In November 2025, Professor Wu Wei's team from the Nanfan College of Hainan University published a research paper entitled "Biodegradable plastic exposure enhances microbial functional diversity while reducing taxonomic diversity across multi-kingdom soil microbiota in cherry tomato fields" in Communications Biology.
Research Background: Is biodegradable plastic really "friendly"?
Traditional polyethylene (PE) mulch film is widely used in farmland. Incomplete removal of residual film causes serious soil plastic pollution. Therefore, people have turned to PBAT (a petroleum-based biodegradable polyester), which can gradually hydrolyze in the soil. However, the problem is that if PBAT does not degrade completely, it actually produces more microplastic fragments than PE. Its impact on the "functional level" of soil microorganisms has been almost never systematically studied in the past.
How the experiment was conducted: The research team cultivated cherry tomatoes for two years at the Ledong experimental station in Hainan. They mixed PE and PBAT film fragments into the soil at different concentrations (0, 800, 4000 kg/ha) and sampled four microhabitats: large soil masses, rhizosphere, root zone, and "plastic spheres" tightly adhered to the plastic surface. They used amplicon sequencing to analyze the species composition of the three kingdoms of bacteria, fungi, and protists, and performed metagenomic sequencing on representative samples to examine functional genes.
Key findings: Decoupling of species and function
The results were unexpected-under PBAT exposure, the species diversity of the three kingdoms of microorganisms decreased significantly (in the plastic spheres, the Chao1 index of bacteria, fungi, and protists decreased by 65%, 58%, and 45%, respectively, compared to PE treatment), but the diversity of functional genes increased.
Specifically:
• Enrichment of plastic degradation genes: The abundance of genes such as tfdB, pcaG, and Ad increased significantly. These genes encode enzymes that can cleave plastic derivatives such as chlorinated aromatics, styrene, and polycyclic aromatic hydrocarbons.
• Genes involved in the carbon, nitrogen, phosphorus, and sulfur cycles are comprehensively upregulated: such as nifH/K (involved in nitrogen fixation), norC (involved in denitrification), and napA/B (involved in the DNRA pathway).
• The average microbial genome size increased by 18.9%, meaning the surviving species are "better equipped."
• Soil enzyme activity is enhanced: β-glucosidase and cathepsins, among others, increased by 9% to 46%.
Why is this happening?
The paper explains it as "environmental filtering":
• PBAT is hydrophilic; after ester bond hydrolysis, it produces water-soluble low-molecular-weight oligomers, becoming a "premium" for certain microorganisms.
• Species that can obtain this food (such as the Bacillus subtilis and Xanthomonadaceae families) proliferate rapidly, while those that cannot are eliminated.
• The result is a decrease in the total number of species, but those that remain are "functionally powerful," carrying abundant degradation genes and metabolic pathways.
This leads to a "decoupling" of taxonomic diversity and functional diversity-previously, we believed that "the more species, the more comprehensive the functions," but under PBAT pressure, a few specific species can support or even surpass the original functional network.
The accompanying concerns are also evident: Under PBAT treatment, the complexity and stability of cross-kingdom and intra-kingdom co-occurrence networks of microorganisms decrease significantly-fewer nodes, sparser connections, and weaker resistance to disturbance. In other words, the ecosystem becomes "fragile but efficient."
What this study tells us:
💡Evaluating the environmental impact of biodegradable plastics cannot solely rely on species richness. Even if the "species" of microorganisms in the soil decreases, their functional potential (especially pollutant degradation and nutrient cycling) may actually be stimulated.
This is a double-edged sword for sustainable agricultural development: on the one hand, PBAT does activate the soil's "detoxification and cycling" functions; on the other hand, the fragility of microbial networks may weaken the resilience of ecosystems on a long-term scale. Researchers also acknowledge that the actual degradation rate of PBAT in the field is approximately 20%–60%, and is highly dependent on environmental conditions; long-term, multi-regional monitoring remains crucial for the next step.
In short, PBAT mulch film reduces the number of soil microorganisms but increases their capabilities. This "less is more" reconstruction is both a miracle of adaptive evolution and a warning sign of ecological risks.
