Phragmites australis and Typha orientalis in removal of pollutant in Taihu Lake, China

Two plant populations of Phragmites australis and Typha orientalis grown in gravel and sediment substrate were studied to assess their capabilities for purifying polluted water in Taihu Lake, China. The substrate displayed most significant effects on the suspended matter (P < 0.01), with the reduction of 76%-87% and 52%-63% for R australis, and 83%-86% and 45%-62% for T orientalis in gravel substrate and sediment substrate, respectively. Both species and substrates significantly decreased the N and P concentrations of water body (P < 0.01). R australis showed higher total N and P concentrations in tissues than T orientalis and had a greater potential to remove nutrients from the lake. Phosphate was easily to concentrate in the belowground tissues, while nitrate concentration was higher in leaf and stalk. Therefore, harvesting the aboveground tissues could take most of nitrate out of the sediment. The saturate photosynthetic rate (A(sat)) of P. australis was higher than that of T orientalis when grown in sediment substrate. But instance water-use-efficiency (WUEi) (A/E) and intrinsic water use efficiency (A/g(s)) showed the maximum values of two species grown in river water. With significant difference in g, however, intercellular CO2 concentration (C-i) had no obvious difference in two species which indicated that high A(sat) value of R australis might result from the increased carboxylation capacity of the mesophyll, because of the central role of N in photosynthetic enzymes. Our findings suggest that the plants could absorb most of nitrogen in polluted water, while gravel displayed a high capacity for absorbing the suspended matters and phosphate salts. Therefore, biological and physiological pathways for pollutant removal should be integrated.