The incorporation of organic amendments, such as food waste (FW) and biochar, into soil is an established agronomic practice known for enhancing soil fertility and improving overall soil health. However, the individual and combined effects of FW and biochar on soil properties in microplastic (MP)-contaminated soil–plant systems remain poorly understood. To address this knowledge gap, we conducted a field experiment to investigate the individual and combined effects of polystyrene MPs, FW, and FW-derived biochar on soil properties and lettuce growth. Soil chemical properties were unaffected by the addition of MPs. However, the application of FW and biochar increased the soil pH, with the highest pH (8.2) observed in the combined treatment of biochar and MPs. Despite the presence of MPs, FW application resulted in notable increases in soil electrical conductivity (EC; 2.04 dS m−1), available nitrogen (NO3−–N: 325.5 mg kg−1, NH4+–N: 105.2 mg kg−1), available phosphorus (88.4 mg kg−1), and total exchangeable cations (18.6 cmol(+) kg−1). However, these values decreased after lettuce cultivation. In soil cultivated with lettuce, the coexistence of MPs and biochar reduced soil Fluorescein diacetate hydrolase enzyme activity by 46.2% and urease activity by 94.0%. FW addition doubled acid phosphatase activity, whereas FW and its coexistence with MPs decreased alpha diversity. The relative abundance of Actinobacteria decreased with MP application, whereas that of Acidobacteria and Actinobacteria decreased with FW treatment. Gemmatimonadetes and Nitrospirae decreased in soil treated with FW and biochar. The highest relative abundances of Firmicutes and Proteobacteria were observed in the FW-added soils, and Planctomycetes were the highest in the biochar-added soils. FW application negatively affected lettuce growth. Overall, the coexistence of MPs with FW or biochar had limited effects on soil properties and lettuce growth, with FW and biochar serving as the primary factors in modifying soil–plant systems. Future studies should investigate the effects of different MPs and their interactions with organic soil amendments on soil properties and crop growth under different management practices.

中文翻译：

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食物垃圾及其生物炭对微塑料污染土壤中土壤性质和生菜生长的影响对比

将食物垃圾 (FW) 和生物炭等有机改良剂掺入土壤中是一种既定的农艺做法，以提高土壤肥力和改善整体土壤健康而闻名。然而，FW 和生物炭对微塑料 (MP) 污染的土壤-植物系统中土壤性质的单独和综合影响仍知之甚少。为了弥补这一知识差距，我们进行了一项田间实验，研究聚苯乙烯 MP、FW 和 FW 衍生生物炭对土壤特性和生菜生长的单独和组合影响。土壤化学性质不受添加 MP 的影响。然而，FW和生物炭的施用增加了土壤pH值，在生物炭和MPs的联合处理中观察到最高pH值（8.2）。尽管存在 MPs，施用 FW 仍导致土壤电导率（EC；2.04 dS m−1）和有效氮（NO3−–N：325.5 mg kg−1，NH4+–N：105.2 mg kg−1）显着增加。 、有效磷（88.4 mg kg−1）和总可交换阳离子（18.6 cmol(+) kg−1）。然而，生菜种植后这些值有所下降。在生菜种植的土壤中，MPs与生物炭共存使土壤荧光素二乙酸水解酶活性降低46.2%，脲酶活性降低94.0%。FW 的添加使酸性磷酸酶活性加倍，而 FW 及其与 MP 的共存降低了 α 多样性。放线菌的相对丰度随着MP的应用而降低，而酸杆菌和放线菌的相对丰度随着FW处理而降低。在用 FW 和生物炭处理的土壤中，Gemmatimonadetes 和 Nitrospirae 减少。在添加 FW 的土壤中观察到厚壁菌门和变形菌门的相对丰度最高，而浮霉菌在添加生物炭的土壤中相对丰度最高。施用固件对生菜生长产生负面影响。总体而言，MPs与FW或生物炭共存对土壤性质和生菜生长的影响有限，FW和生物炭是改变土壤-植物系统的主要因素。未来的研究应调查不同管理措施下不同 MP 的影响及其与有机土壤改良剂的相互作用对土壤特性和作物生长的影响。