Abstract Detail



Paleobotany

Thummel, Ryan [1], Brightly, William [2], Stromberg, Caroline [3].

Evolution of phytolith deposition in modern bryophytes and implications for the fossil record and influence on silica cycle of early land plants.

        Anecdotal evidence suggests that bryophytes accumulate substantial silica in their tissues, supporting the hypothesis that silica (phytolith) deposition evolved early in land plants. To test this hypothesis, we conducted the first survey of phytolith content in bryophytes comprising 135 specimens representing the major liverwort-, moss-, and hornwort clades. We also evaluated bryophyte phytolith shapes to assess their potential for establishing an alternative fossil record of non-vascular plants. Silica extracted from bryophyte material through wet-ashing was described in terms of (a) silica content, classifying taxa as non-producers, rare-, and higher producers; and (b) phytolith morphotypes. Ancestral state reconstruction of these characters was performed for mosses and liverworts using published phylogenies. Although phytoliths are present in multiple subclades within liverworts, mosses or hornworts, these phyla were not ancestrally high silica-producers, although ancestral rare deposition is possible. Thus, bryophytes did not significantly impact the silica cycle in early terrestrial ecosystems. Higher deposition was only observed in liverwort and moss clades with specialized water conducting cells. Given this, we hypothesize that water conductance may influence the level of phytolith deposition in bryophytes, and possibly land plants as a whole. If higher deposition was not ancestral in the bryophytes but restricted to bryophytes and other land plants with well-developed water conductance, it is likely that the earliest non-vascular land plants did not significantly contribute to the silica cycle. However, our analysis and the observed, rare phytoliths in bryophytes without well-developed water conductance suggests that a phytolith record could nevertheless exist for the earliest land plants, under the appropriate taphonomic conditions. In particular, the widespread occurrence of phytoliths of water conducting cells in bryophytes and tracheophytes suggests that phytoliths could provide a valuable record of the evolution and diversification of water conducting cells in land plants. In addition, phytoliths of diagnostic structures (e.g., pegged rhizoids) could help track specific bryophyte clades in the fossil record.


1 - University of Washington, Department of Biology, University of Washington, Box 351800, 24 Kincaid Hall, Seattle, Washington, 98195, United States
2 - 2208 NW 64th St, Seattle, WA, 98107, United States
3 - University Of Washington, Department Of Biology, 24 Kincaid Hall, Box 351800, Seattle, WA, 98195, United States

Keywords:
phytolith
bryophyte
silica cycle
early land plants.

Presentation Type: Oral Paper
Number: 0002
Abstract ID:540
Candidate for Awards:None


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