Soil texture controls bioplastic-induced greenhouse gas emissions and carbon-nitrogen cycling in agricultural soils.

Bioplastics (BPs) are increasingly used in agriculture, yet their behavior in soil and effects on carbon (C) and nitrogen (N) cycling depend strongly on soil conditions. This study evaluated the effects of three BPs (1% w/w; 400-700 μm) polyhydroxyalkanoates (PHA), polybutylene succinate (PBS), and polylactic acid (PLA) on soil C and N cycling, microbial activity, and greenhouse gas emissions in clayey and sandy agricultural soils during a 120-day incubation with four wetting-drying cycles (70-30% water-filled pore space). PHA produced the largest changes in soil biochemical processes including higher CO2 emissions, microbial biomass, enzyme activities, and DOC, together with lower NO3- concentrations. Cumulative CO2 emissions increased by up to 464% relative to the control in clayey soil and 107% in sandy soil, while N2O emissions increased by up to 4.2-fold in sandy soil, and NO3- concentrations decreased by up to 59% under PHA treatment. Soil microbial biomass and C- and N-acquiring enzyme activities increased by up to 2-3 fold in clayey soil and 1-2 folds in sandy soil. Dissolved organic carbon also increased in PHA treatment, reaching 748 mg kg-1 in sandy soil compared to 490 mg kg-1 in the control treatment. PLA and PBS caused smaller and delayed changes in C and N pools, with PBS supporting more persistent microbial enrichment than PLA. ATR-FTIR showed polymer- and soil-dependent spectral changes after incubation. However, these spectral changes did not consistently correspond with soil biochemical responses. Soil type influenced the changes in C and N cycling following BPs addition. Sandy soil generally showed higher CO2 and N2O emissions, although the increase in CO2 under PHA relative to the control was greater in clayey soil. These findings show that soil texture strongly influenced bioplastic-induced changes in microbial activity, C and N cycling, and greenhouse gas emissions under repeated wetting-drying conditions. This highlights the importance of soil-specific risk assessments of biodegradable plastics in agricultural soil.