[Ecoenzymatic Stoichiometry During Straw Carbon Mineralization and Soil Organic Carbon Priming Effects under...

Microplastics （MPs）， emerging contaminants in agroecosystems， have garnered increasing attention due to their environmental effects and potential impacts on soil ecological processes. To elucidate the dynamics of straw carbon （C） mineralization and its priming effect （PE） on soil organic carbon （SOC） under polyethylene MPs addition， a ¹³C-stable isotope labeling approach was employed to partition CO₂ emissions derived from straw and soil original organic C （OC）. Additionally， the activities of key enzymes involved in C and N cycling were analyzed to reveal the effects of MPs on the enzymatic mechanisms during straw C and SOC decomposition. The results showed that MPs had no significant effect on the total mineralization of straw C or soil original OC. However， low-dose MPs （0.1 mg·g^-1） amplified the negative PE of straw-induced SOC mineralization by 231% （P<0.05）. Compared to that under straw-amended treatments， high-dose MPs （10 mg·g^-1） significantly reduced cellobiohydrolase （CBH） activity by 61.9% and 53.4% on days 30 and 65 （P<0.05）， respectively， while enhancing leucine aminopeptidase （LAP） activity by 28.9% on day 30 （P<0.05） and peroxidase （PER） activity by 92.6% and 205.5% on days 3 and 15 （P<0.05）. On days 3 and 15 during incubation， low-dose MPs decreased the ratios of C-hydrolase to PER by 20.3% and 24.0%， respectively， and decreased N-hydrolase to PER by 21.1% and 23.8% （P<0.05）. High-dose MPs decreased the ratios of C-hydrolase to PER by 20.1% and 35.9%， respectively， and decreased N-hydrolase to PER by 19.3% and 32.4% （P<0.05）. These findings demonstrate that polyethylene MPs at the dosage of 0.1 and 10 mg·g^-1 did not directly alter straw C or SOC mineralization but regulated the negative PE of straw on SOC mineralization by reshaping enzymatic activities and stoichiometry in paddy soils.