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Warming altered the variational effects of microplastics and leachate from biodegradable mulch films on organic carbon transformation in riparian zones
Summary
A laboratory study explored how biodegradable agricultural mulch films contribute to microplastic pollution and chemical leachate in riverbank sediments, and how rising temperatures alter the effects. Microplastics from the films tended to increase the proportion of less stable, particulate organic carbon in sediments, while leachate from the films promoted the formation of more stable mineral-bound carbon — and warming temperatures reduced the differences between these effects. As biodegradable plastics become more widely used in farming, understanding their full environmental footprint, including effects on soil carbon storage, is increasingly important.
Biodegradable mulch films are extensively utilized in agricultural production, degrade into microplastics (MPs) and release leachate that accumulate in the riparian zone through surface runoff. However, the potential impact of MPs and leachate on sediment organic carbon (SOC) transformation is poorly understood, especially in global warming. This work was performed to analyze the influence of typical films MPs and leachate on the SOC transformation, microbial community structure and function under warming. Results showed that increase in CO emissions of leachate group was greater than MPs group at 15 °C, while reversed at 35 °C. Meanwhile, MPs group increased the sediment carbon stability index (POC/MAOC, CSI) by enhancing the particulate organic carbon (POC) proportion at different temperatures. However, the decrease in CSI of leachate group was observed at 15 and 25 °C, because leachates promoted mineral-associated organic carbon (MAOC) formation. CSI in experimental groups (0.183 ± 0.064-0.254 ± 0.054) was higher than control group (0.179 ± 0.015) due to high microbial diversity and carbon decomposition functions at 35 °C, while the CSI is lower and the sediment carbon stability is stronger, indicating temperature rise narrowed the gap in the impact of different groups on the SOC transformation. These findings help us further understand the differential effects of MPs and leachate from biodegradable films on SOC transformation in freshwater ecosystems under warming.