Biochar mitigates Cr toxicity by improving soil properties, promoting plant growth, and reducing Cr accumulation in tropical bamboo Dendrocalamus brandisii

Chromium (Cr) contamination in the soil can severely hinder plant growth. Dendrocalamus brandisii , an evergreen clumping bamboo used for both bamboo timber and shoots, is affected by Cr within its primary distribution range, but the biochar can reduce the absorption of Cr by plants. In this study, we exposed D. brandisii to simulated Cr stress to analyze its physiological responses, and explored the effects of different types biochar on Cr accumulation in seedlings. The results showed that Cr bioaccumulates in D. brandisii lead to cellular damage and oxidative stress. DEGs encoding osmotic regulators, antioxidant enzymes, ion transporters, and transcription factors enhance tolerance by limiting Cr uptake and transport. After 5 % biochar application, the soil Cr significantly decreased, and the growth of seedlings was improved, with corn straw biochar exhibiting the most remarkable effect in reducing Cr uptake (20.19 %). More intriguingly, biochar changed the microbial community stability in addition to increasing soil nutrients. Collectively, D. brandisii activates its antioxidant defense machinery and key signaling pathways in response to Cr, while biochar application significantly reduces Cr uptake and accumulation in seedlings through modifying soil properties and influencing the microbial community. These findings provide foundational theoretical support for dealing with heavy metal contamination in bamboo cultivation. • Cr contamination caused physiological damage and oxidative stress in D. brandisii . • Transcriptomic analysis revealed key genes involved in Cr stress tolerance mechanisms. • Application of 5 % biochar decreased roots absorption of Cr. • Biochar has altered the richness and stability within the rhizosphere microbial.