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Microplastic induces microbial nitrogen limitation further alters microbial nitrogentransformation: Insights from metagenomic analysis
Summary
Researchers studied how both conventional and biodegradable microplastics affect nitrogen cycling in soil over 120 days. They found that biodegradable microplastics significantly disrupted microbial nitrogen processes by acting as a carbon source that shifted bacterial communities toward nitrogen-fixing species. The findings suggest that even biodegradable plastics in soil can alter nutrient availability in ways that may affect soil fertility and plant growth.
Microplastic has a significant impact on soil microbial communities, which play crucial roles in soil nitrogen (N) cycles. However, there is a limited understanding of their influences on genes associated with the entire N cycling pathways. Through a 120-day soil incubation using conventional (PE and PET) and biodegradable microplastics (PLA and PBAT), coupled with 16S rRNA and metagenomic sequencing, we investigated the responses of N-cycling genes to microplastics in two contrasting soils (i.e. black soil and loess soil). We found that biodegradable microplastics strongly altered microbial N functional profiles, and enhanced the abundance of numerous key genes involved in N fixation, organic N mineralization, N reduction, and denitrification. Furthermore, biodegradable microplastics significantly decreased net N mineralization (Nm) compared to control and conventional microplastic treatments, suggesting microbial N immobilization outweighed N mineralization. Analysis of the function-taxon bipartite network showed that the Nm was well predicted for the abundances and diversity of bacteria within specific modules, with Nm decreasing, the abundances of specific taxa in a given network modules increasing. These results indicated that biodegradable microplastics act as a carbon source to select specific taxa involved in enhancing N bioavailability (e.g., N fixation and organic N mineralization) to meet microbial N demand, which in turn filtered the bacterial community (decreased diversity but increased abundances) and gradually formed specific function-taxon modules. Comparing the two soils, microbes in the less fertile alkaline loess soil were more sensitive to biodegradable microplastics than those in the nutrient-rich acid black soil. Our study indicated that increasing usage of biodegradable plastics in the future may lead to accelerated soil microbial N limitation and transformation.
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