Salt ions accumulation and distribution characteristics of pioneer plant species at a bauxite residue disposal area, China

Bauxite residue disposal areas (BRDAs) are physically degraded and hostile to plant growth. Nevertheless, natural plant colonization was observed in an abandoned BRDA in Central China. The pioneer plant species at the disposal area were identified, whilst distribution characteristics of salt ions such as Na+, K+, and Ca2+ in plant tissues and rhizosphere residues were investigated. The mean concentration of exchangeable Na+ in the rhizosphere soils was 19.5 cmol/kg, which suggested that these pioneer plants had relatively high salinity resistance. Sodium content varied from 0.84 cmol/kg (Digitaria sanguinalis) to 39.7 cmol/kg (Kochia scoparia), whilst K to Na ratio varied from 0.71 (Myricaria bracteata) to 32.39 (Digitaria sanguinalis) in the shoots, which demonstrated that the salinity tolerance mechanisms of these pioneer species differed significantly. Accumulation factors of Na+ in local plant species ranged from 0.04 (D. sanguinalis) to 3.29 (M. bracteata), whilst the translocation factor varied from 0.13 (D. sanguinalis) to 2.92 (M. bracteata). The results suggested that four pioneer plant species including K. scoparia, M. bracteate, Cynodon dactylon and D. sanguinalis could be suitable for revegetation at other disposal areas.