不同浓度和表面修饰的聚苯乙烯微塑料对水稻种子萌发、生长和氧化应激的影响

为揭示微塑料对陆生植物的影响，本研究探究了不同表面修饰（原始、羧基化和氨基化）的聚苯乙烯微球（PS、PSC、PSN）暴露下水稻种子萌发、生长和氧化应激状况，暴露浓度分别为0.2、1、5 mg·L^-1和30 mg·L^-1。结果表明，3种微塑料对水稻种子发芽率和幼苗根质量的抑制程度表现为PSN＞PSC＞PS，对水稻根系形态（根长、根表面积和根投影面积）的抑制程度总体表现为两种经表面修饰的微球强于原始微球。PS在较低浓度（0.2、1 mg·L^-1）下通过刺激水稻根部提高抗氧化系统的应激水平，避免了氧化损伤；随着浓度的升高，根部抗氧化防御能力逐渐减弱，在30 mg·L^-1时引发了脂质过氧化。两种经表面修饰的微塑料在较低浓度（0.2、1 mg·L^-1）下即可抑制根部抗氧化系统。PSC仅在最高浓度（30 mg·L^-1）下诱导了根部氧化损伤，而 PSN在 1 mg·L-1时就引发了氧化损伤，且随着PSN浓度的升高，氧化损伤进一步加剧。随着微塑料浓度的升高，水稻根表洗脱物明显增多，可能与根部的抗氧化反应有关。最高浓度（30 mg·L^-1）PSC和PSN的根表洗脱液中可观察到微塑料，根表吸附可能是导致氧化损伤和生长发育受阻的原因。水稻的芽对微塑料的敏感性远低于根部，芽质量和叶绿素含量受到了一定程度的抑制；3种微塑料均在最高浓度（30 mg·L^-1）时引发了芽的氧化损伤，但各处理组间的差异不大。研究表明，与原始聚苯乙烯微塑料相比，经表面修饰的微塑料，尤其是氨基化微塑料对水稻种子萌发、根系生长和抗氧化系统的负面影响更强。

Effects of polystyrene microplastics on seed germination, growth, and oxidative stress in rice

To examine the effect of microplastics on terrestrial plants, the germination, growth, and oxidative stress of rice exposed to polystyrene microspheres（PS, PSC, PSN）with different surface modifications（original, carboxylated, and aminated）were investigated. The exposure concentrations were 0.2, 1, 5 mg·L^-1, and 30 mg·L^-1. Inhibition of the three microplastics on germination rate and seedling root mass were in the order of PSN＞PSC＞PS, and the suppression of root morphology（root length, root surface area, and root projection area） was generally stronger for the two modified microspheres compared with the original one. Original PS at lower concentrations（0.2 mg·L^-1 and 1 mg · L^-1）stimulated rice roots to increase defensive activity of the antioxidative system, thereby avoiding oxidative stress. With increasing concentration, the antioxidative ability of roots gradually weakened, which resulted in lipid peroxidation at 30 mg·L^-1. However, two surface-modified microplastics led to the inhibition of root antioxidative system at lower concentrations（0.2，1 mg·L^-1）. PSC induced root oxidative stress at the highest concentration（30 mg·L^-1）alone, whereas PSN induced oxidative stress at 1 mg·L^-1. With increasing PSN concentration, oxidative stress was further intensified. Eluted substances from the rice root surface increased significantly with increasing microplastic concentration, which may be associated with the antioxidative reaction in the roots. Microplastics of PSC and PSN were observed in root surface eluates at the highest concentration（30 mg·L^-1）, and the root adsorption may result in oxidative stress and retardation in growth and development. Rice sprout was less sensitive to microplastics than roots, and the sprout weight and chlorophyll content were inhibited to a certain extent. All microplastics led to oxidative stress in sprouts at the highest concentration（30 mg · L^-1）, whereas the differences between various treatments were not significant. The surface-modified microplastics（particularly PSN）exerted stronger negative impacts on rice seed germination, root growth, and antioxidant system compared with the original PS.