Phenology, biomass and nutrients of Imperata cylindrica and Desmostachya bipinnata along the water courses in Nile Delta, Egypt

Abstract

Pollution with heavy metals is a major environmental problem, and plants that accumulate these metals might provide efficient and ecologically sound approaches for their removal. Therefore, the present study was conducted to investigate the phenological behavior and the potential to accumulate nutrients and heavy metals in the aboveground phytomass of two perennial grasses (Imperata cylindrica and Desmostachya bipinnata) along the watercourses in Nile Delta, Egypt. Twenty-five quadrats were selected seasonally, to represent the growth of the two grasses, along canals and drains of the Nile Delta. The phenological behavior of the studied species showed similar seasonal trends along the canals and drains. The average annual biomass of the living and dead parts of D. bipinnata (1901.3 g m−2) was higher than that of I. cylindrica (1626.4 g m−2). D. bipinnata accumulated higher concentrations of Na, and K (14.3, 26.2 mg g−1), while lower Ca, Mg, N, P and Fe (14.2, 11.4, 10.8, 0.3 and 1.4 mg g−1) than I. cylindrica (12.8, 24.8, 14.4, 14.7, 11.6, 0.4 and 2.0 mg g−1). The living parts of I. cylindrica accumulated the highest contents of carbohydrates and proteins during autumn and spring, respectively, while those of D. bipinnata had the highest ash content, but the lowest lipids during summer. D. bipinnata accumulated higher concentrations of Cu and Mn, but lower of Zn and Pb, than I. cylindrica in their living and dead parts. Heavy metals, except Zn, had BF more than unity, however, the uptake capability was in the order: Pb > Mn > Cu > Zn for I. cylindrica, while Pb > Cu > Mn > Zn for D. bipinnata. The analysis of the nutritive values for the two studied grasses evaluated them as poor forage. Finally, the high bioaccumulation factors of both species for Mn, Cu and Pb, in addition to their ability to accumulate the highest concentrations of macro- and micronutrient in the dead parts, render these species a powerful phytoremediator for the removal of these metals from contaminated ecosystems.