A novel role of sulfate in promoting Mn phytoextraction efficiency and alleviating Mn stress in Polygonum lapathifolium Linn.

A hydroponic method was performed to explore the effects of sulfate supply on the growth, manganese (Mn) accumulation efficiency and Mn stress alleviation mechanisms of Polygonum lapathifolium Linn. Three Mn concentrations (1, 8 and 16 mmol L-1, representing low (Mn1), medium (Mn8) and high (Mn16) concentrations, respectively) were used. Three sulfate (S) levels (0, 200, and 400 µmol L-1, abbreviated as S0, S200 and S400, respectively) were applied for each Mn concentration. (1) The average biomass (g plant-1) of P. lapathifolium was ordered as Mn8 (6.36) > Mn1 (5.25) > Mn16 (4.16). Under Mn16 treatment, S addition increased (P < 0.05) biomass by 29.96% (S200) and 53.07% (S400) compared to that S0. The changes in the net photosynthetic rate and mean daily increase in biomass were generally consistent with the changes in biomass. (2) Mn accumulation efficiency (g plant-1) was ordered as Mn8 (99.66) > Mn16 (58.33) > Mn1 (27.38); and S addition increased (p < 0.05) plant Mn accumulation and Mn transport, especially under Mn16 treatment. (3) In general, antioxidant enzyme activities (AEAs) and malondialdehyde (MDA) in plant leaves were ordered in Mn16 > Mn8 > Mn1. Sulfate addition decreased (P < 0.05) AEAs and MDA under Mn16 treatment, while the changes were minor under Mn1 and Mn8 treatments. (4) Amino acid concentrations generally increased with increasing Mn concentration and S level. In summary, the medium Mn treatment promoted plant growth and Mn bioaccumulation; sulfate, especially at 400 µmol L-1 S, can effectively promote plant growth and Mn accumulation efficiency. The most suitable bioremediation strategy was Mn16 with 400 µmol L-1 S.

Hydrocotyle vulgaris L.: a new cadmium-tolerant landscape species and its physiological responses to cadmium exposure.

Landscape plants have both ecological and aesthetic value and may also represent ideal candidates for phytoremediation. In the present study, one round of hydroponic culture for 14 days with different cadmium (Cd) concentrations (0, 0.5, 1, and 2 mg L-1 Cd) was carried out to test whether Hydrocotyle vulgaris L. is a Cd-tolerant plant. Furthermore, physiological parameters, including pigment concentrations, photosynthesis, antioxidant enzyme activities (AEAs), and nutrient uptake, were also examined to determine the tolerance of H. vulgaris to Cd exposure. The results showed that H. vulgaris could grow normally under all Cd supply levels. The Cd removal efficiency reached 100% at Cd concentrations ≤1.0 mg L-1. The concentrations of Cd in roots and shoots increased (P < 0.05) with Cd supplementation. The maximum concentrations of Cd reached 26.4 and 118 mg kg-1 in shoots and roots, respectively. The translocation factor values were similar under all Cd treatments. The highest mean daily increase in biomass (MDIB) was obtained under 1 mg L-1 Cd exposure, which increased by 69.86% compared to that in the control, which may be due to the increased photosynthetic pigments, photosynthetic rate, and the consistent nutrient concentrations under this Cd level, as there were positive relationships between these parameters and MDIB. Moreover, the activities of AEA also generally explicated highest among all Cd levels. All these results indicate that the above physiological parameters play a positive role in promoting plant growth and alleviating Cd stress. In summary, H. vulgaris was verified as a potential Cd-tolerant plant, providing new information for Cd phytoremediation. Furthermore, given its extensive habitat distribution, this species might be tested for phytoremediation of contaminated soils in future work.