Seed Entrapment in Alpine Ecosystems: Effects of Soil Particle Size and Diaspore Morphology

Abstract

The spatial distribution of diaspores in seed banks can be significantly affected by physical processes that act on diaspores after they reach the soil surface. We examined how diaspore morphology and soil particle size affect diaspore incorporation into soil in a disturbed alpine ecosystem on the Beartooth Plateau, Montana, USA. Diaspores of alpine species with varying morphology were sown over soils of five different particle sizes and later collected from three depths. Regardless of diaspore morphology, the total number of diaspores trapped increased with increasing particle size until a threshold soil particle size was reached above which no more diaspores were trapped. At small particle sizes (0.5—1.0 and 1.0—2.0 mm) small diaspores and diaspores with adhesive seed coats were trapped, but most large diaspores moved horizontally across the surface and were not trapped. The majority of those diaspores trapped were at the 0—1 cm depth at small particle sizes. At large particles sizes (2.0—4.0, 4.0—8.0, and 8.0—16.0 mm) high numbers of large diaspores were trapped, and more diaspores moved vertically through the soil column. In small particle size soils small diaspores reached greater depths than large diaspores. Diaspores with adhesive seed coats responded more like large diaspores in terms of vertical movement. Diaspore length and eccentricity (length/width) were highly correlated with entrapment at small particle sizes and appeared to have the greatest effect on horizontal movement. Mass and width were significantly correlated with numbers of diaspores trapped in large particle sizes and were influencing vertical movement. Models based on the Weibull probability distribution were used to describe diaspore "survival" on the soil surface and to describe vertical movement in the soil column. This study indicates that on exposed soils in windy environments diaspore morphology and soil particle size greatly affect the spatial distribution of diaspores in seed banks. For diaspores of a given species, the optimal soil type traps a high number of diaspores but precludes significant downward movement.

Spatial structure of the soil seed bank of Poa annua L.—alien species in the Antarctica

“…Therefore we might speculate that the local spread of P. annua in the future might largely depend on clump expansion rather than on the formation of new distinct clumps. The formation of new clumps is probably a stochastic phenomenon dependent on long distance seed dispersal, topography and surface soil characteristics favorable for seed entrapment and subsequent germination (Chambers et al 1991). Also human dependent seed transport may play a role in the species spread, similarly to the way in which seeds get transported to Antarctic research stations (see e.g.…”

Factors influencing the genetic structure of Phacelia dubia, a species with a seed bank and large fluctuations in population size

“…Secondary seed dispersal (Phase II of dispersal, Watkinson, 1978) is unlikely to be important in P. dubia because: (i) the seeds lack aerodynamic features that favour wind dispersal (see Burrows, 1986);(ii) even under high winds no seed movement was detected in the soil (R. F. del Castillo, personal observation) and (iii) small seed size, as that of P. dubia (0.8 mm length), increases the probability of the seed being trapped in soil (Chambers et al, 1991). Nevertheless, seed dispersal is not only affected by the physical properties of the plants and seeds but also by the habitat.…”

The fate of seeds in the soil: a review of the influence of overland flow on seed removal and its consequences for the vegetation of arid and semiarid patchy ecosystems

“…Our focus will be placed on drylands, because secondary dispersal has been recognized as a significant part of dispersal in environments with sparse vegetation (Nelson and Chew, 1977;Reichman, 1984;Chambers et al, 1991).…”