The effect of elevated CO₂ and grazing by Gastrophysa viridula on the physiology and regrowth of Rumex obtusifolius

Abstract

SUMMARYPlants of Rumex obtusifolius L. were grown in Solardomes under ambient and elevated (+ 250 /;mol mor') mole fractions of CO^ and were exposed to two levels of herbivory by Gastrophysa viridula Degeer larvae. The herbivory treatment lasted 1 month, thereafter half of the plants were harvested and over the following month during a period of regrowth physiological measurements were made on the remaining plants. At the termination of the herbivory treatment uninfested plants showed no damage, whereas the low-and high herbivore treatments caused 20-40 °o and 50-70 "o loss of leaf area as a proportion of total leaf area, respectively. The CO., treatment did not affect the degree of defoliation. Total leaf area was not significantly affected by either CO., or herbivory. Uninfested plants grown in elevated concentrations of CO, showed increased growth, root-to-shoot ratios (RS), rates of photosynthesis and reduced stomatal conductance compared with uninfested plants grown in ambient CO.^. A/Canalysis revealed that plants grown in elevated CO, showed reductions in I c^^^. For plants grown in ambient CO, the high herbivory treatment led to increased rates of photosynthesis and decreased rates of dark respiration per unit leaf area, and caused increases in stomatal conductance and RS. For plants grown in elevated CO., the high herbivory treatment increased plant biomass and RS. The increases in RS in response to elevated CO, and herbivory appeared to be additive. Defoliation did not reduce the degree of photosynthetic down-regulation caused by growth in elevated concentrations of CO,, but appeared to reduce the rate of ontogenic decline in photosynthesis in ambient CO,.

Elevated CO 2 enhances resprouting of a tropical savanna tree

“…Symbols for comparison of treatments on specific harvest dates: NS (not significant), *0.05>P>0.01, **0.01>P>0.001, ***P<0.001 Therefore, CO 2 stimulated regrowth independently of the effects of CO 2 on pre-clipping size. Other studies have that found CO 2 stimulates resprouting following defoliation (Fajer et al 1991;Wilsey et al 1994Wilsey et al , 1997Pearson and Brooks 1996) and coppicing (Will and Ceulemans 1997), but in these studies, the effect of CO 2 was not greater for clipped than unclipped individuals. In agreement with the current study, Kruger et al (1998) found the CO 2 effect to be greater for defoliated Acer saccharum.…”

Gastrophysa viridula (Coleoptera: Chrysomelidae) and biocontrol of Rumex - a review

“…However, previous herbivory reduces the infection of Rumex leaves by U. rumicis (Hatcher et al 1994, Hatcher andPaul 2000). Air CO 2 content that is expected to increase may also influence leaf acceptability (Pearson andBrooks 1996, Brooks and.…”

“…Even the seedlings established few weeks before the herbivory, of which 90% leaf area was removed, were able to recover (Hatcher 1996). However, size, root to shoot ratio (Pearson andBrooks 1996, Hatcher 1996), and seed production and quality (Bentley et al 1980) of regrown plants are influenced. Negative effects of herbivory are exaggerated in plants exposed to interspecific Table 6.…”

Influences of atmospheric CO2 enrichment on the responses of sugar maple and trembling aspen to defoliation

“…For example, in future atmospheric conditions, sugar maple might be more capable of tolerating severe defoliation events which in the past have been implicated in widespread maple declines (Houston, 1987). Furthermore, based on data from this and other studies (Ryle & Powell, 1992 ;Pearson & Brooks, 1996), we suggest that the potential of elevated CO # to stimulate plant growth and ecosystem productivity might be fully realized only in the presence of stresses, such as herbivory, that decrease the assimilate source : sink ratio in the plant.…”