Evaluation of Sacred Lotus (Nelumbo nucifera Gaertn.) as an Alternative Crop for Phyto-remediation

Abstract

Lotus, Nelumbo nucifera, offers a wide diversity of uses as ornamental, edible and medicinal plant. An opportunity for growing lotus as a crop in Alabama also has the potential for phyto-remediation. Lotus was evaluated for remediation of trace elements focusing on manganese (Mn), organic compounds targeting s-metolachlor and filtering aquaculture waste water. Lotus was evaluated for filtering trace elements by establishing a base line for tissue composition and evaluating lotus capacity to grow in solutions with high levels of Mn (0, 5, 10, 15, or 50 mg/L). Increasing Mn concentrations in solution induced a linear increase in lotus Mn leaf concentrations. Hyper-accumulation of Al and Fe was detected in the rhizomes, while Na hyper-accumulated in the petioles, all without visible signs of toxicity. Mn treatments applied to lotus affected chlorophyll content. For example, chlorophyll a content increased linearly over time while chlorophyll b decreased. Radical scavenging activity (DPPH) did not change over time but correlated with total phenols content, showing a linear decrease after 6 weeks of treatment. Ascorbic acid levels increased in response to lower Mn concentrations but at 50 mg/L or higher Mn treatment level, ascorbic acid levels were reduced.

Lotus was evaluated for its potential as a phyto-remediator of organic compounds by growing plants in different concentrations of s-metolachlor. In seedlings, biomass accumulation was affected by the treatments. However, membrane integrity, respiration, and photosynthesis were not affected by the treatments. Mature plants did not show symptoms of toxicity but chlorophyll (Chl) changes in content were related to s-metolachlor concentrations (Chl a content increased while Chl b decreased). Potential s-metolachlor metabolites were found in rhizomes from treated seedlings. However, levels detected were too low to be identified. In addition, traces of s-metolachlor applied to seedlings were found in rhizomes, as well as, in leaves from treated mature plants. Lotus proved to be an effective phyto-remediator of nutrient run-off (NH ₄⁺, NO₃, P) and suspended solids from waste water from intense aquaculture systems.