Elevated C[O.sub.2] improves root growth and cadmium accumulation in the hyperaccumulator Sedum alfredii

Aims This study examined the effect of elevated C[O.sub.2] on plant growth, root morphology and Cd accumulation in S. alfredii, and assessed the possibility of using elevated C[O.sub.2] as fertilizer to enhance phytoremediation efficiency of Cd-contaminated soil by S. alfredii. Methods Both soil pot culture and hydroponic experiments were carried out to characterize plant biomass, root morphological parameters, and cadmium uptake in S. alfredii grown under ambient (350 µL [L.sup.-1]) or elevated (800 µL [L.sup.-1]) C[O.sub.2]. Results Elevated C[O.sub.2] prompted the growth of S. alfredii, shoot and root biomass were increased by 24.6-36.7% and 35.0-52.1%, respectively, as compared with plants grown in ambient C[O.sub.2].After 10 days growth in medium containing 50 µM Cd under elevated C[O.sub.2], the development of lateral roots and root hairs were stimulated, additionally, root length, surface area, root volume and tip number were increased significantly, especially for the finest diameter roots. The total Cd uptake per pot was significantly greater under elevated C[O.sub.2] than under ambient C[O.sub.2]. After 60 d growth, Cd phytoextraction efficiency was increased significantly in the elevated C[O.sub.2] treatment. Conclusions Results suggested that the use of elevated C[O.sub.2] may be a useful way to improve phytoremediation efficiency of Cd-contaminated soil by S. alfredii. Keywords Cd uptake * Elevated C[O.sub.2] * Phytoextraction * Root morphology * S. alfredii