الفهرس 
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Abstract
The research covered two important abiotic stresses, drought and heavy metal toxicity, which are the common adverse environmental conditions that have markable effects on crop productivity limitation worldwide. Suggestions of a promising alternative strategy to overcome the side effects which brought by abiotic stress and for better plant health and protection.
The first part worked on leaves and bark of trees as they are tools for assessing the effects of the heavy metals pollution and monitoring the environmental air quality. In this study, the possibility of using leaves and bark of two urban trees, namely, Ficus nitida and Eucalyptus globulus as a bioindicator of atmospheric pollution was evaluated by determining the composition of heavy elements in the tree leaves, bark, soil, and the atmospheric dust. Two common tree species, namely, F. nitida and E. globulus were selected in the heavily industrial zone of surrounding Minya governorate, Upper Egypt. Two urban areas with heavy traffic load (sites 1 and 2), three industrial zones (sites 3, 4, and 5) and an uncontaminated area as a control were selected (site 6). Sampling from leaf, bark, soil, deposited dust of trees was carried out in winter and summer seasons (from November 2016 to March 2017). The results reflected that the concentrations of heavy metals in dust, soil, leaves, and bark possess the same trend: Pb>Cu>Cd. The highest concentration of cadmium, lead, and copper was found in the leaf of F. nitida and E. globulus higher than bark samples of the studied species, supporting the idea suggesting that tree leaves can be used as a good indicator of heavy metals accumulation. A high and statistically significant correlation (p<.05) was found between Pb concentrations in the atmospheric dust and those in the leaves of both species throughout the two growing seasons, confirming that the main source of incorporated Pb is the atmospheric dust. Otherwise, the obtained results showed that F. nitida tree does not seem to be a good accumulator of Cu. According to the obtained results, F. nitida and E. globulus trees are more likely to capture cadmium and lead from air, so planting these trees in industrial areas with such atmospheric pollutants would be beneficial.
The study aimed too to explore the tolerance potential of these heavy metals (Cd, Pb and Cu) on the physiological alterations in E. globulus and F. nitida and to investigate the leaf features [leaf area (LA) and specific leaf area (SLA)] associated with the phytoremediation process. The findings may be useful for future surveillance as preliminary reference values for levels of heavy metals in urban and industrial settings. The results showed that heavy metals could inhibit the growth of plants including LA and SLA. The water content (WC) and photosynthetic pigments of E. globulus and F. nitida decreased with the increased concentration of metals. Contrary to chlorophylls (a) and (b), carotenoids and chlorophyll ratio (a/b) showed a significant increase with increasing metals concentration especially that of Cd and Cu. Proline content was relatively increased and soluble carbohydrate content decreased in plants with high metal accumulation. Eucalyptus showed better tolerance capacity for Cd, Pb and Cu when compared to Ficus. The ability of Eucalyptus to accumulate and tolerate metal stress makes this species a good candidate to recuperate heavy metals-contaminated conditions.
The study included morphological examination of both dust deposited on the leaves in the studied sites and the leaf itself to detect the level of harmful caused by theses pollutants. Studying the micromorphological characters was performed through the examination of Scanning electron microscope images of leaves and dust. The results showed significant variation in the macromorphological characters of leaves and dust present in the contaminated sites when compared with the reference site. Analysing diffraction x-ray patterns (XRD) of dust particles showed that the studied sites contain calcite and quartz.
The second part was related to biochar as soil amendment to enhance non-irrigated crop productivity in arid and semi-arid regions. Such amendments may either aim to improve the capacity of soil to retain moisture, or to enhance the capacity of plants to resist water deficits. The experiment was conducted in a greenhouse at the University of Toronto using two annual forb species: velvetleaf (Abutilon theophrasti), and lambsquarters (Chenopodium album) with the application of two types of biochar (sugar maple and conifer), and two treatments (well irrigation and drought). The study included the measurement of different ecophysiological parameters that test plant health and its ability to resist drought, such as: pigments content, chlorophyll fluorescence and leaf gas- exchange measurements. Soil properties were measured too, including pH, EC and soil moisture. The study proofed the ability of biochar to mitigate drought conditions.