Effect of plastic mulching on soil organic carbon chemical stability: Insights from soil organic carbon chemical fractions and structure

Plastic mulching (PM) is commonly applied in dryland agriculture to improve crop production on China’s Loess Plateau. With the increasing emphasis on carbon neutrality in agriculture, understanding the PM effect on soil organic carbon (SOC) has become critically important. Most existing studies have focused on the change in SOC content after applying PM, whereas the change in SOC chemical stability remains unclear. Thus, this study conducted a 3-year winter wheat–summer maize rotation experiment to assess the PM effects on crop production, SOC content, carbon-degrading enzyme activities, SOC chemical fractions and structure, and SOC chemical stability. The results indicated that PM increased annual aboveground biomass and grain yield by 8307 and 4189 kg ha⁻¹, respectively, but had no effect on harvest index. Due to increased soil carbon inputs, SOC content under PM was 0.61 g kg⁻¹ greater than that under no mulching (NM). PM positively affected the activities of hydrolytic enzymes (β-glucosidase: +14.4 %; cellobiohydrolase: +25.7 %; β-1,4-xylosidase: +25.9 %) but did not change the activities of oxidative enzymes (polyphenol oxidase and peroxidase). The PM-induced changes in soil carbon inputs and carbon-degrading enzyme activities largely contributed to the changes in SOC chemical fractions and structure. For SOC chemical fractions, the contents of labile carbon pools I and II remained unchanged following PM application, whereas the content of recalcitrant carbon pool increased by 0.66 g kg⁻¹. For SOC chemical structure, NM and PM yielded comparable relative abundance of the alkyl, O-alkyl, aromatic, and carbonyl carbon functional groups. Five SOC chemical stability indices, which were calculated based on SOC chemical fractions and structure, did not differ between PM and NM. Thus, PM did not alter SOC chemical stability. These findings deepen our understanding of SOC sequestration under increased crop production in PM-based dryland agriculture on China’s Loess Plateau.