Abstract
Phragmites australis growing at 4 selected sites along the bank of the lower Diep River, Cape Town, South Africa and in adjacent soil was assessed for photosynthesis, chlorophyll content and metal concentrations in shoots and roots. The rate of photosynthesis was determined using the Infra - red gas analyzer (IRGA). Chlorophyll content of leaves was determined by extraction of the pigments using dimethyl sulphoxide (DMSO). Chlorophyll was quantified from the extract using a spectrophotometer (645 and 665 nm). Ten metals (cadmium, copper, iron, lead, manganese, nickel, zinc, aluminium, chromium, and cobalt) in the shoots and roots of Phragmites australis were measured by ICP-MS. The abundance of the metals were in the order Al > Pb > Cd > Co > Ni > Cr; and for micronutrients, Fe > Mn > Zn > Cu both in the shoots and roots from all the sites investigated. Chlorophyll a, b and total chlorophyll (Chl.T), as well as photosynthesis were significantly lower in P. australis from the river bank compared with the adjacent soil. Increased metal loads in plants from the river bank were found to accompany the decreasing chlorophyll concentrations and photosynthetic rate. More metals were found to be accumulated in plants on the river bank compared to plants from adjacent to the river bank.
Highlights
A cornerstone of ecotoxicological science is the ability to demonstrate a relationship between the exposure of metals and the physiological responses in plants
Phragmites australis growing at 4 selected sites along the bank of the lower Diep River, Cape Town, South Africa and in adjacent soil was assessed for photosynthesis, chlorophyll content and metal concentrations in shoots and roots
Results of this study revealed that plants from all the sites investigated were generally contaminated with all the metals measured
Summary
A cornerstone of ecotoxicological science is the ability to demonstrate a relationship between the exposure of metals and the physiological responses in plants (such as changes in chlorophyll content and photosynthesis activities). Metal pollution of plants growing in polluted environments in nature has been shown to be due to the presence of cocktail of several metals (Walker et al, 2003; Rodrίguez et al, 2007) They may exhibit toxicity simultaneously and interactively at different levels (Vάzquez et al, 2006). The extent to which physiological parameters in Phragmites australis (chlorophyll content, photosynthesis) and metal accumulation are affected at different sites along a pollution gradient in Diep River in Cape Town. Reeds (P. australis) are the focus of this study because it is the most abundant plant species lining the river banks along the Diep River It is widespread along South African rivers and commonly occurs in monospecific stands (Laing et al, 2003; Saltonstall, 2008)
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