Impacts of Tobacco Stalk Biochar Remediation in Microplastic-Contaminated Soil on Early Rice Growth Indicators and Soil Quality

Microplastic pollution in farmland soils has emerged as a global concern due to its potential to degrade soil health, inhibit crop growth, and enter the food chain. However, effective and environmentally friendly remediation strategies remain limited, particularly regarding the use of biochar to mitigate polyethylene microplastic (PE-MP) stress in agroecosystems. This study investigates whether tobacco stalk biochar (TSB) can alleviate PE-MPs stress in rice seedlings. A two-factor pot experiment was conducted to systematically analyze the responses of soil physicochemical properties, rice growth indicators, and antioxidant enzyme activities to the combined application of varying concentrations of PE-MPs (0, 0.5%, 1%, and 2% (w/w)) and TSB (0, 3%, 6%, and 9% (w/w)). The results show that TSB significantly increased soil pH and organic matter content, effectively mitigating the decline in available nitrogen, phosphorus, and potassium caused by PE-MPs (e.g., under the M3B3 treatment, available nitrogen and phosphorus contents increased by 68.7% and 226%, respectively, compared with those under the M3B0 treatment). Under low-concentration PE-MP (0.5%) stress, an appropriate amount of TSB (3%) resulted in the highest rice germination rate, vigor index, and stress tolerance index, while significantly inducing the activities of superoxide dismutase (SOD) and catalase (CAT) to alleviate oxidative damage. However, high-concentration combinations of TSB and PE-MPs exhibited an antagonistic effect. In conclusion, tobacco stalk biochar can synergistically mitigate microplastic stress on rice through multiple pathways, with its remediation effects exhibiting significant dose dependence and interactive complexity. These findings provide a theoretical and technical basis for the ecological remediation of microplastic pollution in farmland.