As a crucial agricultural yield-increasing technique in arid and semi-arid regions, plastic film mulching (PFM) has significantly enhanced crop yield and quality by increasing soil temperature, reducing water evaporation, and optimizing nutrient cycling. However, with the increasingly prominent issue of farmland microplastic pollution caused by residual plastic films, this "white revolution" is now facing severe challenges to sustainable development.
Professor Xuejun Liu and Associate Professor Kai Wang from the College of Resources and Environmental Sciences, China Agricultural University, and their colleagues have systematically revealed the complex impact mechanisms of PFM and microplastics on soil nitrogen cycling processes through a review study, providing important scientific references for the green development of agriculture. The related paper was published in Frontiers of Agricultural Science and Engineering (DOI: 10.15302/J-FASE-2025642).
Nitrogen, as the mineral nutrient most demanded by crops, its cycling process in soil is directly related to the safe production of food and the stability of the ecological environment. The study points out that although PFM promotes crop nitrogen uptake and microbial activity by improving soil hydrothermal conditions, it also increases the emission risk of greenhouse gases such as nitrous oxide (N₂O). More notably, microplastics (with a diameter < 5 mm) formed by the decomposition of residual plastic films are profoundly affecting the key links of nitrogen transformation by altering soil physicochemical properties and microbial community structure.
The impact of PFM on soil nitrogen cycling is two-sided. On one hand, traditional polyethylene (PE) plastic films can increase the total nitrogen content in the 0–20 cm soil layer, making the microbial biomass nitrogen content 23.6% higher than that in bare soil; on the other hand, due to the physical barrier effect of plastic films, the total N₂O emissions under PFM are reduced by 12%–41%. Although biodegradable plastic films show advantages in emission reduction in the short term, the impact of their degradation products on soil dissolved organic nitrogen is significantly stronger than that of ordinary plastic films, which may be related to the additional carbon sources provided by the decomposition of polylactic acid (PLA).
The cumulative effect of microplastics is more complex. When the concentration of polypropylene microplastics in soil reaches 1%, peanut root cells are damaged, and nitrogen uptake is inhibited; while 1% PE microplastics can increase N₂O emissions from paddy soils by 3.7 times. In addition, the impact of microplastics on nitrogen cycling functional genes is selective: they significantly increase the abundance of nitrogen-fixing genes (nifH) and urea hydrolysis genes (ureC), while inhibiting the expression of nitrification genes (amoA). This differential regulation of gene expression leads to an imbalance in soil nitrogen during the "fixation-mineralization-nitrification" transformation process.
There are significant differences in the impacts of different types of microplastics. For microplastics from biodegradable plastic films containing 85% polybutylene adipate terephthalate (PBAT), their impact on soil available nitrogen is stronger than that of traditional low-density polyethylene (LDPE) plastic films. This may be because biodegradable plastics decompose faster in soil, providing more carbon sources for nitrogen-cycling microorganisms and accelerating the decomposition and transformation of organic nitrogen.
This study systematically sorts out the impact pathways of PFM and microplastics on various links of soil nitrogen cycling in existing studies, and emphasizes that these impacts are jointly regulated by plastic type, environmental conditions, and crop growth stages. The study suggests that future research should focus on conducting long-term fixed-position observations and combining advanced statistical models to quantify the dynamic impacts of microplastics in complex natural environments. The control of agricultural plastic pollution needs to balance food security and ecological protection, and the relevant results provide a theoretical basis for the scientific formulation of plastic film management strategies.
DOI: 10.15302/J-FASE-2025642