Effect of the intensity and phenophase of defoliation and water stress on the rate of photosynthesis and the recovery of carbohydrate reserves inacacia karroohayne

Abstract

To cite this article: W.R. Teague (1988) Effect of the intensity and phenophase of defoliation and water stress on the rate of photosynthesis and the recovery of carbohydrate reserves in acacia karroo hayne, Journal of the Grassland Society of Southern Africa, 5:4, 223-226, ABSTRACTA field study was conducted with Acacia karroo plants to determine changes in relative photosynthetic rates, the extent of carbohydrate reserve depletion and the rate reserves take to recover, following defoliation by goats at different intensities and phenophases, at a "wet" and a "dry" site.The rate of photosynthesis of fully expanded leaves increased markedly following defoliation. Light defoliation increased photosynthetic rate the most. Total non-structural carbohydrate levels dropped significantly after defoliation. The magnitude of decrease was directly related to the intensity of defoliation.Following the heavy defoliations, recovery of carbohydrate levels was much faster than after the light defoliations. Rates of recovery were also faster following defoliation in the second half of the growing season, than in the first half. However, the plants that had been heavily defoliated in the second half of the growing season had not fully recovered carbohydrate levels before leaf fall in late autumn.Moisture stress had very little effect on carbohydrate levels in comparison with the defoliation treatments. UITTREKSEL 'n Veldstudie is opAcacia karroo plante uitgevoer om verskille in relatiewe fotosintetiese tempo, die mate van koolhidraatreserwe vermindering en die tempo van herstel, na ontblaring teen verskillende intensiteite enfenofases, op 'n "nat" en 'n "droë" terrein, te bepaal. Na ontblaring, het die Fotosintese-tempo van volwasse blare, opvallend verhoog. Ligte ontblaring het die fotosintesetempo die meeste verhoog. Die totale nie-strukturele koolhidraat-vlakke het opvallend gedaal na ontblaring. Die grootte van dating is direk eweredig aan die intensiteit van ontblaring. Herstel van koolhidraatvlakke na strawwe ontblaring was baie vinniger as na ligte ontblaring. Die tempo van herstel van koolhidraatreserwes na ontblaring in die tweede helfte van die groeiseisoen was vinniger as gedurende die eerste helfte. Die koolhidraatreserwes van plante wat gedurende die tweede helfte van die groeiseisoen straf ontblaar is, het gedurende die daaropvolgende laat herfs nog nie volkome herstel nie. In vergelyking met die ontblaringsbehandetings, het vogstremming 'n minimale invloed op die koolhidraatvlakke gehad.

Effects of moisture, nitrogen, grass competition and simulated browsing on the survival and growth of Acacia karroo seedlings

“…Of all the treatment interactions, wherever the seedlings were subjected to grass competition, they were suppressed irrespective of increased moisture and nitrogen fertilization. The results are consistent with the findings from other studies, which showed that grass competition significantly reduces the growth of A. karroo seedlings (Teague, 1988, 1992; Chirara, 2001). Irrigation significantly interacted with grass competition and the mean stem length of nonirrigated A. karroo seedlings was higher than the irrigated ones.…”

“…The results of this study showed that the irrigated seedlings had better growth performance, irrespective of other factors with which irrigation interacted. Similar experiments have also indicated that A. karroo seedlings are sensitive to moisture, and thus require adequate water to grow and become successfully established (Teague, 1988, 1992; O’connor, 1994; Chirara, 2001). The results of this study are also consistent with the nonequilibrium model proposed by Higgins, Bond & Trollope (2000), which states that the recruitment of woody plants in savannas is controlled by rainfall.…”

“…In this experiment, defoliation by clipping did not have a significant effect on the survival of the seedlings. Generally, seedlings are most sensitive to browsing below the cotyledon stage (Story, 1952; Teague, 1988), at the time of switching dependence for nutrients from the cotyledons to roots (Scogings, 2003). This may be an explanation for the tolerance of clipping by seedlings, which were not competing with grass because they were clipped when they were already above the cotyledon stage.…”

“…According to Oldeman & Tomlinson (1978), mortalities among seeds and seedlings are much higher than in any other ontogenic stage, so certain speculations can be made concerning the causes of such an outcome. There is substantial evidence in the literature to suggest that soil moisture and nutrients greatly influence the survival and overall performance of plants in savanna ecosystems (Teague, 1988; O’connor, 1994; Flyman, 1999; Breebaart et al. , 2001; Kranz, 2001).…”

Chemical and mechanical defense against herbivory in two sympatric species of desert Acacia

“…Interestingly, Du Toit et al (1990) found that the chemical defences of A. nigrescens were lower near waterholes than at control sites. This result was related to obvious differences in browsing levels, but could also be a consequence of differences in regrowth capacity that is dependent on the availability of water (but see also Teague 1988). Further research is required on the effect of variations in water supply on plant defences.…”