Water stress effects on successional populations of the dioecious herb, Rumex acetosella L.

Abstract

The effects of water stress and rewatering on the water relations and biomass of male and female plants of the dioecious herb, Rumex acetosella L., have been examined. Plants were collected from two fields, 2 and 15 yr old respectively, and submitted to different water regimes. Male plants from both populations showed a similar response to water deficit, having a low transpiration rate and low consumption of soil water, whilst maintaining a high green leaf area. Females from the two populations differed from each other more than males, both in terms of their response to drought and survival capacity. Females from the young population, which had a small green‐leaf area and a small root biomass, had progressively lower water potentials and maintained higher levels of transpiration at the onset of the first drought period, indicating a progressive acclimation to water stress. They also recovered more rapidly and to a greater extent than all the others upon rewatering. Females from the old population, with a high root/shoot ratio, transpired the most prior to the onset of water stress. They maintained a high water potential throughout the stress period, having high stomatal resistances and removing more water as soil moisture declined. This is indicative of drought avoidance. Root development was, however, limited in the shallow pots, hence the water resource was depleted rapidly and mortality occurred to a greater extent in these old‐field females. These characteristics may be adaptative, given the selection pressures which operate on water balance characters along a successional gradient and the spatial segregation of sexes that has been previously observed in this dioecious species in the same old‐field succession, with the sex ratio becoming progressively male‐biased with time. Copyright © 1992, Wiley Blackwell. All rights reserved