Population ecology of halophyte seeds

Some aspects of the population biology of halophytes are considered in this review. Persistent seed banks have been reported for a number of inland- and coastal-salt marsh plant communities. Seeds of perennial grasses are often under-represented, while annuals and some perennial forbs may be over-represented in the seed bank. The persistent seed bank of annual halophytes appears adaptive, and provides multiple seed germination opportunities which may prevent local extinction when environmental stress increases. Somatic seed polymorphism provides a mechanism by which parent plants can respond to changing environments by partitioning their resources into reproductive units which have distinct germination responses. Parental effects may influence either seed morphology and/or physiological requirements of seeds when they are exposed to environmental stress. A prolonged germination period can provide plant populations with numerous opportunities to establish seedling cohorts. Early cohorts will have a selective advantage under moderate conditions because mortality will be low and plants will survive until maturity. However, fluctuations in salinity levels and tidal activity can cause high mortality in early cohorts in salt marsh habitats, providing later cohorts with an opportunity for establishment. Resource allocation to reproductive structures is related to plant size, which itself can be affected by both abiotic and biotic factors. Larger plants were found to produce more seeds than smaller plants in a population, but the mean seed weight was greater in small plants. /// Cette revue examine quelques aspects de la biologie des peuplements des halophytes. On a observé qu'il y a des réserves permanentes de graines pour certaines populations de plantes de marais salants, tant sur le littoral qu' à l'intérieur des terres. Les réserves de graines tendent à présenter insuffisamment de graines de plantes vivaces et trop d'annuelles et de certaines herbacées vivaces. La reserve permanente des halophytes annuelles semble être adaptive, et offre aux graines de multiples occasions de germination, ce qui peut empêcher l'extinction locale quand le stress de l'environnement augmente. Le polymorphisme somatique de la graine offre un mécanisme par lequel les plantes-parents peuvent réagir à des environnements variables en subdivisant leurs ressources en des unités reproductrices qui ont des réactions de germination distinctes. Les plants précoces auront un avantage sélecti