聚苯乙烯微塑料对黑藻生长及生理生化特征的影响

Effects of polystyrene microplastics(PS-MPs)on the growth,physiology,and biochemical characteristics of Hydrilla verticillata

为探讨淡水环境中微塑料的污染对沉水植物产生的生理生化影响,选择典型沉水植物黑藻为供试材料,以粒径3μm的聚苯乙烯微塑料颗粒(PS-MPs)为外源胁迫污染物,通过添加不同浓度的PS-MPs(5、10、30、50、100 mg·L^(-1))设置不同暴露组及对照组,测定沉水植物的株高、生物量、叶绿素含量、抗氧化酶活性、光合荧光参数及荧光成像的变化特征。结果表明:50~100 mg·L^(-1)PS-MPs下黑藻的株高显著下降;较低浓度下(如5 mg·L^(-1))黑藻的鲜重显著升高,但随着PS-MPs暴露浓度进一步增加,黑藻鲜重降低,干重无显著变化。黑藻叶绿素总量、叶绿素a和叶绿素a/b均随PS-MPs浓度的增加呈显著下降趋势,叶绿素b无明显变化。PS-MPs处理下超氧化物歧化酶(SOD)、过氧化氢酶(CAT)和过氧化物酶(POD)活性均随胁迫浓度的增加呈先上升后下降的趋势,叶绿素荧光参数(Fo、Fm、Fv/Fm)均呈下降趋势,而稳态下的PSⅡ反应中心关闭程度(1-Qp-Lss)总体呈上升趋势,这可能与PS-MPs抑制黑藻PSⅡ反应中心有关。黑藻的荧光成像强度随PS-MPs浓度的增加而降低,在PS-MPs浓度为10 mg·L^(-1)及以下时,黑藻叶片表现出正常的光合活性;当PS-MPs为30 mg·L^(-1)及以上时,叶片边缘的光合强度小于茎秆及其周边,叶片呈现发黄、残叶等现象。推测黑藻基本能适应低浓度PS-MPs(0~30 mg·L^(-1))的污染水域,而在PS-MPs高于30 mg·L^(-1)的污染水域中其生长和光合作用将受到抑制。

In order to evaluate the effects of polystyrene microplastics(PS-MPs)on the growth,physiology,and biochemical characteristics of submerged plants,we exposed a typical submerged plant,Hydrilla verticillata,to a series of concentrations(i.e.0,5,10,30,50,100 mg·L^(-1))of 3μm polystyrene microplastics(PS-MPs)and measured parameters including height,biomass,chlorophyll content,antioxidant enzyme activity,photosynthetic fluorescence.The results showed that the height of H.Verticillata significantly decreased at the high PS-MP concentrations(50 to 100 mg·L^(-1)),while the fresh weight significantly increased at the low PS-MP concentration(5 mg·L^(-1)).The fresh weight of H.verticillata gradually decreased with the increasing PS-MP concentration but the dry weight did not change.The total amount of chlorophyll,chlorophyll a,and chlorophyll a/b significantly decreased with the increases of the PS-MP concentrations,while the chlorophyll b did not change.PS-MPs affected the antioxidant enzyme activities of H.verticillata.The activities of superoxide dismutase(SOD),catalase(CAT)and peroxidase(POD)were first increased and then decreased with the increasing PS-MP concentration.The chlorophyll fluorescence parameters(Fo,Fm,Fv/Fm)decreased with the increasing concentration of PS-MP and the 1-Qp-Lss value(reflective of the closing of PSⅡreaction center)was increased under the stable state,probably due to the inhibited PSⅡreaction center.The overall intensity of fluorescence imaging of H.verticillata decreased with the increasing concentration of PS-MPs.When the PS-MP concentration was lower than 10 mg·L^(-1),the photosynthetic activity of the leaves was normal.In contrast,when the PS-MP concentration was higher than 30 mg·L^(-1),it caused significant adverse effects on leaves,including weaker photosynthetic intensity and the presence of yellow or withered leaves.Our results suggested that H.verticillata could tolerate PS-MP pollution but its growth and photosynthesis would be inhibited at high concentrations(>30 mg·L^(-1)).Our results provided basic information to better understand the eco-physiological effects of PS-MPs in the freshwater environment.