Moss cushions facilitate water and nutrient supply for plant species on bare limestone pavements

Abstract

Dense moss cushions of different size are distributed across the bare limestone pavements on Øland, SE Sweden. Increasing cushion size is predicted to physically protect and improve performance and colonization by vascular plants. Therefore, we tested water balance, phosphorus supply, and species richness, and evaluated duration of plant activity during desiccation as a function of ground area, for a large collection of moss cushions. We found that lower evaporation and higher water storage contributed equally to extending the desiccation period with increasing cushion size. Evaporation rates declined by the -0.36 power of cushion diameter, and were not significantly different from -0.50 for the square root function previously predicted for the increasing thickness of the boundary layer, with greater linear dimensions for smooth flat objects at low wind velocities. Size dependence vanished under stagnant conditions. One moss species was added to the species pool for every nine-fold increase in cushion area. Vascular plants were absent from the smallest cushions, whereas one or two species, on average, appeared in 375- and 8,500-cm(2) cushions with water available for 6 and 10 days during desiccation. Phosphorus concentrations increased stepwise and four-fold from detritus to surface mosses and to vascular plants, and all three pools increased with cushion size. We conclude that cushion mosses and cushion size play a critical role in this resource-limited limestone environment by offering an oasis of improved water and nutrient supply to colonization and growth of plants.

Plant–plant interactions change during succession on nurse logs in a northern temperate rainforest

“…In old‐growth forests in western Oregon, for example, seedling emergence was higher on nurse logs of decay class 3 (our class 2) when bryophytes were present than when they were removed (Christy & Mack, 1984), and in a field experiment in the Hoh rainforest testing the influence of moss depth on seedling density, seedling density of Tsuga was higher in a moss mat of 3.7 cm than in 1.4 cm or 7.8 cm (Harmon & Franklin, 1989). The positive effect of bryophytes on tree seedlings could be due to protection from herbivores, increasing moisture or nutrient availability, protecting seeds from being blown off by the wind, or providing a humus substrate into which seedling roots can grow (Graham & Cromack Jr., 1982; Harmon & Franklin, 1989; Nakamura, 1992; Sand‐Jensen & Hammer, 2012). Facilitation of tree seedlings may also be linked to bryophyte richness as greater species richness of bryophytes was found to have increased moisture absorption and retention (Rixen & Mulder, 2005).…”

Can bryophyte groups increase functional resolution in tundra ecosystems?

“…'Cushions', large and small, were also not represented by our data. Cushion growth is considered an adaptation to water conservation and low temperatures (Rice and Schneider 2004;Sand-Jensen and Hammer 2012). The WHC of 'Dendroid' bryophytes has not been studied but the dendroid life form is associated with habitats of relatively high moisture or humidity (Atherton et al 2010).…”

Ecological niches of epiphyllous bryophytes along Afrotropical elevation gradient

“…Ecologically, they inhabit diverse habitats from drylands to the humid tropics (Smith 2011), often as early pioneers of bare substrates (Man et al 2022). They affect nutrient and water balance (DeLuca et al 2002, Sand‐Jensen and Hammer 2012), decomposition (Hagemann and Moroni 2015) and soil environments (Van Der Wal and Brooke 2004), and their activity may facilitate the subsequent colonization of vascular plants and organisms of higher trophic levels (Gavini et al 2019, Doležal et al 2022a). As photosynthetic autotrophs extracting water and minerals from the atmosphere, bryophytes do not need soil to survive (Smith 2011) and many of them live as epiphytic plants on various substrates such as tree bark or rock (Sales et al 2016, Glime and Pócs 2018) and some also as epiphylls on the leaves of vascular plants.…”