Growth, reproduction and resource allocation in halophytes

Different patterns of growth and reproduction in halophytes are examined in relation to their ability to colonise saline habitats. In many halophytes, vegetative propagules are produced which establish as “ready-made plants”, thereby bypassing the uncertainties of seedling establishment. In other species where agamospermy is well developed, genetic variation both within and between populations is limited. Halophytic species that have this type of breeding system are extremely salt tolerant and an individual has the potential to give rise to a population of genetically uniform plants which are adapted to a narrow ecological niche. However, in a number of halophytes both genetic variation between populations and phenotypic plasticity of individuals occur as “mixed strategies”, enabling them to cope with environmental heterogeneity. The value of integrating studies of genetic variation in populations with molecular, biochemical and ecological studies is evident, and such an integrated approach appears to be directly applicable to studies of salt tolerance in plant populations. Phenotypic plasticity in response to a changing environment is likely to be well developed in long-lived perennial halophytes. Conditions at the time of establishment may be very different from those one or two decades later. Leaf plasticity has been examined in plants of Triglochin maritima L. grown at different salinities. A reduction in both the number and size of leaves per shoot, and changes in the nutrient and water contents of leaves, occurred as the salinity increased. Acclimation to increased salinity took at least 50 days before the relative birth rate of leaves per shoot of plants in the different saline cultures was similar. The significance of the different types of asexual reproduction and the phenotypic adjustments are discussed in relation to resource availability for plant growth at high salinities.