Assessment of metal concentrations, chlorophyll content and photosynthesis in Phragmites australis along the lower Diep River, CapeTown, South Africa

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