Rhizosphere characteristics of phytostabilizer Athyrium wardii (Hook.) involved in Cd and Pb accumulation

Soil contamination with Cd and Pb shows interactive effects on rhizosphere microenvironment and further uptake of Cd and Pb by plants. Thus, the rhizosphere characteristics of the mining ecotype (ME) and non-mining ecotype (NME) of Athyrium wardii in response to Cd and Pb was investigated through a pot experiment in this study. Compared with Cd or Pb alone, the contamination of Cd and Pb inhibited the growth of the two ecotypes of A. wardii, and ME presented lower decrease of 56.22% and 55.07% for above-ground part biomass than NME. The combination of Cd and Pb promoted Cd accumulation both in above-ground and under-ground parts of ME, as well as Pb accumulation in under-ground parts of ME, with the increase of 92.68%, 102.77% and 35.87%, respectively. As a result, increased bioaccumulation coefficients (BCF) for Cd and Pb and decreased translocation factors (TF) for Pb of ME were observed when exposed Cd and Pb. ME presented much greater BCF values for Cd and Pb, and much lower TF values for Cd and Pb than NME. The rhizosphere soil pH of ME with the exposure of Cd and Pb reduced by 0.12-0.13 units compared with single Cd or Pb. The dissolved organic carbon (DOC) concentrations in rhizosphere soils of ME exposed to Cd and Pb increased in comparison with single Cd or Pb, and ME showed greater increase (53.31-59.00%) than NME. These suggested that pH reduction and exudation of greater amounts of DOC may have contributed to the promotion of Cd and Pb accumulation in ME. In addition, the combination of Cd and Pb inhibited soil microbial biomass carbon (MBC) and soil respiration (SR) of A. wardii compared with Cd or Pb alone. However, greater MBC and SR, and lower metabolic quotients were found in rhizosphere soils of ME when exposed to Cd and Pb. ME showed better soil biophysical conditions in rhizosphere soils when exposed to Cd and Pb. These improvements presented great benefit for ME to phytostabilize soils co-contaminated with Cd and Pb.