Evaluation of Elemental Composition of Avicennia marina and Associated Soil, Karachi Coast, Pakistan

Noor, N.; Shaukat, S.S., and Naseem, S., 2016. Evaluation of elemental composition of Avicennia marina and associated soil, Karachi coast, Pakistan. The present study evaluates the elemental composition of root, stems, and leaves of Avicennia marina and related soil samples. The scanning electron microscope–energy dispersive spectrometer (SEM-EDS) technique along with wet chemical analysis was used for the determination of elemental composition and their ratios in vegetative parts of A. marina. The SEM of soil samples displays clay minerals having platy structure and well-rounded quartz mineral. The EDS spectra of soil represented an O>Si>Al>Ca>Mg>Fe>Na>K>Cl>Ti trend. The Al and Si in spectra confirm the presence of clays, whereas Ti and Fe indicate Ti-bearing mineral (ilmenite). Soil textural study shows that the soil is loamy sand. The wet chemical analysis of all three parts, viz. root, stems, and leaves of A. marina, follow the Na+>K+>Ca2+>Mg2+ trend. Roots accumulate more K+ (X̄ 12.6%) than stems (X̄ 6.9%) and leaves (5.0%), whereas stems of A. marina showed highest concentration of Ca2+ (X̄ 6.03%). The correlation matrix displayed antipathetic relationship among Na+–Mg2+ (−0.911) and K+–Mg2+ (−0.84) in the stems. Leaves exhibit maximum Na+ and Mg2+ accumulation, whereas stems possess their minimum concentration. High Na concentrations in leaves indicate that A. marina is a salt-secretor mangrove and can be treated for phytoremediation of salt-affected lands. A strong negative relationship (−0.996) exists between K+ and Mg2+, whereas poor correlations were found among Na+ and other three macroelements (K+, Ca2+, and Mg2+) in leaves. The K+/Na+ ratio is in the order of root>stems>leaves, whereas Ca2+/Na+ and Mg2+/Na+ ratios in A. marina followed stems>root>leaves and leaves>root>stems trends respectively. The overall highest sodium bioconcentration factor is responsible for osmoregulation and water transport from soil to plant parts. The EDS elemental composition was compared with wet chemical analysis and found compatible with each other, with few exceptions. Elements exhibit a Na+>K+>Ca2+>Mg2+ trend through both techniques. EDS elemental mapping shows the distribution of elements in the stems.