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Depth-dependent response of soil microbial community and greenhouse gas efflux to polylactic acid microplastics and tidal cycles in a mangrove ecosystem
Summary
Researchers found that biodegradable plastic (PLA) microplastics in mangrove soil increased the release of greenhouse gases, especially carbon dioxide and methane, from deeper soil layers. The microplastics altered soil bacterial communities in ways that boosted methane-producing organisms. This finding is important because biodegradable plastics are often marketed as environmentally friendly, but they may still harm ecosystems by accelerating carbon release from soils.
The impacts of microplastics (MPs) on greenhouse gas emissions from mangrove soil remain poorly understood. Previous studies mostly focused on the topsoil in stable inundation state, ignoring the effects of natural tidal cycle and deep soil under different soil oxygen conditions. In this study, we analyzed soil microbial communities and greenhouse gas emissions from mangrove soils across various depths and tidal conditions (by adding seawater to create different inundation durations) in response to polylactic acid (PLA) MP exposure. Results indicated that PLA MPs addition enhances CO and CH release from the continuously anaerobic subsoil (100-120 cm). With increasing submersion duration, PLA MPs facilitate the emission of CH from the topsoil (0-5 cm). An elevated C:N ratio may promote microbial nitrogen mining and organic carbon mineralization, indicating the threat of PLA MPs to soil carbon and nitrogen pools. PLA MPs addition significantly altered the bacterial community structure and reduced bacterial diversity in the subsoil. Increases in the abundance and functioning of communities associated with methanogenesis and sulfate reduction contributed to the release of CO and CH. The duration of inundation had no significant impact on the microbial community structure in the topsoil. These findings demonstrate the accelerating effect of PLA MPs on organic carbon mineralization and carbon release, which was critically regulated by the soil depth and tidal inundation.