Microplastics Influence Dissolved Organic Matter Transformation Mediated by Microbiomes in Soil Aggregates

Area of Science:

• Environmental Science
• Soil Science
• Ecology

Background:

• Soil aggregate stability is crucial for soil health, fertility, and crop production.
• Dissolved organic matter (DOM) turnover significantly influences soil aggregate stability and microbial activity.
• Microplastics (MPs) are emerging contaminants affecting soil properties, but their impact on DOM transformation within soil aggregates is not well understood.

Purpose of the Study:

• To investigate the effects of nondegradable and biodegradable microplastics (MPs) on dissolved organic matter (DOM) transformation within agricultural soil aggregates.
• To elucidate the mechanisms by which MPs influence DOM composition, structure, and stability in different aggregate sizes.
• To assess the role of microbial communities in mediating MP-induced changes in DOM and aggregate stability.

Main Methods:

• Incubation assays of agricultural soil aggregates were conducted over 450 days.
• Nondegradable and biodegradable MPs, with varying aging levels, were added to soil aggregates.
• DOM composition, structure, and aggregate stability (geometric mean diameter, mass-weighted diameter) were analyzed.

Main Results:

• Microplastic (MP) addition increased DOM transformation, reducing soil aggregate stability (geometric mean diameter and mass-weighted diameter).
• MPs decreased DOM stability in large aggregates but increased DOM aromaticity and unsaturation in small aggregates.
• Microbial communities consumed DOM in larger aggregates and produced DOM in smaller ones, leading to DOM accumulation in small aggregates and reduced overall stability.

Conclusions:

• Microplastics significantly alter DOM transformation pathways within soil aggregates, negatively impacting soil aggregate stability.
• The observed changes in DOM characteristics and microbial activity provide insights into the mechanisms of MP-soil interactions.
• Understanding these processes is essential for developing strategies for sustainable soil management in the presence of microplastic pollution.