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 greenleaf 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 oldfield 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 malebiased with time.

Differential drought tolerance of five coexisting plant species in Mediterranean lowland grasslands

“…The ability of the late-season Chrysopogon to reduce the water loss from its tissues is well documented by Noitsakis & Nastis (1985), who found that this species maintains high turgor potential because of the rigidity (high elasticity module) of the cell wall. The mid-season species Rumex also responds to water deficit by restricting water loss and maintaining higher values of RWC a behaviour which resembles the C plants (Houssard et al, 1992). Because leaf water potential is positively related to soil matric potential, the earlyseason species are thought to be more sensitive to water deficit.…”

Sexual Dimorphism in Life History

“…In a review of the literature I found relevant information on 47 species, including a quantification of the amount of biomass invested in reproduction per reproductive bout by both sexes for 29 species (Table l). For a further four species, Chamaedorea bartingiana, Ilex montana, Nyssa aquatica, and Phoradendron tomentosum, information Dawson et al, (1990) juniperinum Phoradendron P>M P>M P>M Nixon and Todzia (1985) tomentosum Rhamnus Guitian (1995) alaternus Rubus Agren (1987Agren ( , 1988 chamaemorus Rumex acetosa Putwain and Harper (1972); Korpelainen (1991Korpelainen ( ,1992 Korpelainen (1991Korpelainen ( , 1992; Houssard et al (1992Houssard et al ( , 1994 Alliende and Harper (1989) a Growth rate differs depending on soil moisture, with females growing more than males in streamside populations and males more in nonstreamside populations . Note that sex ratio also varies along with soil moisture.…”

The Biology of Canadian Weeds. 149. Rumex acetosella L.

“…Soil moisture level of 60% reduced both photosynthetic rate and leaf conductance in both males and females. Houssard et al (1992) reported a differential response to moisture stress in male and female plants collected from 2-and 15-year-old successional sites. Males from both sites had reduced transpiration and water consumption rates under drought conditions.…”

“…The ability to reproduce from creeping roots and its long-lived soil seed bank allows this species to easily withstand fire disturbance (Esser 1995). The well-developed root system also offers protection from drought; male individuals are typically more drought tolerant than females, which is likely due to the increased allocation of resources to vegetative growth in males (Zimmerman and Lechowicz 1982;Houssard et al 1992;Fujitaka and Sakai 2007). The low growth profile of the basal rosette of R. acetosella provides the plant with some protection from mowing or grazing (Anonymous 2006).…”

“…Over time, however, populations progress back towards a 1:1 ratio, in part because males and females occupy partially different ecological niches (Putwain and Harper 1972). Males can be more tolerant to water stress, which can promote a male-biased sex ratio under drought conditions (Houssard et al 1992). Males also devote more resources to vegetative reproduction than females, with the latter putting greater effort into sexual reproduction and developing a taller canopy structure.…”