Ecological correlates of ex situ seed longevity: a comparative study on 195 species

Abstract

Background and aims: Extended seed longevity in the dry state is the basis for the ex situ conservation of 'orthodox' seeds. However, even under identical storage conditions there is wide variation in seed life-span between species. Here, the effects of seed traits and environmental conditions at the site of collection on seed longevity is explored for195 wild species from 71 families from environments ranging from cold deserts to tropical forests.

Methods: Seeds were rapidly aged at elevated temperature and relative humidity (either 45 degrees C and 60% RH or 60 degrees C and 60% RH) and regularly sampled for germination. The time taken in storage for viability to fall to 50% (p(50)) was determined using Probit analysis and used as a measure of relative seed longevity between species.

Key results: Across species, p(50) at 45 degrees C and 60% RH varied from 0.1 d to 771 d. Endospermic seeds were, in general, shorter lived than non-endospermic seeds and seeds from hot, dry environments were longer lived than those from cool, wet conditions. These relationships remained significant when controlling for the effects of phylogenetic relatedness using phylogenetically independent contrasts. Seed mass and oil content were not correlated with p(50).

Conclusions: The data suggest that the endospermic seeds of early angiosperms which evolved in forest understorey habitats are short-lived. Extended longevity presumably evolved as a response to climatic change or the invasion of drier areas. The apparent short-lived nature of endospermic seeds from cool wet environments may have implications for re-collection and re-testing strategies in ex situ conservation.

Fig. 1.

Survival curves fitted by probit analysis for four of the species in this study: seeds of (A) Tofieldia pusilla, Blackstonia perfoliata and Calothamnus crassus aged at 60% RH and 45°C, and (B) Calothamnus rupestris aged at 60% RH, 60°C and 60% RH, 45°C (inset).

Fig. 2.

Box plots of p₅₀ in (A) orders and (B) families. Only orders and families with three or more species tested are shown. Boxes span the 25th to 75th percentiles; whiskers span the 5th to 95th percentiles.

Fig. 3.

Box plots comparing p₅₀ for endospermic and non-endospermic seeds. Boxes span the 25th to 75th percentiles; whiskers span the 5th to 95th percentiles.

Fig. 4.

Relationship between p₅₀ and (A) oil content, (B) seed mass, (C) annual temperature, and (D) annual rainfall.

Fig. 5.

Relationship between p₅₀ contrasts and (A) oil content contrasts, (B) seed mass contrasts, (C) annual temperature contrasts, (D) annual rainfall contrasts. Contrasts were generated in CAIC and the regressions were forced through the origin.