Episodic but ample sporophyte production in the moss Drepanocladus turgescens (Bryophyta: Amblystegiaceae) in SE Sweden

In the Baltic area, the long-lived dioicous wetland moss Drepanocladus turgescens (T.Jensen) Broth. produces sporophytes rarely and at irregular intervals. Based on surveys of sporophyte occurrences at 13 sites in two regions in northern Gotland (Sweden) during three to five years, we ask: (1) Is sporophyte formation associated with precipitation and a precipitation index that considers the dry periods during July-August of the preceding year, when gametangia are formed and fertilization occurs? (2) Does the estimated spore output suffice for the species’ long-term persistence of the (Northern) European population species? In one of the study regions, where D. turgescens occurs in depressions, sporophyte formation was associated with the two precipitation parameters. In the other study region, with relatively higher precipitation and exposed occurrences on a slightly sloping bedrock with very little accumulated soil, no such association existed. We suggest that this lack of weather effects results from that the exposed rock habitat requires longer continuously wet periods than the depression habitat to allow for gametangia initiation and development, and fertilisation. Average spore production for six spore capsules, from three Gotland localities was 181,000. Based on the sporophyte counts during the survey years, we estimated the total reproductive output as 411.5 million spores in 2013, and 42.5 million in 2015, in the two respective study regions. Taken together with data on haplotype patterns and considering observations on recent colonisations, we argue that such a relatively low and episodic regional spore production is sufficient to maintain global populations of long-lived species, even if these occur in specialized and geographically restricted habitats.