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

Books and review articles in various areas of ecology and seed and plant bi ology continue to report that dormancy-break in seeds (and fruits) with wat er-impermeable coats (i.e. physical dormancy) occurs via soil-microbial act ion 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 t ypes of anatomically specialized water-restriction structures have evolved as part of the seed or fruit coat of taxa with physical dormancy. These str uctures act as 'signal detectors' of physical-environmental changes that ca use seeds (and fruits) to become water-permeable only at these sites, in se asons and habitats in which there is a good chance that some seedlings will become established. Second, seed (and fruit) coat breakdown by microbial a ction or by abrasion likely would occur in seasons and habitats in which se edlings could not survive, thus lowering the fitness (lambda) of the plant taxa in question.