Evolutionary considerations of claims for physical dormancy-break by microbial action and abrasion by soil particles

Abstract

Abstract Books and review articles in various areas of ecology and seed and plant biology continue to report that dormancy-break in seeds (and fruits) with water-impermeable coats (i.e. physical dormancy) occurs via soil-microbial action and/or abrasion by soil particles. However, there is little evidence in the scientific literature to support these assumptions, which, in fact, do not make good evolutionary sense for two related reasons. First, several types of anatomically specialized water-restriction structures have evolved as part of the seed or fruit coat of taxa with physical dormancy. These structures act as ‘signal detectors’ of physical-environmental changes that cause seeds (and fruits) to become water-permeable only at these sites, in seasons and habitats in which there is a good chance that some seedlings will become established. Second, seed (and fruit) coat breakdown by microbial action or by abrasion likely would occur in seasons and habitats in which seedlings could not survive, thus lowering the fitness (λ) of the plant taxa in question.