Brassica juncea has great application potential in phytoremediation of cadmium (Cd)-contaminated soil because of its excellent Cd accumulating and high biomass. In this study, we compared the effects of Cd under 48 h and 7 d stress in roots of Brassica juncea using metabolite profiling. The results showed that many metabolic pathways and metabolites in Brassica juncea roots were altered significantly in response to Cd stress. We found that significant differences in levels of amino acids, organic acids, carbohydrates, lipids, flavonoids, alkaloids, and indoles were induced by Cd stress at different times, which played a pivotal role in the adaptation of Brassica juncea roots to Cd stress. Meanwhile, Brassica juncea roots could resist 48 h Cd stress by regulating the biosynthesis of amino acids, linoleic acid metabolism, aminoacyl-tRNA biosynthesis, glycerophospholipid metabolism, ABC transporters, arginine biosynthesis, valine, leucine and isoleucine biosynthesis, and alpha-linolenic acid metabolism; however, they regulated alpha-linolenic acid metabolism, glycerophospholipid metabolism, ABC transporters, and linoleic acid metabolism to resist 7 d Cd stress. A metabolomic expedition to the response of Brassica juncea to Cd stress will help to comprehend its tolerance and accumulation mechanisms of Cd.

Sugarcane smut, caused by the fungal pathogen Sporisorium scitamineum, leads to significant economic losses in the global sugarcane industry. Bio-organic fertilizers (BF) offer a promising and sustainable strategy to mitigate smut incidence and enhance sugarcane growth. While the application of BF is known to modulate root exudates and rhizosphere microbial community structure, thereby promoting disease resistance, the precise mechanisms underpinning BF-mediated suppression of sugarcane smut remain largely unclear. This study investigated the microbiological mechanisms of smut suppression using a pot experiment, comparing a novel BF treatment (composted substrate enriched with Bacillus subtilis, Bacillus altitudinis, Bacillus cereus, Trichoderma harzianum, and Trichoderma longibrachiatum, biochar, and calcium carbonate) with a control receiving only conventional organic fertilizer. BF application significantly increased plant height (by 95.2%), dry weight (137.5%), fresh weight (253.3%), and sugar content (43.1%) relative to the control. Furthermore, the BF treatment enhanced catalase activity by 167.8% and peroxidase activity by 102.3% in sugarcane leaves, while the control effectiveness against the incidence of smut disease reached 88.0%. Analysis of the rhizosphere microbiome revealed that BF application significantly altered microbial alpha- and beta-diversity. Specifically, the BF treatment notably enriched beneficial genera such as Pseudomonas and Meyerozyma. Beta-diversity analysis revealed distinct microbial community structures in BF-treated rhizosphere soil compared to the control. Correlation and random forest analyses identified Pseudomonas and Meyerozyma as key taxa that were positively associated with sugarcane growth parameters and negatively correlated with smut incidence. These findings elucidate the dual role of this novel BF in enhancing sugarcane growth and suppressing smut incidence through the strategic reshaping of the rhizosphere microbiome.