Adverse effects of biodegradable mulch-film microplastics on Daphnia magna: Integrating energy budget, amino-acid profiling, and gene expression

초록

Biodegradable mulch films are increasingly applied in agricultural systems; however, their incomplete degradation generates biodegradable microplastics (BMPs) that may enter freshwater ecosystems. We investigated the 16-day chronic effects of four BMP types—polylactic acid (PLA), poly (butylene adipate-co-terephthalate) (PBAT), pristine mulch film (PMF) consisting of PLA and PBAT, and additive-free mulch film (AMF)—on Daphnia magna. Survival, somatic growth, internal microplastic burden, biochemical energy reserves, total available energy (Ea), expression of energy- and lipid-metabolism-related genes, and targeted amino-acid profiles were jointly assessed. Across all treatments, Ea remained comparable to the unexposed control, indicating that chronic exposure did not induce overall energy depletion. Instead, pronounced material-specific shifts in energy allocation (Ea ratios) were observed. PLA exposure reduced survival and body length and was associated with a protein-biased energy allocation pattern, accompanied by changes in carbohydrate and lipid reserves, suppression of mitochondrial gene expression, and coordinated changes in amino acid composition, suggesting altered energy allocation under persistent stress. PMF exposure caused moderate growth inhibition and lipid loss while promoting a carbohydrate-biased energy allocation strategy, together with transcriptional responses in mitochondrial and lipid-metabolism-related genes, indicating potential additive-associated metabolic responses. However, PBAT and AMF elicited minimal changes in survival, growth, and metabolic endpoints, consistent with weaker energetic disturbance. Targeted amino acid profiling showed only modest variation in individual amino acid concentrations; however, ratio-based analysis revealed coordinated shifts in amino acid composition. These findings indicated that the ecological effects of biodegradable mulch film–derived microplastics are governed by material-specific metabolic reorganization rather than generalized energy depletion, underscoring the value of integrative energy budgets, targeted amino acid profiling, and gene expression analyses for assessing long-term sublethal impacts in freshwater environments. © 2026 Elsevier Ltd. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

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