Alleviating chromium (Cr) toxicity in maize (Zea mays L.) using oak wood biochar and carbon nanoparticles: impacts on growth, physiology, and stress responses

The rising demand for food production necessitates innovative and sustainable agricultural practices, particularly in soils contaminated with heavy metals such as chromium (Cr). Oak wood biochar (OW-BC) and carbon nanoparticles (CNPs) have emerged as promising amendments for enhancing soil quality and plant health while mitigating Cr stress. This study explored the effect of OW-BC and CNPs on maize (Zea mays L.) growth, nutrient concentration, and soil enzymes under Cr stress (50 mg kg−1 Cr as total Cr) in a pot experiment. Results showed that OW-BC and CNP treatments increased shoot fresh weight by 30.2% and 28.0% without Cr stress, and by 34.1% and 28.4% under Cr stress, respectively, relative to the Cr treatment. Under Cr stress, OW-BC and CNPs improved shoot P concentration by 23.6% and 71.1%, respectively, relative to the Cr treatment, though shoot K concentration was not restored to control levels. Under Cr stress, both OW-BC and CNPs exhibited statistically non-significant, but numerically lower shoot Cr concentrations (by 8.1% and 10.0% compared with the Cr-alone treatment, respectively), as well as similar numerical increases in biomass (34.1% vs. 28.4%). The results in this study indicate that OW-BC and CNPs act as good soil conditioners and plant protectants to enhance plant tolerance to Cr toxicity and support sustainable crop production. Schematic illustration of the potential mechanisms by which biochar and carbon nanoparticles improve soil health, reduce chromium (Cr) bioavailability, and promote plant growth under Cr stress. This study demonstrated that OW-BC and CNPs differentially modulated Cr accumulation and phytotoxicity in maize, reducing shoot Cr concentration by up to 8.1% and increasing shoot P concentration by up to 71.1% under Cr stress. These findings provide a mechanistic basis for recommending OW-BC and CNPs as affordable amendments for Cr-contaminated soils, with field-scale trials needed to confirm long-term efficacy. Oak Biochar (OW-BC) and carbon nanoparticles (CNPs) decreased Cr accumulation in maize shoots by 8.1% and 10.0%, respectively, under Cr stress.Under 50 mg kg−1 Cr stress, OW-BC enhanced phosphorus concentration more than CNPs in both roots and shoots.OW-BC and CNPs reduced Cr accumulation and improved nutrient concentration in Cr-contaminated soils. Oak Biochar (OW-BC) and carbon nanoparticles (CNPs) decreased Cr accumulation in maize shoots by 8.1% and 10.0%, respectively, under Cr stress. Under 50 mg kg−1 Cr stress, OW-BC enhanced phosphorus concentration more than CNPs in both roots and shoots. OW-BC and CNPs reduced Cr accumulation and improved nutrient concentration in Cr-contaminated soils.