Experimental studies of epixylic bryophytes require stable, biologically inactive substrata with physical properties that mimic those of coarse decayed wood. In two preliminary tests, we compared three synthetic logs (made from upholstery wadding, mattress foam, and floral foam) to decayed natural logs, in terms of their physical properties, moisture transmission, and ability to support growth of Dicranum flagellare in the laboratory. We also tested the effects of clumped vs. smeared propagule application on growth response. Vegetative moss propagules (flagellae and dried gametophore fragments) were applied as clumps or smears with nutrient agar gel, and evaluated as to horizontal expansion, vertical growth and dry weight of new growth over 6 months. Synthetic logs had higher porosity and lower density than natural logs, but showed similar moisture transmission capabilities to each other and to natural logs when moisture was supplied from the base. Nevertheless, surficial water potentials were consistently less than -5 MPa, and were therefore incapable of supporting bryophyte growth without applying liquid water from above. Horizontal expansion of D. flagellare was greatest with a smear application on floral foam logs, but vertical growth was greatest on upholstery wadding logs with a clumped application. Although floral foam (substratum) and smear (application) produced the greatest new shoot growth, observations suggest that the moss may allocate more growth to rhizoids on more penetrable substrata (those with a larger mean pore size). Future studies must modify the structure of synthetic substrate units to more closely mimic the moisture-related characteristics of rotting wood of target species, and further isolate the components of bryophyte growth.
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Vol. 32 • No. 4