PHENOTYPIC AND HISTOLOGICAL PLASTICITY OF EICHHORNIA CRASSIPES IN TWO POLLUTED AQUATIC HABITATS - AN INDICATOR OF INVASIVE ADAPTATION

Abstract

Present study reports the results of a comparative evaluation of the morphological and anatomical variations exhibited by the alien invasive-Eichhornia crassipes (Mart.) Solms in two polluted water bodies in Trivandrum city in relation to its normal growth responses in a non-polluted fresh water pond. The water samples from the two experimental sitesParvathy Puthanar and Veli Lake were analysed for their physicochemical parameters. The morpho-anatomical variability in response to physico-chemical differences has been interpreted to elucidate the invasive adaptations of the species. Water samples collected were compared for BOD, COD, pH, alkalinity, carbonates and bicarbonates. Morphological variations between plant samples were analysed for parameters such as plant size, shoot and root length, root hair proliferation, colouration of roots, bulb girth, petiole length, discolouration of bulb and leaves. Transverse sections of lamina, petioles and roots were compared for variability in anatomical parameters. Water samples from Parvathy Puthanar exhibited higher BOD and COD. The pH of water samples were detected as slightly acidic in Parvathy Puthanar and above neutral in Veli Lake. The adaptive features of the plant included decline in root/shoot ratio, reduced size of petiolar bulb and petiole elongation, reduction in number of root length and lateral branches, development of chlorotic and necrotic patches during salinity stress in Veli Lake. Histological evaluation of plant parts concluded increase in stomatal indices (8.69-29.1%), variations in stomatal aperture size, enhanced epidermal and mesophyll thickness, increment of leaf vascular bundles, reduced air spaces in aerenchyma of petiole and roots.