Measuring spore settling velocity for an improved assessment of dispersal rates in mosses.
The settling velocity of diaspores is a key parameter for the measurement of dispersal ability in wind-dispersed plants and one of the most relevant parameters in explicit dispersal models, but remains largely undocumented in bryophytes. The settling velocities of moss spores were measured and it was determined whether settling velocities can be derived from spore diameter using Stokes' Law or if specific traits of spore ornamentation cause departures from theoretical expectations.



A fall tower design combined with a high-speed camera was used to document spore settling velocities in nine moss species selected to cover the range of spore diameters within the group. Linear mixed effect models were employed to determine whether settling velocity can be predicted from spore diameter, taking specific variation in shape and surface roughness into account.



Average settling velocity of moss spores ranged from 0·49 to 8·52 cm s(-1) There was a significant positive relationship between spore settling velocity and size, but the inclusion of variables of shape and texture of spores in the best-fit models provides evidence for their role in shaping spore settling velocities.



Settling velocities in mosses can significantly depart from expectations derived from Stokes' Law. We suggest that variation in spore shape and ornamentation affects the balance between density and drag, and results in different dispersal capacities, which may be correlated with different life-history traits or ecological requirements. Further studies on spore ultrastructure would be necessary to determine the role of complex spore ornamentation patterns in the drag-to-mass ratio and ultimately identify what is the still poorly understood function of the striking and highly variable ornamentation patterns of the perine layer on moss spores.
Department of Conservation Biology and Evolution, Institute of Botany, University of Liège, Sart Tilman, Liège, Belgium f.zanatta@doct.ulg.ac.be.
Florian
F
Zanatta
Department of Conservation Biology and Evolution, Institute of Botany, University of Liège, Sart Tilman, Liège, Belgium Island Ecology and Evolution Research Group, Instituto de Productos Naturales y Agrobiología (IPNA-CSIC), La Laguna, Tenerife, Canary Islands, Spain.
Jairo
J
Patiño
Biosystems Engineering Department, Gembloux Agro-Bio Tech, University of Liège, Gembloux, Belgium.
Frederic
F
Lebeau
Biosystems Engineering Department, Gembloux Agro-Bio Tech, University of Liège, Gembloux, Belgium.
Mathieu
M
Massinon
Department of Ecology, Environment and Plant Sciences, Stockholm University, Stockholm, Sweden.
Kristofer
K
Hylander
Department of Cryptogamy, National Botanic Garden of Belgium, Meise, Belgium.
Myriam
M
de Haan
Department of Cryptogamy, National Botanic Garden of Belgium, Meise, Belgium.
Petra
P
Ballings
Department of Cryptogamy, National Botanic Garden of Belgium, Meise, Belgium.
Jerôme
J
Degreef
Department of Conservation Biology and Evolution, Institute of Botany, University of Liège, Sart Tilman, Liège, Belgium.
Alain
A
Vanderpoorten
D044002:Bryophyta / Q000502:physiology*; D008954:Models, Biological; D063148:Plant Dispersal; D013170:Spores; D014919:Wind
Bryophytes; Law; Stokes’; drag; life-history strategy; moss; perine; settling velocity; spore diameter; spore ornamentation; wind dispersal