Recruitment of specific microbes through exudates affects cadmium activation and accumulation in Brassica napus

Exploration of the mechanisms of cadmium (Cd) activation mediated by the rhizosphere process is important to advance our understanding of Cd accumulation in plants. In this study, two oilseed rape cultivars (L338, L351) with varied Cd accumulation traits were applied and the responses of their rhizosphere ecology to Cd stress were investigated by metabolome and microbiome. The results showed that shoot Cd accumulations in L338 accounted for 54.16% and 64.76% of those in L351 under low and high Cd contamination, respectively. Moreover, the cultivars response of rhizosphere process reflected that the lower pH and higher Cd mobility were assigned to the characters of L351, which were induced by the secretion of carboxylic acid (e.g. Acetaminophen cysteine, N-Fructosyl alliin) and the enrichment of bacterial taxa with the capacities of Cd resistant and acti-vation (e.g. Sphingomonas, Flavobacterium, Neorhizobium, Altererythrobacter). Conclusively, the varied Cd accu-mulation traits of two oilseed rape cultivars were not only derived from the Cd transfer ability, it would be ascribed to Cd mobility regulated by rhizosphere processes as well. The results provide baseline data and a new perspective on the cultivar response of Cd accumulation, thus maintaining cleaner production of oilseed rape.

Automated summary

The exploration of cadmium activation mechanisms mediated by the rhizosphere process is crucial for understanding the accumulation of cadmium in plants. This study investigated the responses of two oilseed rape cultivars with different cadmium accumulation traits to cadmium stress using metabolome and microbiome analyses. The results revealed that the differences in shoot cadmium accumulation between the two cultivars were attributed to the rhizosphere processes, which were influenced by pH, cadmium mobility, and the secretion of certain organic acids. Bacterial taxa with cadmium-resistant and activation capacities were also found to be enriched in the rhizosphere of one of the cultivars. These findings provide important insights into the cultivar response to cadmium accumulation and can contribute to the cleaner production of oilseed rape.