Reacute;gulations hydriques compareacute;es de populations deRumex acetosellale long d'un gradient successionnel postcultural

摘要

Two sets of plants ofRumex acetosellaL. of known sex (males and females in the same proportions), belonging to populations from two fields that were abandoned 2 and 15 years ago, were grown on soil regularly watered to field capacity or to half of field capacity. Four harvests of six plants for each sex, population and treatment were performed to follow the changes in biomass allocation to aerial and subterranean organs as related to plant water potential. In well-watered plants, the old population had a higher rate of water use than the young one because of rapid leaf surface area development and a higher root/shoot biomass ratio, which should make it more competitive in situations of strong interspecific competition, such as the late stages of succession. When plants were subjected to water stress (half of field capacity), clear-cut differences appeared between males and females at the vegetative stage. Female plants showed a good regulation of water balance and reached higher biomass values than male plants. However, flowering and fruiting induced a decrease in the root/shoot biomass ratio and in the transpiration rate of female plants, which would tend to exclude them with time. These results may explain the fact the the oldestRumex acetosellacommunities consist predominantly of males.