Emad A. Farahat

The effect of long-term wastewater irrigation on accumulation and transfer of heavy metals in Cupressus sempervirens leaves and adjacent soils.

Wastewater reuse for agriculture is an important management strategy in areas with limited freshwater resources, yielding potential economic and environmental benefits. Here the effects of long-term irrigation with wastewater on the nutrient contents of green and senesced leaves of Cupressus sempervirens L. were assessed for three planted forests in Egypt. Stoichiometric ratios, transfer factors for nutrients from soil to plant and enrichment factors in contaminated soils were estimated and compared to a ground water irrigated control site. Under wastewater irrigation, C. sempervirens transferred most of the estimated nutrients, particularly heavy metals, from green to senesced leaves. This could be a self-protecting mechanism under continuous wastewater irrigation. The accumulation of four metals (Zn, Mn, Cu and Cd) with transfer factors>1 for wastewater-irrigated trees, indicated the ability for metal accumulation of C. sempervirens. Stoichiometric ratios decreased under wastewater irrigation compared to the control site and global trends, which suggests nutrient disorders in these plants. The values of enrichment factors in the wastewater-irrigated soils showed remarkable availability and distribution of metals. Decreased resorption of metals by senesced leaves of C. sempervirens will add considerable amount of these metals to the soils, which will likely have adverse affects on the desert ecosystem components.

The invasive macrophyte Pistia stratiotes L. as a bioindicator for water pollution in Lake Mariut, Egypt

The present study was conducted to evaluate the potentiality of the aquatic macrophyte Pistia stratiotes to accumulate trace metals, perspective of phytoremediation, and the probability for using it as a bioindicator for the different pollution types. Plants were collected from the different Lake Mariut basins (main basin, south-west, north-west, and fish farm), through five quadrats each, for measuring some growth parameters such as plant density, rosette diameter and height, root length, number of living and dead leaves per individual, and leaf length and width. In addition, nutrients and heavy metals in plant organs as well as water samples were analyzed. The bioaccumulation and translocation factors of trace metals were calculated. Water physicochemical data of Lake Mariut showed significant variations of all variables, except temperature and pH as well as Cd metal, among the lake basins. Fish farm was characterized by the highest plant density, individual size, biomass, and the number of living leaves, while the north-west basin had the lowest, except the number of dead leaves. In contrast to trace metals, P. stratiotes accumulated concentrations of macronutrients in the leaves higher than in roots. The bioaccumulation factors of the investigated metals, except Cu, were greater than one, while the translocation factors (TFs) of all trace metals were less than unity, and this may render P. stratiotes suitable for rhizofiltration. In addition, the significant positive correlation of Ni and Cd in water with those in plant roots and leaves as well as the growth response of this plant to the different pollutants may suggest its potential use as bioindicator for these pollutants in water.

The biology of Calotropis procera (Aiton) W.T.

Key messageThis review article contributes in more understanding of most aspects ofCalotropis procerabiology and extend our knowledge about its behavior.AbstractCalotropis procera (Aiton) W.T (Asclepiadaceae) (Giant milkweed) is a xerophytic perennial shrub or small tree. It is native to tropical and subtropical Africa, Asia and common in the Middle East. It grows on a variety of soils, from fine to coarse texture, with varying degrees of salinity. The importance of C. procera in the functioning of ecosystems is reflected in its hosting of butterflies, while it also acts as a food plant for arthropods. In addition, it is used for medicinal purposes in many arid countries. Potential new uses of this species in semi-arid regions include the phytoremediation of soils contaminated with trace elements and the use of biomass as a source of renewable energy.

Demography and size structure of the giant milkweed shrub Calotropis procera (Aiton) W.T. Aiton

Studies on plant population demography and size structure provide important base for monitoring and managing plant species. The present study investigated the monthly variation in plant demography, population dynamics and size structure of Calotropis procera in urban areas, South Cairo, Egypt. Sixty-three permanent quadrats were selected to represent the monthly variation in the characteristics of C. procera population all over one year. The highest plant density was attained in June and the lowest in February and March. The highest biomass was recorded in November, but the lowest in March. The maximum individual’s height was recorded from August to January, while the minimum was in late winter. The monthly size distribution indicated that C. procera had three different size distributions along the whole year: more or less inverse J-shape, positively skewed and bimodal size distribution. The maximum plant survival was correlated with the availability of soil moisture. The demographic flux indicated that the new branches of plant were mainly formed during April and June, followed by significant mortality in July and October. This study may contribute in planning for managing and conserving this medicinal plant.