are among the most diverse occurrences of Early Devonian permineralized plants worldwide. The plants host fungal material, including spores that show affinities to the Glomeromycotina. A survey of over 200 specimens within 12 trimerophyte axes, reveals the presence of two spore size categories. Spores in the small category (40-65 μm) occur in a single axis and exhibit few informative features. Nevertheless, they show two distinct unornamented wall layers and evidence of subtending hyphae, both of which are characteristic of glomoid glomeromycete spores. The most frequently occurring type is the large spores (90-240 μm) that may represent a new species of Glomites. These spores exhibit four wall layers (when well preserved), of which two are more resilient: a thick, dark layer to the outside of a thin, membranous layer. The spores are globose to ovoid and have subtending hyphae with varying types of occlusion. Taphonomic factors or biotic interactions may distort their shapes: some spores display crater-like depressions of consistent morphology possibly produced in reaction to organisms attempting to penetrate the spores; others contain minute structures reflecting putative fungal-fungal interactions. Several lines of circumstantial evidence suggest that the spores were metabolically active within their plant hosts at the time of fossilization and that the plants were alive at the time of infection: hyphae and vesicles, indicative of metabolically active fungi co-occur with the spores; when well preserved, the tissues of some host plant axes are notably affected in the vicinity of the spores; within individual axes, spores show varying levels of preservation, consistent with continued spore development (and subsequent breakdown), which implies longer-term interactions that are more likely sustained in living plant tissues. In light of comparisons with other fossil glomeromycetes and considering the life history traits of living glomeromycetes, our observations of the Battery Point Formation material suggest that the fungi producing the spores had an endomycorrhizal role. This occurrence is one of very few reports of fungal and microbial life in the Battery Point Formation. These fungal fossils represent the only Early Devonian glomeromycete occurrence documented outside the hot spring deposits of the Rhynie chert. The presence of glomeromycetes in plants of typical fluvial-coastal environments and their putative mycorrhizal role, suggest that like their extant counterparts, glomeromycetes were relatively ubiquitous symbionts of tracheophytes, by the Early Devonian.

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1 - Humboldt State University, Department of Biological Sciences, Arcata, CA, 95521, USA
2 - Humboldt State University, Department Of Biological Sciences, 1 Harpst Street, Arcata, CA, 95521, United States

plant-fungal interactions.

Presentation Type: Oral Paper
Session: PL4, Paleobotany: Honoring Fran Hueber - Session II
Location: /
Date: Tuesday, July 20th, 2021
Time: 12:30 PM(EDT)
Number: PL4001
Abstract ID:80
Candidate for Awards:Isabel Cookson Award,Maynard F. Moseley Award

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