Abstract
The effects of different concentrations of Zn on growth of an aquatic macrophyte, Ipomoea aquatica Forsk. were studied. Fresh weight, dry weight, shoot length, root length, number of nodes, development of leaves, and chlorophyll and carotene contents were the different growth parameters considered. Toxicity symptoms like browning and decaying of roots could be observed in plants treated at 22.7 mg L-1 Zn as early as 3rd day of experiment while yellowing of older leaves appeared during the later period of exposure. High concentration of Zn (12.71 – 22.7 mg L-1) significantly inhibited the growth of plant while lower Zn concentrations up to 4.09 mg L-1 enhanced its growth. However, at 7.26 mg L-1 Zn the chlorophyll as well as total carotene content in leaf of I. aquatica were significantly reduced from that in control on 5th day of exposure and subsequently the reduction was observed in lower concentrations. Thus, I. aquatica can be employed in biomonitoring of Zn polluted aquatic ecosystems using root browning, root and shoot growth inhibition, and chlorophyll and total carotene contents as sensitive biomarkers.
Highlights
Natural environment, the aquatic ecosystem is being disturbed by anthropogenic activities with rise in industrialization and urbanization
At the termination of the experiment on 15th day all control and Zntreated plants were removed, washed with distilled water, and softly blotted to remove excess water before fresh weight of the plants, their root length and lateral roots, and leaf area were measured. This was followed by drying in hot air oven at 60 0C till constant weight. Other growth parameters such as shoot length, new leaves, and number of nodes were measured at 3 day intervals.The percentage of primary roots bearing lateral roots (PRL %), and the ratio of lateral roots (LR) to the number of primary roots bearing lateral roots (PRL) was calculated
Eichhornia crassipes when exposed to 20 mg L-1 Zn did not show any morphological symptom of toxicity[31]
Summary
The aquatic ecosystem is being disturbed by anthropogenic activities with rise in industrialization and urbanization. Its concentration in various Indian aquatic ecosystems has reached alarming levels as reported by a number of scientific studies[4,6,7,8,9]. The growing concern in environmental aspects as well as the narrow window between its essentiality and toxicity[16] has generated interest in studying its effects on aquatic plants which play an important role in ecosystem functioning. It is reported to be grown in other parts of the world like Africa, Australia and United States of America (Austin, 2007)[18] It is perennial and mostly grows in moist soil, inundated floodplains, ditches, ponds, canals and sluggish rivers[19] and easy to cultivate due to its ability to proliferate by fragmentation, and produce adventitious roots and lateral branches that bear flowers and leaves, from its nodes[20]. This study was, taken up to understand and assess the toxic effects of Zn on this aquatic macrophyte
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