Dry/wet cycling reduces spore germination and viability in six peatland bryophytes

Dry/wet cycling driven by water level fluctuation in wetlands may strongly influence the destiny of seeds. However, how dry/wet cycling affects spore survival and germinability in peatland bryophytes is poorly known. Six peatland bryophytes, including three hummock and three hollow dwelling Sphagnum species, were chosen as study species. We tested the effects of dry (60 % air RH)/wet (waterlogged) cycling frequency (once per 12, 8 and 4 d for low, medium and high, respectively) and ratio (3:1, 1:1 and 1:3, regarding time in dry:wet per cycle) on spore germinability, viability, dormancy percentage and protonema development. Dry/wet cycling significantly reduced spore germination percentage, viability and slowed protonema development in all species, being more pronounced with higher dry/wet cycling frequencies. The hummock species S. capillifolium and S. fuscum had a higher spore germination percentage after the continuously dry treatment, while the hollow species S. angustifolium, S. squarrosum and S. subsecundum showed an opposite response, as compared to the continuously wet treatment. Except for S. squarrosum, spore viability was higher after the dry treatment than after the wet treatment. Spore viability and dormancy percentage were higher after a dry/wet ratio of 1:3 than after 3:1 and 1:1. Our study shows that germinability and viability of bryophyte spores are reduced by dry/wet cycling (especially when frequent) in peatlands. This emphasizes the necessity to ensure constant water levels and low frequencies of water level fluctuations, which are relevant in connection with wetland restorations, to promote Sphagnum spore survival and establishment in peatlands after disturbances.