Suitable light combinations enhance cadmium accumulation in Bidens pilosa L. by regulating the soil microbial communities

Light is one of the natural resources greatly influencing plant growth, and light regulation has been recently considered one of the effective means of enhancing phytoremediation. In this study, monochromatic (red, blue, green), bichromatic (red and blue light combinations at different ratios), and trichromatic (red, blue, and green light combinations at different ratios) lights were applied at the same intensity (100 +/- 5 mu mol m(-2) s(-1)) to enhance cadmium (Cd) accumulation in Bidens pilosa L. Compared with the control (fluorescent light), the translocation factor (TF), bioconcentration factor (BCF), and total metal extraction (TE) values of the plant were increased by 13.47-99.24%, 5.33-39.64%, and 20.51-109.62%, respectively, under light-emitting diode (LED) irradiation. The highest BCF and TE values were observed in plants under R(20)B(70)G(10) (20% red, 70% blue, and 10% green light) irradiation, whereas a higher TF value was detected in plants under the condition of R50B50 (50% red and 50% blue light) and R(20)B(70)G(10). Hierarchical clustering and heatmap analysis showed that trichromatic light influenced plant growth, photosynthesis, antioxidant enzyme activity, and soluble protein contents more than bichromatic and monochromatic lights. Additionally, the abundances of rhizosphere microbes and plant growth-promoting rhizobacteria, such as Lysobacter and Ramlibacter, were significantly higher under LED irradiation, along with enhanced soil enzyme activity. Our findings suggested that the R(20)B(70)G(10) trichromatic light efficiently induces plant Cd extraction and can significantly improve the phytoremediation of Cd-contaminated soils by Bidens pilosa L.