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Biodegradable Microplastic-Driven Change in Soil pH Affects Soybean Rhizosphere Microbial N Transformation Processes
Summary
Researchers found that biodegradable microplastics made from polybutylene succinate (PBS) caused more harm to soil health than conventional polyethylene microplastics in soybean-growing systems. The biodegradable plastic acidified the soil, disrupted microbial communities responsible for nitrogen cycling, and impaired plant nutrient uptake. This challenges the assumption that biodegradable plastics are always safer for agricultural environments.
The potential impacts of biodegradable and nonbiodegradable microplastics (MPs) on rhizosphere microbial nitrogen (N) transformation processes remain ambiguous. Here, we systematically investigated how biodegradable (polybutylene succinate, PBS) MPs and nonbiodegradable (polyethylene, PE) MPs affect microbial N processes by determining rhizosphere soil indicators of typical Glycine max (soybean)-soil (i.e., red and brown soils) systems. Our results show that MPs altered soil pH and dissolved organic carbon in MP/soil type-dependent manners. Notably, soybean growth displayed greater sensitivity to 1% (w/w) PBS MP exposure in red soil than that in brown soil since 1% PBS acidified the red soil and impeded nutrient uptake by plants. In the rhizosphere, 1% PBS negatively impacted microbial community composition and diversity, weakened microbial N processes (mainly denitrification and ammonification), and disrupted rhizosphere metabolism. Overall, it is suggested that biodegradable MPs, compared to nonbiodegradable MPs, can more significantly influence the ecological function of the plant-soil system.