Microplastics (MPs) in agricultural plastic film mulching system changes microbial functions and nutrient dynamics in soils. However, how biodegradable MPs impact the soil gross nitrogen (N) transformations and crop N uptake remain significantly unknown. In this study, we conducted a paired labeling N tracer experiment and microbial N-cycling gene analysis to investigate the dynamics and mechanisms of soil gross N transformation processes in soils amended with conventional (polyethylene, PE) and biodegradable (polybutylene adipate co-terephthalate, PBAT) MPs at concentrations of 0 %, 0.5 %, and 2 % (w/w). The biodegradable MPs-amended soils showed higher gross N mineralization rates (0.5–16 times) and plant N uptake rates (16–32 %) than soils without MPs (CK) and with conventional MPs. The MPs (both PE and PBAT) with high concentration (2 %) increased gross N mineralization rates compared to low concentration (0.5 %). Compare to CK, MPs decreased the soil gross nitrification rates, except for PBAT with 2 % concentration; while PE with 0.5 % concentration and PBAT with 2 % concentration increased but PBAT with 0.5 % concentration decreased the gross N immobilization rates significantly. The results indicated that there were both a concentration effect and a material effect of MPs on soil gross N transformations. Biodegradable MPs increased N-cycling gene abundance by 60–103 %; while there was no difference in the abundance of total N-cycling genes between soils without MPs and with conventional MPs. In summary, biodegradable MPs increased N cycling gene abundance by providing enriched nutrient substrates and enhancing microbial biomass, thereby promoting gross N transformation processes and maize N uptake in short-term. These findings provide insights into the potential consequences associated with the exposure of biodegradable MPs, particularly their impact on soil N cycling processes.

中文翻译：

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通过可生物降解的微塑料调节微生物氮循环基因来增强土壤总氮转化


农用地膜覆盖系统中的微塑料（MP）改变了土壤中的微生物功能和养分动态。然而，可生物降解的 MP 如何影响土壤总氮 (N) 转化和作物氮吸收仍然非常未知。在本研究中，我们进行了配对标记氮示踪实验和微生物氮循环基因分析，以研究传统土壤（聚乙烯，PE）和可生物降解土壤（聚己二酸-对苯二甲酸丁二酯， PBAT) MP 浓度为 0%、0.5% 和 2% (w/w)。与不含 MPs (CK) 和含有传统 MPs 的土壤相比，可生物降解 MPs 改良的土壤显示出更高的总氮矿化率（0.5-16 倍）和植物氮吸收率（16-32%）。与低浓度（0.5%）相比，高浓度（2%）的 MP（PE 和 PBAT）增加了总氮矿化率。与CK相比，除2%浓度的PBAT外，MPs均降低了土壤总硝化率；而0.5%浓度的PE和2%浓度的PBAT增加了总氮固定率，但0.5%浓度的PBAT显着降低了总氮固定率。结果表明，MPs对土壤全氮转化同时存在浓度效应和物质效应。可生物降解的 MP 将氮循环基因丰度增加 60-103%；而在没有 MP 的土壤和有传统 MP 的土壤之间，总氮循环基因的丰度没有差异。总之，可生物降解的 MP 通过提供丰富的营养底物和增强微生物生物量来增加氮循环基因丰度，从而促进总氮转化过程和玉米短期氮吸收。 这些发现为了解与可生物降解的 MP 的暴露相关的潜在后果提供了见解，特别是它们对土壤氮循环过程的影响。