ABSTRACT

Microplastics cause environmental problems. Biodegradable plastics have become popular because they aim to avoid such problems. However, their decomposition in the soil may have an impact. This study aims to investigate the effects of biodegradable plastics on the physicochemical properties of soil, specifically the production of CO₂ and N₂O in the soil and plant growth. Three kinds of biodegradable plastics in the forms of 1) nonwoven fabric sheets made of poly-lactic acid (PLA) and polybutylene-succinate (referred to hereafter as fabric), 2) laminate sheets made of polybutylene adipate terephthalate (PBAT) and pulp (hereafter laminate), and 3) drinking cups made of PLA (hereafter cup), were cut into small pieces (<5 mm), added to soil, then water-holding capacity was determined and incubated aerobically for 4 weeks at 30°C in the dark. Soil and gas samples were collected weekly to measure soil pH, nitrate-nitrogen content, CO₂, and N₂O productions. These plastics were also tested in a pot experiment with Komatsuna (Brassica napa var. perviridis). We tested for seed germination, plant growth, leaf color, and fresh weight at harvest. Results showed that the water retention capacity was higher in the fabric plastics as compared to the cup plastics and the control. Soil pH with the fabric plastics dropped during the initial 2 weeks of incubation, then recovered to a similar pH to the control (without plastic). Nitrate contents in the soil with laminate plastics were lower than those in the control, while CO₂ production in the soil with the laminate plastics was higher than that in the control and the other plastics during the incubation period, and even higher than the one of added plastic-C. N₂O was produced rapidly within 1 week of incubation in the soil with the laminate plastics, and cumulative N₂O production from incubation was more than that of the control. The seed germination and plant growth tended to be suppressed in the pot experiment with the fabric and laminate plastics. The results indicate that the influence of these biodegradable plastics on soil properties, greenhouse gas production, and plant growth on the kind of plastic and the timing.

摘要

微塑料会导致环境问题。可生物降解塑料之所以流行，是因为它们旨在避免此类问题。然而，它们在土壤中的分解可能会产生影响。本研究旨在研究可生物降解塑料对土壤理化性质的影响，特别是对土壤中 CO ₂和 N ₂ O 的产生和植物生长的影响。三种可生物降解塑料的形式：1）由聚乳酸（PLA）和聚丁二酸丁二醇酯制成的无纺布片材（以下简称织物），2）由聚己二酸对苯二甲酸丁二醇酯（PBAT）和纸浆制成的层压片材（下文称为层压板），以及 3) PLA 制成的饮水杯（下文称为杯子)，切成小块（<5 mm），添加到土壤中，然后测定持水能力，并在 30°C 的黑暗中有氧培养 4 周。每周收集土壤和气体样品以测量土壤 pH 值、硝酸盐-氮含量、CO ₂和 N ₂ O 产量。这些塑料也在小松菜（Brassica napa var. perviridis）的盆栽实验中进行了测试。我们在收获时测试了种子发芽、植物生长、叶色和鲜重。结果表明，与杯子塑料和对照相比，织物塑料的保水能力更高。土壤pH值与织物塑料在最初的 2 周孵化期间下降，然后恢复到与对照（没有塑料）相似的 pH 值。覆膜塑料土壤中硝酸盐含量低于对照，而覆膜塑料土壤中CO ₂产生量在孵化期内高于对照和其他塑料，甚至高于其中一种。添加塑料-C。N ₂ O 在与层压塑料一起在土壤中孵化的1 周内迅速产生，并且孵化的累积N ₂ O 产量超过对照。在盆栽试验中，种子发芽和植物生长往往受到抑制。织物和层压塑料。结果表明，这些可生物降解塑料对土壤性质、温室气体产生和植物生长的影响对塑料的种类和时间都有影响。