Preliminary indications on the suitability of Cannabis sativa L. plants to tolerate and phytoaccumulate Lithium: implications for phytotechnologies

Lithium (Li), an alkali metal and the least dense metal (0.534 g/cm3), has received particular attention due to its increasing demand for the production of Li-ion batteries. Concerns have been raised about the impact on biota of Li mining residues and improper disposal of Li containing materials [1]. Measures must be taken to mitigate these negative effects, and nature-based technologies could be of interest for their environmental and economic sustainability. Plant-lithium interactions have recently been studied to evaluate both the metal toxicity [2] and the plant ability for phytoaccumulation (phytomining). To get an insight on both these issues, a preliminary ecotoxicity assay on Lepidium sativum L. was carried out to choose the Li concentrations to be tested. Then, two proofs of concept under lab conditions were conducted, targeting the suitability of Cannabis sativa L. to tolerate and bioaccumulate Li added in the growth medium. For this purpose, in vitro and hydroponic trials were carried out. Regarding the former, micro-shoots of C. sativa were exposed for two weeks, under controlled microenvironmental conditions, to 0 (control), 50 mg/L, 150 mg/L, 300 mg/L LiCl supplied by the Murashige and Skoog growth medium. In the latter, three-week-old plantlets were grown for 10 days in growth chamber in nutrient solution containing 0 (control), 50 mg/L, 150 mg/L, 300 mg/L LiCl. At the end of the two experiments, plants were analysed for morpho-physiological and ionomic traits by evaluating biometric parameters, pigment content, photosynthetic performances (chlorophyll fluorescence imaging analysis), macro and micronutrients concentration and Li accumulation in the organs. Results highlighted the ability of hemp plants to absorb, accumulate and translocate Li while tolerating it at the lowest concentration tested. Alteration of photosynthetic performances and ion content were observed at the highest Li concentration assayed. These preliminary investigations suggest that hemp plants have potential for use in remediation and metal biorecovery strategies in Li-contaminated substrates. However, further trials in real conditions are necessary to confirm these findings. References: [1] R.B. Kaunda, Journal of Energy & Natural Resources Law 2020, 38, 237-244. [2] R. Kastori, et al., Contemporary Agriculture 2022, 71, 226-239.