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

Abstract

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 understood.• Six peatland bryophytes, three hummock-and three hollow-dwelling Sphagnum species, were chosen as study species. We tested the effects of dry (60% air RH)/wet (waterlogging) cycle frequency (once per 12, 8 or 4 days for low, medium or high, respectively) and ratio (3:1, 1:1 or 1:3 dry:wet time per cycle) on spore germinability, viability, dormancy percentage and protonema development.• Dry/wet cycling significantly reduced spore germination percentage and viability and slowed protonema development in all Sphagnum species, being more pronounced with higher dry/wet cycling frequencies. The hummock species S. capillifolium and S. fuscum had higher spore germination percentage after the continuous dry treatment, while the hollow species S. angustifolium, S. squarrosum and S. subsecundum showed the opposite response, compared to the continuously wet treatment. Except for S. squarrosum, spore viability was higher after the dry than after the wet treatment. Spore viability and dormancy percentage were higher after a dry/wet ratio of 1:3 than after ratios of 3:1 and 1:1.• Our study shows that both germinability and viability of bryophyte spores are reduced by dry/wet cycling (especially when frequent) in peatlands. This emphasizes the need to ensure constant water levels and low frequencies of water level fluctuation, which are relevant in connection with wetland restoration, to promote Sphagnum spore survival and establishment in peatlands after disturbances.

Seed dormancy types and germination response of 15 plant species in temperate montane peatlands

“…These findings suggest that differences in dormancy are also associated with environmental change. For example, water table fluctuation may affect spore germinationability (Feng et al., 2017 ; Bu et al., 2017 ) and increase spore dormancy in Sphagnum (Fan et al., 2023 ). In our study, both WTD and pH are with small span, 5–19 cm for the former and 5.3–6.1 for the latter.…”

“…The characterized ecological gradients affect ecological processes in peatlands (Rydin & Jeglum, 2013 ). For example, the germination of seeds (Fernández‐Pascual, 2016 ; Liu et al., 2005 ) and spores (Fan et al., 2023 ; Feng et al., 2018 ; Sundberg & Rydin, 2000 ) is strongly depressed by hypoxia in hollows with low water table depth. In Sphagnum dwelling peatlands, the strong acidity due to cation exchange by Sphagnum is believed as the main mechanism to suppress seed germination and then vascular plant colonization (van Breemen, 1995 ) even though spore germinability (represented by germination percentage) decreases with pH in Sphagnum (Feng et al., 2018 ).…”