Morpho-physiological and biochemical insights into phytoremediation of lithium by sunn hemp (Crotalaria juncea L.) and napier grass (Cenchrus purpureus Schumach.)

Phytoremediation is a green and cost-effective strategy used to clean up metal pollutants from contaminated soils. Recently, non-crop species have gained attention for their ability to adapt to and thrive in contaminated environments, making them promising candidates for phytoextraction. However, their effectiveness in accumulating lithium (Li) is not well understood. This study explored the potential of sunn hemp (Crotalaria juncea L.) and napier grass (Cenchrus purpureus Schumach.) for phytoextraction of lithium a challenging and emerging soil contaminant under controlled greenhouse conditions. Inductively coupled plasma‒mass spectrometry (ICP‒MS) was used to measure uptake of lithium and compartmentalized in plant tissues at different contamination levels. Both sunn hemp and napier grass showed notable capacities for lithium uptake, demonstrating their potential for lithium phytoextraction. The accumulation pattern revealed significantly higher lithium concentrations in roots than in shoots, indicating limited translocation within these plant species. The highest lithium accumulation was recorded in the 1500 µM treatment group in the roots, reaching 7.37 mg/g DW (p < 0.001) in sunn hemp and 4.69 mg/g DW (p < 0.001) in napier grass. Lithium treatment led to alterations in growth (length and weight of shoots and roots and root architecture), photosynthetic efficiency, gas exchange, and various biochemical traits (total protein and proline contents). Biochemical analysis, including measurements of antioxidant enzyme activities, provided insight into how these plants mitigate lithium-induced oxidative stress. Markedly increased proline levels were detected in both species under lithium stress, suggesting an adaptive, protective mechanism against oxidative damage. The highest proline concentration was recorded in sunn hemp at 1000 µM Li (0.24 mg/g FW) (p < 0.01). In this study napier grass exhibited better phytoremediation potential compared to sunn hemp. This comprehensive study highlights the potential of integrating weeds into phytoextraction strategies for the remediation of lithium-contaminated soils. These findings enhance our understanding by use of weeds as effective agents for phytoextraction and sustainable soil remediation techniques and provide crucial insights for the development of weed-based phytoremediation approaches.