Physiological and biochemical responses of duckweed under heavy metal stress: Insights from chlorophyll, nutrient dynamics and SEM analysis

Abstract

Heavy metal contamination in aquatic ecosystems poses a significant threat to plant health
and environmental sustainability. The present study investigates the physiological and
biochemical responses of two duckweed species, Lemna minor and Lemna gibba, under
cadmium (Cd) and chromium (Cr) stress. Plants were exposed to varying concentrations (1–
9 mg/L) of Cd and Cr for 7 and 15 days, and their responses were evaluated through
chlorophyll analysis, nutrient profiling, and scanning electron microscopy coupled with
energy dispersive X-ray (SEM-EDX) analysis. A concentration-dependent decline in
chlorophyll a, chlorophyll b, and total chlorophyll content was observed, indicating inhibition
of photosynthetic activity under heavy metal stress. Nutrient analysis revealed significant
imbalances in essential macro- and micronutrients, including potassium (K), calcium (Ca),
sodium (Na), iron (Fe), zinc (Zn), manganese (Mn), magnesium (Mg), and copper (Cu),
suggesting disruption of nutrient uptake and metabolic processes. SEM analysis demonstrated
pronounced structural damage in treated plants, while EDX confirmed the accumulation of
Cd and Cr within plant tissues. Comparative analysis indicated that Lemna minor exhibited
relatively higher tolerance, whereas Lemna gibba showed greater sensitivity to metal stress.
Overall, the study highlights the integrated impact of heavy metals on plant physiology,
linking chlorophyll degradation, nutrient imbalance, and structural alterations as key
indicators of stress. These findings provide valuable insights into plant stress mechanisms and
support the potential use of duckweed species as bioindicators for monitoring heavy metal
pollution in aquatic environments.