Evolution of phytolith deposition in modern bryophytes, and implications for the fossil record and influence on silica cycle in early land plant evolution

Abstract

Summary Anecdotal evidence indicating substantial silica accumulation in tissues of bryophytes suggests that silica (phytolith) deposition evolved early on in embryophytes. To test this hypothesis, we conducted the first survey of phytolith content representing the major liverwort, moss and hornwort clades. We also assessed the diagnostic value of bryophyte phytoliths. Silica extracted from bryophyte material through wet‐ashing was described, focusing on abundance, classifying taxa as nonproducers, light producers and higher producers; and phytolith morphotypes. Ancestral state reconstruction of these characters was performed for mosses and liverworts using published phylogenies. Phytoliths are present in multiple subclades within liverworts, mosses and hornworts, but these phyla were not ancestrally high silica‐producers. Higher deposition occurs in liverworts and mosses with specialized water‐conducting cells. We hypothesize that active, high silica accumulation was not ancestral for embryophytes, but became possible in clades with increased water conductance. Phytoliths of diagnostic structures (e.g. pegged rhizoids) could help track bryophyte clades or water conductance evolution in the fossil record.

Silicon in the Soil–Plant Continuum: Intricate Feedback Mechanisms within Ecosystems

“…The occurrence of high Si contents in a single subfamily of orchids (one of the largest plant families globally) is not unique: 29 of the 412 angiosperm families include both Si-rich and Si-poor species (7% of all angiosperm families, but 17% of families for which data exist) [23]. Finally, it should be noted that although most research revolves around seed plants, silicon and phytoliths are common and abundant in many bryophytes and pteridophytes [122,172,[176][177][178] (phytolith-like "mycoliths" also occur in fungi [179]), sometimes in contents that surpass those found in Poaceae species [172].…”

“…This variability is by far the one that is best documented and analyzed [197,[215][216][217][218][219], in part because of its usefulness in palaeoecology and archaeology [131][132][133]174,[208][209][210]216,[220][221][222][223][224][225][226][227][228][229][230]. Of no less importance, but less developed is the potential of using morphotypical analyses in studying plant evolutionary history, owing to the correspondence of some morphotypes to phylogeny and thus the ability to identify plant taxa ancestors using putative ancestral morphotypes [176,195,[231][232][233].…”

The Relative Importance of Cell Wall and Lumen Phytoliths in Carbon Sequestration in Soil: A Hypothesis

“…I have included a few examples of work on silica deposition in non-grass species in Tables 2, 3: nettle, Equisetum, Cannabis, white spruce, and bracken. Recently, phytolith production in the bryophytes has also been investigated (Thummel et al, 2018), and most silica deposition seems to be in the cell walls of these plants. It seems that there is little epidermal lumen deposition outside the grasses.…”

Evapotranspiration‐linked silica deposition in a basal tracheophyte plant (Lycopodiaceae: Lycopodiella alopecuroides): implications for the evolutionary origins of phytoliths

“…The tapering overall shape of the apex aggregate and its recognizable elongate, guard cell, and vascular components lend it a unique morphology dissimilar from phytoliths of previously described plant taxa (Piperno, 2006). One of the few potential sources of confusion is the phyllid apex phytoliths of bryophytes (APX_CLU), but these can be readily distinguished from L. alopecuroides aggregates by their lack of vascular constituent phytoliths (TRA_ANN), the feature which lends APX_TRA nomen nov. its name (Thummel et al, 2019). Poaceaen silicified hair cells may also present potential confusion with APX_TRA nomen nov. but may be differentiated by their significantly smaller size, lack of surficial guard cells, and much When disaggregated, the constituent morphotypes of the microphyll apex may still be identified if found in close association.…”

“…Although present to a limited degree even in algae, phytoliths first arise significantly in conjunction with the development of terrestriality, appearing in the earliest‐diverging land plants like bryophytes and hornworts as thin, light silicifications of epidermal cells (Golokhvast et al ., 2014; Thummel et al ., 2019). The later development of vascular systems in tracheophytes led to more complex silicification patterns and greater phytolith deposition (Thummel et al ., 2019). Indeed, silicification occurs across all major tracheophyte clades to at least some degree, reaching notable maxima in the ‘scouring rush’ monilophyte genus Equisetum and angiosperm monocot grasses (Katz, 2015).…”