Identification of indicators of giant reed (Arundo donax L.) ecotypes for phytoremediation of metal-contaminated soil in a non-ferrous mining and smelting area in southern China

An investigation of giant reed (Arundo donax L.) in a non-ferrous mining and smelting area in southern China was carried out to select indicators to identify ecotypes suitable for phytoremediation in terms of their morphology, biochemistry, and sustainability. Giant reed populations were found to be able to survive in extremely contaminated soils in the studied non-ferrous mining and smelting area of southern China, with soil pH ranging from 2.9 to 9.59, cadmium (Cd) content of up to 525 mg/kg, and lead (Pb) content of up to 57194 mg/kg. The giant reed population at Hunan (HN), with a soil Cd content of up to 2.3 mg/kg, and that at Yunnan (YN), with a soil Pb content of up to 33.8 mg/kg, were selected as suitable sources of ecotypes with high phytoremediation potential in the studied area's soil. The leaf area, height, and photosynthetic pigment content of plants of the HN and YN ecotypes were not significantly affected by metal contamination compared to some other populations, while the malondialdehyde (MDA) content of giant reeds was increased by up to 30 mu mol/g by Cd and Pb contamination. In the results of a principal component analysis (PCA) of all the giant reed indicators assessed, the different giant reed ecotypes were most clearly identified by the biochemical and morphological indicators included in principal component 2. The biochemical and morphological indicators of giant reed, including their leaf area, height, and content of malondialdehyde (MDA) and chlorophyll a could thus be regarded as decisive indicators for the identification of giant reed ecotypes, which was confirmed by a further detrended correspondence analysis (DCA) and redundancy analysis (RDA). The irregular granular excretion was also a reliable indicator of giant reed ecotypes with phytoremediation potential, especially of the solid ecotypes examined using a scanning electron microscope (SEM). The identified indicators were consistent with the finding that these giant reed ecotypes could be pseudo-metallophytes. In addition, the level of genetic variation was not significantly reduced by heavy metal accumulation, identifying a sustainability of a giant reed population. Considering the similarity in the proportion of cellulose content, the giant reed could also be widely used as bioenergy crop producing abundant cellulose for the economical phytoremediation of large areas of non-ferrous contaminated soil. The methods and conclusions of this study could also serve as a reference and source of guidance for the identification of indicators of other plants with promising phytoremediation potential.