Growth and Phytostabilization Potential of Willow under Rare Earth Elements Exposure in Floating Treatment Wetlands

Abstract

Phytoremediation of contaminated freshwater bodies with rare earth elements (REEs) is a promising nature-based solution, but it is rarely studied. Here, we studied how efficiently willow ( Salix schwerinii: SS ) and cultivar (Klara: KL) purify water and react to three combined doses of REEs. SS and KL were subjected to increasing combined doses of REEs, specifically lanthanum (La) and neodymium (Nd), for 8 weeks in floating treatment wetlands (FTWs). The treatments included: T0 (tap water without REEs), T1 (10 µM La + 10 µM Nd), T2 (20 µM La + 20 µM Nd), and T3 (40 µM La + 40 µM Nd). The study aimed to evaluate how La and Nd affect willow growth, including height, dry biomass, and tolerance index, as well as their uptake and translocation within the roots, stems and leaves. Results showed that willow height increased over time, with significant biomass development and a noticeable allocation to stem biomass under REEs exposure. Height and biomass tolerance indices indicated that SS and KL exhibited high tolerance to REEs. The findings revealed the highest accumulation of La (25,252 μg plant −1 ) and Nd (18,252 μg plant −1 ) in the roots of SS in treatment T3. KL also showed the highest accumulation of La (16,153 μg plant −1 ) and Nd (13,209 μg plant −1 ) in roots, but in treatment T2. Moreover, SS and KL demonstrated increased translocation of La and Nd, particularly from the water solution to the roots, with minimal translocation to the leaves and stems. In SS, La and Nd removal efficiencies ranged from 56–95% and 40–74%, respectively. For KL, La removal varied from 22–90%, while Nd removal ranged from 21–68%. A considerable accumulation of nutrients such as P, K, Mg, and Ca in the willow tissues was also observed. Further research is needed to evaluate the long-term removal and recovery of REEs by willow and other perennial plants, with a primary focus on environmental factors and design of FTWs which may influence the uptake and translocation of REEs in plants.

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