The presence of biodegradable microplastics (BMPs) alongside toxic metals in soil significantly threatens plant health. Current research mainly focuses on the effects of original BMPs. In contrast, the specific impacts of ultraviolet (UV)-aged BMPs and their interaction with Cadmium (Cd) on seed germination and growth are unclear. Therefore, this study incubated aged polylactic acid (PLA) MPs through a UV irradiation aging process and used an indoor hydroponic experiment to systematically investigate the single and combined effects of Cd and BMPs (virgin and aged) on pakchoi (Brassica chinensis L.) germination, photosynthesis, antioxidant systems, and Cd accumulation. The results showed that after 21 days of UV irradiation (UPLA MPs), PLA MPs formed a fractured surface, demonstrating more detrimental effects on pakchoi than virgin ones. UPLA MPs and Cd alone inhibited pakchoi germination, growth, and photosynthesis, while PLA MPs alone promoted these processes. Combined treatment with Cd and UPLA MPs significantly increased oxidative damage and reduced pakchoi root length, chlorophyll, Mg, Mn, and Zn content. Under the combination of Cd and BMPs, PLA MPs could effectively alleviate the toxic effect of Cd on pakchoi. The results unraveled here emphasized that UPLA MPs, especially aged BMPs, could trigger adverse effects on agro-systems with heavy metals. Therefore, the results of this study can provide a new perspective and reference for the ecological risk evaluation of Cd and BMPs pollution in agricultural soils.

Modern agriculture is troubled by white pollution caused by nondegradable polyethylene (PE) mulch film and high transportation costs caused by the large amount of water in liquid mulch film. Aiming at these problems, this study developed a new degradable and water-free powder mulch film (SUPM) with straw powders, urea, and polyvinyl alcohol (PVA) as raw materials. The wind erosion resistance and film-forming properties of SUP powders as SUPM's precursor were investigated as well as the influence of PVA and urea content on the mechanical properties and water resistance of SUPM film. The results showed that PVA in SUPM film was in a gradient distribution conducive to the germination of crop seedlings. Here, PVA colloids were more distributed at the interface between film and air than at the interface between film and soil. The optimized SUPM film exhibited a biodegradation rate of 90.5 % over 100 d. After SUPM film degradation, soil carbon and nitrogen contents were 33.5 and 58.8 % higher, respectively, than in bare soil. In two consecutive planting experiments, pakchoi yields were higher and more stable in the soil with SUPM than in bare soil and soil with PE. Compared to other reported biodegradable mulch films, SUPM demonstrated advantages in ease of use, enhancement of soil carbon and nitrogen content, and stable crop yields. This study provided a new approach for the large-scale utilization of straw waste, mitigating environmental issues caused by traditional PE mulch, and promoting the development of environment-friendly modern agriculture.

Soil salinization is a major factor threatening global food security. Soil improvement strategies are therefore of great importance in mitigating the adverse effect of salt stress. Our study aimed to evaluate the effect of biochar (BC) and nitric acid-modified biochar (HBC) (1%, 2%, and 3%; m/m) on the properties of salinized soils and the morphological and physiological characteristics of pakchoi. Compared with BC, HBC exhibited a lower pH and released more alkaline elements, reflected in reduced contents of K+, Ca2+, and Mg2+, while its hydrophilicity and polarity increased. Additionally, the microporous structure of HBC was altered, showing a rougher surface, larger pore size, pore volume, specific surface area, and carboxyl and aliphatic carbon content, along with lower aromatic carbon content and crystallinity. Moreover, HBC application abated the pH of saline soil. Both BC and HBC treatments decreased the sodium absorption rate (SAR) of saline soil as their concentration increased. Conversely, both types of biochar enhanced the cation exchange capacity (CEC), organic matter, alkali-hydrolyzable nitrogen, and available phosphorus and potassium content in saline soils, with HBC demonstrating a more potent improvement effect. Furthermore, biochar application promoted the growth-related parameters in pakchoi, and reduced proline and Na+ content, whilst increasing leaf K+ content under salt stress. Biochar also enhanced the activity of key antioxidant enzymes (superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT)) in leaves, and reduced hydrogen peroxide (H2O2) and malondialdehyde (MDA) content. Collectively, modified biochar can enhance soil quality and promote plant growth in saline soils.