Ecophysiological Constraints on Spore Establishment in Bryophytes

1. Many threatened bryophytes are restricted to patchy and temporary substrates such as dead wood and tree stems. Their persistence depends on successful colonizations of new patches. Spore germination may then be limited by substrate quality and wetness. 2. In vitro experiments were used to test the effects of pH and moisture on the establishment of spores of the moss species Neckera pennata Hedw. and Buxbaumia viridis (DC) Moug. & Nestl. 3. Low pH and water potential prolonged the lag phase preceding germination and reduced final germination. The interaction between pH and moisture suggests that high water availability facilitates germination at suboptimal pH, and vice versa. 4. The results reflect the species' habitats: the wood-inhabiting B. viridis had higher capacity to germinate at low pH, while spores of the epiphyte N. pennata showed earlier germination at low water potential and survived longer in a dry state. This supports the notion that bryophytes are most strongly affected by substrate quality during establishment. 5. We suggest that a trade-off exists among moss spores between the ability to colonize substrates with low moisture-holding capacity and low pH, and that the positive effect of high pH is largely that it speeds up germination thereby enabling the spores to exploit short, moist periods.