Abstract：
The current carbon dioxide (CO2) evolution-based standard method for determining biodegradable microplastics (MPs) degradation neglects its priming effect on soil organic matter decomposition, which misestimates their biodegradability. Here, a 13C natural abundance method was used to estimate the mineralization of poly(lactic acid) (PLA) MP in various agricultural soils, and to trace its utilization in different microbial groups. In alkaline soils, the PLA-derived CO2 emissions increased with increasing soil carbon/nitrogen (C/N) ratios, and the mineralization of PLA MP concentrations ranged from 3-33 %, whereas the CO2 evolution method probably over- or under-estimated the mineralization of PLA in alkaline soils with different soil C/N ratios. Low PLA mineralization (1-5 %) were found in the acidic soil, and the standard method largely overestimated the mineralization of PLA MP by 1.3- to 3.3-fold. Moreover, the hydrolysate of PLA MP was preferentially assimilated by Gram-negative bacteria, but Gram-positive bacterial decomposition mainly contributed to the release of PLA-derived CO2 at low MP concentrations (≤ 1 %). Overall, the 13C natural abundance method appears to be suitable for tracking the mineralization and microbial utilization of biodegradable PLA in soils, and the PLA-derived C is mainly assimilated and decomposed by bacterial groups.
摘要：
当前基于二氧化碳（CO2）释放的用于确定可生物降解的微塑料（MPs）降解的标准方法忽略了其对土壤有机质分解的启动作用，错误地估计了它们的生物降解性。这里,13C自然丰度方法用于估算各种农业土壤中聚（乳酸）（PLA）MP的矿化，并追踪其在不同微生物群中的利用。在碱性土壤中，PLA衍生的CO2排放量随着土壤碳/氮(C/N)比的增加而增加，PLAMP浓度的矿化范围为3-33%，而CO2释放方法可能高估或低估了不同土壤C/N比的碱性土壤中PLA的矿化。在酸性土壤中发现低PLA矿化（1-5％），标准方法大大高估了PLAMP的矿化1.3至3.3倍。此外，PLAMP的水解产物优先被革兰氏阴性菌同化，但是革兰氏阳性菌的分解主要是在低MP浓度（≤1％）下释放PLA衍生的CO2。总的来说,13C自然丰度方法似乎适用于跟踪土壤中可生物降解PLA的矿化和微生物利用，PLA来源的C主要被细菌群吸收和分解。
