Biochar and arbuscular mycorrhizal fungi promote rapid-cycling Brassica napus growth under cadmium stress.

PURPOSE

To explore the mechanisms of tolerance of Brassica napus to ultra-high concentration cadmium pollution and the synergistic effects of biochar (BC) and Arbuscular mycorrhizal fungi (AMF) on plant growth under cadmium (Cd) stress.

RESULTS

The application of 5 % BC and inoculation with 10 g AMF significantly promoted the growth and development of B. napus. The combined application of BC and AMF (BC1A and BC2A) was better than the single application. At the Cd 200 mg/kg level, BC1A increased the fresh weight and Cd content of the above-ground parts of B. napus by 35.5 % and decreased by 21.20 %. The SOD and POD activities increased by 30.63 % and 73.37 %. The MDA and HO contents decreased by 40.8 % and 69.99 %, soluble sugar content increased by 37.96 %. At the Cd 300 mg/kg level, BC1A increased the fresh weight and Cd content of the above-ground parts of B. napus by 32.8 % and decreased by 15.99 %. The SOD and POD activities increased by 39.06 % and 93.56 %. The MDA and HO contents decreased by 28.39 % and 72.45 %, and the soluble sugar content increased by 21.16 %. Overall, both BC and AMF treatments alone or in combination (BC1A) were able to alleviate Cd stress and promote plant growth, with the combination of biochar and AMF being the most effective. Furthermore, transcriptome analyses indicated that BC may improve cadmium resistance in B. napus by significantly up-regulating the expression of genes related to peroxidase, photosynthesis, and plant MAPK signaling pathways. AMF may alleviate the toxicity of Cd stress on B. napus by up-regulating the expression of genes related to peroxisomes, phytohormone signaling, and carotenoid biosynthesis. The results of the study will provide support for ecological restoration technology in extremely heavy metal-polluted environments and provide some reference for the application and popularization of BC and AMF conjugation technology.