Effects of flooding depth on metal(loid) absorption and physiological characteristics of Phragmites australis in acid mine drainage phytoremediation

To solve the problem of determining which flooding depth is suitable for the process of phytoremediation of acid mining drainages (AMDs), we compared the responses of reed (Phragmites australis), an amphibious plant widely used in phytoremediation, to different flooding depths. In the greenhouse, synthetic AMD was set to four flooding depths (5, 15, 35 and 55 cm); the culture medium consisted of non-acidified tailings; and the growth, trace element contents in different organs and physiological indexes of the reeds were measured 90 days after planting. The results showed that compared with the control group without reeds, the reeds increased the pH value of AMD. More than 5 cm of flooding inhibited the activity of roots and promoted adventitious roots. The plant height and tiller number were significantly increased by 35 cm of flooding. In addition, the levels of trace element absorption of different organs were different at various depths. In general, deeper flooding promoted the absorption of trace elements (except As), and most of these trace elements accumulated in the roots. Through the calculation of the translocation index (TI), it was found that Mn had the highest value and increased with depth. The physiological effects of flooding on different organs were often diverse at various depths, but the leaf blades maintained high enzyme activity and proline content, while the leaf sheaths contained the greatest amount of soluble protein. Therefore, the 35 cm depth of flooding is reasonable for the phytoremediation of AMD to avoid effects on plant growth from the water depth and/or low pH. (C) 2021 Elsevier B.V. All rights reserved.