Subcellular distribution and chemical speciation of lead in Panicum repens under different cultivation methods

Torpedo grass (Panicum repens) has ecological restoration advantages in polluted water-level-fluctuation zones in rivers, lakes, and water reservoirs, due to its strong ability to purify heavy metals and other pollutants and its strong adaptability to extreme drought-flooding conditions. Through three pot experiments with different lead treatments (T₁: hydroponic culture + 400 mg·L⁻¹ Pb; T₂: hydroponic culture + 800 mg·L⁻¹ Pb; T₃: soil culture + 400 mg·L⁻¹ Pb), the subcellular and chemical distribution characteristics of the root, stem, and leaf of torpedograss were investigated after 5, 15, and 25 days of treatment, in order to reveal the heavy metal tolerance mechanism and dynamic migration and transport rules of torpedograss under different concentrations of Pb stress and different cultivation methods. The migration rate from the roots to the shoots of P. repens increases significantly with prolonged stress duration (P < 0.05). The average Pb content of the roots under T₁, T₂, and T₃ treatments was 4745.85, 6732.63 and 276.00 mg·kg⁻¹, which is 66.20, 80.21 and 4.30 times the average Pb content in the leaves, respectively. Torpedograss mainly detoxifies Pb damage through the cell wall. The second most important component is the cellular state, followed by soluble components, with signi F1cant differences in the proportion of each subcellular fraction component (P < 0.05). The chemical state of Pb in the root and stem were mainly distributed in the less active HAc and HCl states, respectively. The distribution ratio of Pb in the leaves of torpedograss was not obvious, and the distribution of Pb in various chemical states tended to be balanced. The accumulation of Pb (T₁ and T₃) in the roots of torpedograss showed an inflection point at 15 d, with a significant increase from 5 days to 15 days (P < 0.05), followed by a slow decrease from 15 days to 25 days (P > 0.05). This indicates that the accumulation of Pb in the roots of torpedograss reached the absorption limit at 15 days, which may be due to the activation of a certain escape mechanism in the roots of torpedograss. Overall, the root Pb accumulation ability of torpedograss under pure hydroponic conditions is significantly greater than that under soil cultivation, making it an obvious advantage for purifying polluted riverbank deepwater areas.