Nitrogen and Phosphorus Availability Effect on Activity of Cellulolytic Microorganisms in Meadows

Does poly-3-hydroxybutyrate biodegradation affect the quality of soil organic matter?

The search for eco-friendly substitutes for traditional plastics has led to the production of biodegradable bioplastics. However, concerns have been raised about the impact of bioplastic biodegradation on soil health. Despite these concerns, the potential negative consequences of bioplastics during various stages of biodegradation remain underexplored. Therefore, this study aims to investigate the impact of micro-bioplastics made of poly-3-hydroxybutyrate (P3HB) on the properties of three different soils. In our ten-month experiment, we investigated the impact of poly-3-hydroxybutyrate (P3HB) on Chernozem, Cambisol, and Phaeozem soils. Our study focused on changes in soil organic matter (SOM), microbial activity, and the level of soil carbon and nitrogen. The observed changes indicated an excessive level of biodegradation of SOM after the soils were enriched with micro-particles of P3HB, with concentrations ranging from 0.1% to 3%. The thermogravimetric analysis confirmed the presence of residual P3HB (particularly in the 3% treatment) and underscored the heightened biodegradation of SOM, especially in the more stable SOM fractions. This was notably evident in Phaeozem soils, where even the stable SOM pool was affected. Elemental analysis revealed changes in soil organic carbon content following P3HB degradation, although nitrogen levels remained constant. Enzymatic activity was found to vary with soil type and responded differently across P3HB concentration levels. Our findings confirmed that P3HB acts as a bioavailable carbon source. Its biodegradation stimulates the production of enzymes, which in turn affects various soil elements, indicating complex interactions within the soil ecosystem.

Fertilization accelerates the decomposition of microplastics in mollisols

Agricultural films composed of low-density polyethylene (LDPE) have been widely used in farmland, and LDPE microplastics (LDPE-MPs) produced from LDPE degradation can pollute soils and can exert negative effects on biota. Both nitrogen (N) and phosphorus (P) can alter the activity of soil microorganisms and may alter the LDPE-MP degradation process in soils. In this study, LDPE-MP surface morphology, particle size, abundance and mass in a mollisol were evaluated after the application of a gradient of N and P fertilizer in a laboratory incubation experiment. The results showed the following: (1) LDPE-MP particles became fragmented into smaller debris with a coarse surface after 40 days of incubation, and the effect was more obvious with increased P or N application; (2) high N and P fertilization significantly reduced the abundance of LDPE-MP particles >100 μm by 38.5-50.0% and increased the abundance of LDPE-MP particles <20 μm by 43.2-59.5% after 40 days of incubation; (3) high N and P fertilization significantly increased the mass of LDPE-MP particles <75 μm by 25.5-60.1% and decreased the mass of LDPE-MP particles >150 μm by 32.4-37.5%; (4) the mass of LDPE-MPs decreased with increasing incubation time after N and P fertilization, which could be simulated by exponential models (p < 0.05), LDPE degradation was rapid in the first 20 days after N or P fertilization, and both N and P caused a "priming effect" of LDPE degradation; and (5) N and P fertilization increased both the biodiversity and abundance of several predominant genera of soil microorganisms that degrade LDPE. Therefore, N and P fertilization can accelerate LDPE-MP degradation, and the relatively large amounts of fine debris from degraded LDPE-MPs can be problematic for the environment and soil biota. LDPE-MP pollution should be strictly controlled in mollisols, and the degradation mechanisms of LDPE-MPs warrant further study.