Influence of (nano-)biochar-based fertilizer on rice plant growth and metal(oild) uptake under the co-exposure of cadmium and arsenic in a life-cycle greenhouse study

The low fertilizer utilization efficiency and metal(loid) contamination have become dual challenges that constrain the production of rice and thus food security. To address these issues, a life-cycle greenhouse study was conducted with rice (Oryza sativa) grown in soil co-contaminated with cadmium (Cd) and arsenic (As) and treated with several synthetic fertilizers. These fertilizers included regular fertilizers (F), biochar-based fertilizers (BF) and nano-biochar-based fertilizers (NBF), each formulated with varying nitrogen:phosphorus:potassium (N:P:K) ratios (I, II, and III). The results revealed a differential suppression of Cd (strongest under F-I, followed by NBF-III) and As (strongest under F-II, followed by NBF-I) in rice grains, attributable to disparities in their environmental chemistry, bioavailability, and plant-mediated uptake and translocation mechanisms. While BF enhanced catalase and alkaline phosphatase activities, NBF more effectively stimulated urease activity throughout the 0–10 cm layer and sucrase activity in the deeper 5–10 cm zone. Notably, NBF increased soil metabolic diversity under Cd and As stress while strengthening the genetic regulatory capacity and environmental adaptability of microbial communities. Furthermore, NBF dynamically regulated the migration of Cd and As into porewater, resulting in more stable and effective immobilization compared to BF and F treatments. These findings highlight that the application of biochar, particularly nano-biochar, for paddy soil remediation necessitates a contaminant-specific and nutrient-managed strategy. Tailoring both the biochar type and the accompanying N:P:K ratio is crucial for targeting the biogeochemical behavior of the dominant contaminant, thereby ensuring grain safety and supporting sustainable rice production. Graphic Abstract: (Figure presented.)