Floating ability, shoot length and abundance facilitate hydrochorous dispersal of moss and liverwort fragments

Abstract

Question Vegetative diaspores are pivotal to the ability of bryophytes to colonize new areas, but life‐history traits and other factors facilitating vegetative hydrochorous dispersal are largely unknown. Here, we ask whether hydrochorous dispersal of vegetative bryophyte fragments can be predicted by specific traits in addition to discharge and abundance of species in the vegetation. Location The Twentekanaal, a navigation canal in the Netherlands. Methods Over a one‐year period, viable bryophyte fragments dispersed in the canal were quantified using a 200‐μm net and related to five potentially predicting variables. These variables are fragment buoyancy, shoot length, growth form, abundance in the vegetation and discharge. Buoyancy of fragments including regeneration was determined experimentally for all species found; other traits were derived from the literature. A Generalized Linear Mixed Model approach was adopted to identify the traits and trait–discharge interactions best explaining the presence of fragments in water. Results Of the 144 samples collected, 77% contained bryophyte fragments. A total of 54,514 fragments were counted, representing 18 species. The free‐floating Riccia fluitans was the most abundant species, followed by Brachythecium rutabulum. In total, 55% of the variation in diaspore presence of sessile species could be explained by abundance in the vegetation, buoyancy and shoot length. Of the sessile species of which fragments were trapped, mean floating time (T50) was 5.9 days and mean shoot length 79 mm. Species that occurred in the vegetation, but were not found in the water had a significantly lower buoyancy and shoot length. Conclusions We conclude that abundance in the vegetation, buoyancy and shoot length are significant predictors for vegetative hydrochorous dispersal of aquatic and riparian bryophytes. As fragments of species found are able to regenerate after being in water for weeks, they may contribute to colonization of new favourable substrate patches along water bodies after being dispersed.

Plant Dispersal in a Temperate Stream by Fish Species With Contrasting Feeding Habits: The Role of Plant Traits, Fish Diet, Season, and Propagule Availability

“…Nurminen et al (2003) has previously shown bryophytes to be part of the diet of Rudd, but these authors did not establish viability of egested fragments. Our study thus presents the first evidence that ichthyochory may significantly contribute to vegetative dispersal of several aquatic and riparian moss species, confirming earlier assumptions by Glime (2017) and complementing dispersal by hydrochory (Boedeltje et al, 2019). Given the small size (0.2-0.4 mm) of egested moss fragments, and that they were found throughout the year, we hypothesize that bryophytes were ingested when fish were foraging in the soft sediment (including the propagule bank with moss fragments) or feeding on invertebrates living in moss cushions on submerged stones in the stream (cf.…”

“…Wet filter papers in petri dishes also were used as regeneration substrate for vegetative parts of bryophytes (Boedeltje et al, 2019; Figure S3). The closed dishes were exposed to natural day light conditions (without direct sunlight) in an unheated room (mean temperature 18 • C) and watered with tap water when necessary.…”

“…Plant propagule uptake, egestion and dispersal may also depend on plant traits such as seed size (Pollux et al, 2007), seed hardness and seed shape (Boedeltje et al, 2015). However, the abundance of plant species in the local vegetation might also be important, as was demonstrated for hydrochorous plant dispersal (Boedeltje et al, 2003(Boedeltje et al, , 2019.…”

The hydrochorous dispersal of plant propagules in a giant river reservoir: Implications for restoration of riparian vegetation

“…Most of the previous studies on hydrochory are mainly performed in natural water bodies, such as rivers, streams, lakes, or in non‐natural agricultural ditches (Andersson et al, 2000; de Jager et al, 2019; Riis & Sand‐Jensen, 2006; Soomers et al, 2010; Su et al, 2019). These studies have found that the dispersal characteristics of hydrochorous propagules are determined by extrinsic and intrinsic factors (Chambert & James, 2009; Nilsson et al, 2010), such as hydrologic regimes, channel morphology, instream obstacles, flow velocity (Bång et al, 2007; Merritt & Wohl, 2002; Riis & Sand‐Jensen, 2006), meteorological conditions (Sarneel et al, 2014; Soomers et al, 2010; Su et al, 2019) and propagule buoyancy (Boedeltje et al, 2004, 2019; Nilsson et al, 2010). The relative importance of those factors varies among different types of water bodies.…”

“…Wind, however, usually becomes the dominant factor in lentic water bodies (Sarneel et al, 2014; Soomers et al, 2010) since the wind can blow through longer distances without meeting instream obstacles and thereby becomes stronger (Nilsson et al, 2002). Propagule buoyancy is an important intrinsic factor affecting dispersal distance (Boedeltje et al, 2004, 2019; Riis & Sand‐Jensen, 2006).…”