聚苯乙烯微塑料对典型农作物种子发芽和幼苗生长的影响

Impacts of Polystyrene Microplastics on Seed Germination and Seedling Growth of Typical Crops

微塑料在农业土壤中可直接或间接地影响作物生长,而种子发芽和幼苗生长初期是作物生理毒性的敏感阶段。为认识微塑料对典型农作物的生理毒性,选用5μm聚苯乙烯微塑料(5μm-MPs),通过7 d种子发芽试验和33 d土培观测其对中国几种典型农作物种子发芽及幼苗生长的影响。0—100 mg·L^(-1)5μm-MPs水培试验结果表明,5μm-MPs对小麦(Triticum aestivum)、玉米(Zea mays)、谷子(Setaria italica)、花生(Arachis hypogaea)、向日葵(Helianthus annuus)等5种作物种子的平均发芽时间均无显著影响,对小麦、玉米、向日葵、谷子的种子发芽能力和种子活力无显著影响,但花生种子对5μmMPs敏感,指标受到显著抑制,且5μm-MPs质量浓度越大抑制越强。以玉米、小麦、花生为例,0—100 mg·kg^(-1)5μm-MPs土培试验结果表明,部分处理5μm-MPs对3种作物幼苗生长表现出一定的抑制作用。种植15 d时各处理5μm-MPs均显著抑制小麦幼苗株高,但种植30 d时5μm-MPs对3种作物幼苗株高均无显著影响。各处理5μm-MPs对小麦和玉米叶片叶绿素总含量未表现出一致的显著影响趋势,对两者叶片叶绿素a的抑制作用均强于叶绿素b,且可显著诱导小麦、玉米叶片超氧化物歧化酶活性下降,20 mg·kg^(-1)5μm-MPs处理与对照组相比分别下降了35.5%和50.6%。含5μm-MPs土壤的氮含量在种植后显著增加,而小麦、玉米幼苗叶面氮含量在不同生长时期均偏低,抑制植物吸收、转运土壤中的氮元素是5μm-MPs影响作物幼苗生长的可能机制。

Microplastics can affect crop growth in agricultural soil directly or indirectly,and seed germination and early seedling growth of crops are the sensitive stages of physiological toxicity.To understand the physiological toxicity of microplastics to typical crops,the effects of 5μm polystyrene microplastics(5μm-MPs)on seed germination and seedling growth of several typical crops in China were observed through a 7-day seed germination experiment and 33-day soil culture.The results of hydroponic culture with 5μm-MPs mass concentration in the range of 0–100 mg·L^(-1)showed that 5μm-MPs had no significant effect on the average germination time of the seeds of five crops such as wheat(Triticum aestivum),corn(Zea mays),millet(Setaria italic),peanut(Arachis hypogaea)and sunflower(Helianthus annuus),and had no significant effect on the germination ability and seed vitality of the seeds of wheat,corn,sunflower and millet,but peanut seeds were sensitive to 5μm-MPs with the above indexes significantly inhibited,and the greater the mass concentration,the stronger the inhibition.Taking corn,wheat and peanut as examples,soil culture with 5μm-MPs mass fraction in the range of 0–100 mg·kg^(-1)showed that 5μm-MPs had a certain inhibitory effect on the seedling growth of the three crops under some experimental conditions.On the 15th day of planting,all mass fractions of 5μm-MPs significantly inhibited the height of wheat seedlings,but on the 30th day of planting,5μm-MPs had no significant effect on the height of seedlings of the three crops.All mass fractions of 5μm-MPs did not show a consistent significant influence on the total chlorophyll content of wheat and corn leaves.The inhibitory effect on chlorophyll a of both leaves was stronger than that on chlorophyll b,and could significantly induce the decline of superoxide dismutase activity in wheat and corn leaves.At the 5μm-MPs mass fraction of 20 mg·kg^(-1),the superoxide dismutase activity in wheat and corn leaves decreased by 35.5%and 50.6%,respectively,compared with the control group.The nitrogen content of 5μm-MPs-bearing soil increased significantly after planting,while the leaf nitrogen content of wheat and corn seedlings was low at different growth stages.Inhibiting plants from absorbing and transporting nitrogen in soil was the possible mechanism of the influence of 5μm-MPs on the growth of crop seedlings.