Germination ecology of eleven species of <I>Geraniaceae</I> and <I>Malvaceae</I>, with special reference to the effects of drying seeds

Abstract

Germination and survival of water-impermeable seeds of 11 species of Geraniaceae and Malvaceae were monitored during dry storage and during burial in soil for up to 2.5 years. During dry storage, seeds of annual Geraniaceae became permeable and also lost their physiological dormancy. However, during burial in natural conditions, most seeds remained impermeable and viable, with no seasonal change in germination capacity. Germination in only one species (Geranium robertianum) was enhanced by daily alternating temperatures when seeds were exhumed in spring. Drying of exhumed seeds broke physical dormancy. Seeds of the perennial Geranium pratense gradually became permeable in a prolonged germination test of 31 weeks. Most seeds of Malva remained impermeable during dry storage. Buried seeds gradually germinated in situ, and exhumed seeds had a low germination capacity in all seasons. We concluded that dormancy of hard seeds in natural conditions may be broken by drying during summer, by specific temperature regimes or by gradual softening of the seed coat, ensuring the spread of germination over many seasons.

Environmental signals for seed germination reflect habitat adaptations in four temperate Caryophyllaceae

“…Dry storage was the most effective pre‐treatment for breaking dormancy in seeds of S. graminea . After‐ripening during dry storage has been shown to be an important mechanism regulating dormancy in winter annuals, preventing germination in dry summer months (Van Assche & Vandelook 2006). A stimulating effect of dry storage was also found in a large number of temperate grassland species surveyed by Grime et al .…”

Physical dormancy in a changing climate

“…Loss of physical dormancy is often directly related to temperature, with an increasing proportion of any seed lot losing dormancy as temperature increases (Martin et al, 1975;Auld and O'Connell, 1991;Van Assche and Vandelook, 2006;Ooi et al, 2012). The temperature experienced by the seeds once they are on the soil surface or in the seed bank, and the dormancy-breaking conditions that the seeds require, combine to ensure germination occurs during the best period for recruitment.…”

“…Secondly, physical dormancy can allow long-term seed banks to develop (Norman et al, 2002;Van Assche and Vandelook, 2006;Ooi, 2012;Ooi et al, 2012;Baskin and Baskin, 2014), and any alteration of PY traits by projected environmental changes may affect the functioning of these long-term seed banks. And thirdly, relatively little is known about the degree of variability in PY within wild species.…”

Physical dormancy and histological features of seeds of five Acacia species (Fabaceae) from xerophytic forests in central Argentina

“…Therefore, the differences in the histochemical and physiological characteristics of the seed coat of the five Acacia species indicate that each species has special germination requirements and might have different use of microhabitat resources (Bazzaz, 1991;Van Assche and Vandelook, 2006). Such differences suggest the existence of interspecific differences in regenerative niches, which could promote coexistence of these five species of Acacia in the xerophytic forest of Cordoba, Argentina (Daws et al, 2002;Grubb, 1977).…”