RESUMO
Patterns of variation at selected isozyme loci were examined in populations of Cistus albidus L. in south-east Spain, from areas differing in precipitation and temperature, to determine whether population divergence has occurred. Total genetic diversity was high, with a high percentage of the variation being found between populations. Genetic variation between populations did not relate to climate. Populations exposed to severe summer drought did not show lower genetic diversity than populations from more benign climates. Little genetic variation was found between populations that showed variation in ecophysiological and growth responses in situ and under controlled conditions. Cluster analyses showed different patterns of between-population distances with respect to genetic, physiological and morphological data, and none of these patterns corresponded to that for between-site environmental variation.
RESUMO
The ecophysiology of Cistus albidus L. plants in a variety of habitats in south-east Spain was measured in situ over the course of a year, to determine whether physiological variation occurs between populations growing in sites exposed to differing temperature and precipitation. Not all the observed variation could be explained by differing contemporary meteorological conditions. In particular, plants at the driest site maintained much higher photochemical efficiency through the summer and autumn than plants at the other sites, and also showed higher stomatal conductance after the autumn rains. Principal component analysis identified photochemical efficiency as the greatest source of variation between populations. Such variation may represent the result of differing selection in populations that have been exposed to different prevailing conditions of mean temperature, precipitation or atmospheric humidity, for long periods of time.
RESUMO
Seeds of Cistus albidus L. plants from three populations that are exposed to differing temperature and precipitation in Almería province of south-east Spain, were collected and grown together in a factorial experiment with two irrigation treatments. The aim was to determine whether populations from different habitats differed when exposed to common conditions, or differed in the plasticity of their response to availability of water. Significant differences in growth of branches and in leaf dimensions were found between treatments, indicating phenotypic plasticity. There was also significant variation between populations in growth of branches and leaf dimensions, with a population from a location that is intermediate in terms of precipitation and temperature showing the greatest growth of branches and production of leaves under the well-watered treatment. This population is from a semi-arid climate, where precipitation is unpredictable, and selection may have occurred to favour rapid growth when water is available. This population had the narrowest leaves under both treatments, and the lowest leaf mass in the well-watered treatment. It also maintained the same mass per leaf under the two treatments, whereas the others showed an increased mass of leaves with increased availability of water. Thus, populations differed both in their manner of allocating resources and their response to availability of water.
