The effect of microplastic pollution on rice growth, paddy soil properties, and greenhouse gas emissions: A global meta-analysis

Microplastic (MP) pollution has emerged as a global environmental concern, posing threats to various ecosystems, including agricultural lands. Paddy fields, critical for global food security, are particularly vulnerable. However, the specific effects of MP contamination on rice production, paddy soil properties, and greenhouse gas (GHG) emissions in these systems remain unclear. In this study, we conducted a comprehensive meta-analysis by synthesizing experimental observations from 40 published articles worldwide to determine the impact of MPs on rice, paddy soil properties, and GHG emissions, and whether these impacts depend on MP characteristics and experimental variables. We found that MPs could reduce rice stem and root biomass by inducing reactive oxygen species and inhibiting photosynthesis. MPs decreased soil total nitrogen (TN), total phosphorus (TP), nitrate (NO₃⁻-N), available phosphorus (AP), ammonium (NH₄⁺-N), and organic carbon (TOC) by enriching specific microbial populations or altering soil nutrient cycling. Additionally, MPs stimulate nitrogen mineralization, nitrification, and nitrite reduction in paddy soils, thereby increasing nitrous oxide (N₂O) emissions. Moreover, MP significantly increased the ACE index of paddy soil bacteria, suggesting a mechanism by which they affect soil microbial communities by reducing evenness and amplifying dominant species. Notably, the negative response of TOC to conventional MPs was stronger than that to biodegradable MPs. Large-sized MPs (>100 μm) had a positive effect on N₂O emissions but had adverse effects on TOC and soil organic matter (SOM) content. Moreover, AP, available potassium (AK), TOC, dissolved organic carbon (DOC), and CH₄ emissions were associated with the duration of MP exposure. The total biomass of rice, CH₄ and N₂O emissions, TOC, Shannon index, and Simpson index were related to MP concentration. In conclusion, our results indicate that MPs may threaten paddy soil fertility and rice production and exert environmental pressure. This study provides essential references for green and efficient rice production under MP pollution.