Spore germination response to capsule size and smoke: co-expression of bet-hedging and best-bet strategies in peatland mosses

Abstract

Smoke-mediated spore germination in mosses is a fire-adaptive evolutionary trait that might control plant composition after fire. How capsule size, either alone or in combination with smoke, affects spore germination in peatland mosses remains unknown. We selected three peatland mosses, Sphagnum fuscum, S. squarrosum, and Polytrichum strictum and measured volumes of 40 capsules per species, categorizing them into large- and small-capsule groups. We then assessed spore diameters within each capsule group and examined how capsule size affects spore germination following smoke-water treatment. We found a positive correlation between capsule and spore size only in S. squarrosum. Spore viability was consistent across capsules in all species. Large-capsule spores had higher germination than small-capsule spores in Sphagnum. However, germination was slower in spores from large than small capsules in Sphagnum species, suggesting a trade off between germination percentage and germination speed. Smoke water enhanced germination speed in large-capsule but not in small-capsule spores in all species. Smoke water released dormancy in large-capsule spores of S. squarrosum and S. fuscum by 100 % and 45 %, respectively, which was significantly higher than that in small-capsule spores (33 % and 4 %). There was no such capsule size-dependent difference in P. strictum. The study suggests that the variation inspore germinability among capsules and consistency in smoke-responsive germination of spores, regardless of capsule size, represent dual expressions of bet-hedging (spreading germination time) and best-bet (germinating in best time) strategies in Sphagnum, enabling them to maintain population persistence in peatlands subject to natural and anthropogenic disturbances.

Keywords: Capsule size; Sphagnum; dormancy; germination; peatland; smoke water; spore size.