[Effects of Biochar on the Physicochemical Properties of Wheat Contaminated by Polyethylene Microplastics]

The aim of this study was to investigate the physiological and ecological effects and mechanisms of corn straw biochar （CSB） on polyethylene microplastics （PE-MPs） contamination in wheat-soil systems， identify the main controlling factors， and thus to provide insights for remediating farmland microplastic pollution. A wheat soil pot experiment was conducted to investigate the effects and remediation efficiency of CSB （0.0%， 0.5%， 1.0%， and 3.0%） on the growth and development， photothermal physiology， leaf antioxidant enzyme activity， and soil enzyme activity of wheat under PE-MPs （0.0%， 0.5%， 1.0%， and 5.0%， particle sizes 10 μm， 100 μm） pollution. Meanwhile， a partial least square （PLS） regression model was used to quantitatively analyze the relationships between various physicochemical properties and the fresh weight， dry weight， and growth indices of winter wheat， thereby identifying key controlling factors. The results indicate that PE-MPs contamination （both particle sizes） exhibited inhibitory effects on wheat growth， development， and physicochemical properties， while CSB application effectively mitigated these negative stress impacts. Compared to that in the PE-MPs 5.0% × CSB 0.0% treatment， CSB amendment increased plant height， leaf area， and aboveground biomass of wheat by averages of 11.70%， 21.92%， and 44.63%， respectively. Single PE-MPs contamination significantly increased canopy temperature while reducing leaf thickness and photosynthetic efficiency in wheat， whereas CSB amendment demonstrated significant remediation and mitigation effects. Furthermore， the finer polyethylene microplastics （10 μm PE-MPs） demonstrated significantly stronger inhibition across the measured physiological parameters compared to that of coarser fractions （100 μm）. CSB exhibited superior remediation efficacy in finer particle treatments， with 10 μm PE-MPs primarily impairing photochemical activity （quantified by F_v/F₀， maxim μm quant μm efficiency of PSII）， while 100 μm particles predominantly influenced net photosynthetic rate （P_n） regulation. PE-MPs contamination significantly enhanced the activities of superoxide dismutase （SOD）， catalase （CAT）， and peroxidase （POD） in wheat leaves while reducing soil urease （S-URE）， acid phosphatase （S-ACP）， and dehydrogenase （S-DHA） activities. After the addition of CSB， leaf enzyme activities decreased to varying degrees， while soil enzyme activities were promoted to different extents. CSB exhibited significantly higher restoration efficiency in 10 μm PE-MP-contaminated soils. PLS results revealed that under co-exposure of CSB and PE-MPs， the key controlling factors for fresh weight and dry weight changes in wheat were： F_v/F₀ （10 μm PE-MPs） for fresh weight， net photosynthetic rate （P_n） （100 μm PE-MPs） for fresh weight， and F_v/F₀ （100 μm PE-MPs） for dry weight. These findings provide a theoretical foundation and actionable insights for elucidating the interactive physiological-ecological mechanisms between CSB and PE-MPs in wheat systems， thus advancing the development of efficient and safe pollution control strategies.