The Action Mechanism Of AgNPs On Phytoplankton And Hydrophyte

The widespread use of AgNPs will inevitably lead to the release of it into the surrounding environment.At this time,the water ecosystem is one of the important gathering places for the release of AgNPs to the natural environment.Therefore,the continuous accumulation of AgNPs in the aquatic environment has also brought varying degrees of impact on aquatic organism.Algae is the primary producer of water,and aquatic plants are also one of the most important components in the water ecosystem.Both of them have played a vital role in maintaining the stability of the water ecosystem.Therefore,the effect of AgNPs on its growth is also very important for its successful colonization and the effect of aquatic ecosystem restoration.In this study,several Freshwater algae and aquatic plant Acorus calamus were selected.Through a comparative study of the physiological response of Microcystis aeruginosa and Selenastrum capricornutum to AgNPs,the physiological mechanism of the different tolerances of the two algae to AgNPs was revealed.To evaluate the toxic effects of AgNPs on Acorus calamus through the effects of AgNPs on the growth,physiology and photosynthetic system.The main research contents and results are as follows:(1)AgNPs have a certain degree of toxic effect on several freshwater algae tested,of which M.aeruginosa and Anabaena flos-aquae,The green algae:S.capricornutum,Chlorella pyrenoidosa,Chlorella vulgaris and Scenedesmus obliquus are slightly more tolerant than cyanobacteria.Among the green algae,the semiinhibitory concentration of S.capricornutum is the lowest and the most sensitive.(2)AgNPs can cause serious oxidative stress to M.aeruginosa,and also reduce its photosynthetic efficiency and increase its extracellular polysaccharide content.AgNPs can also cause the increase of ROS in cells of S.capricornutum,decrease the photosynthetic efficiency,and increase the content of extracellular polysaccharide.The secretion of algae can also affect the particle size of AgNPs and promote the aggregation of AgNPs particles.(3)The comparative analysis of the physiological response mechanism between M.aeruginosa and S.capricornutum showed that although the ROS content in the cells of the two algae increased,the accumulation sites were not the same.The main ROS accumulation site of M.aeruginosa is on the photosynthetic electron chain,while the ROS accumulation site of S.capricornutum is on the electron transport chain of mitochondria.AgNPs can significantly inhibit the photosynthetic efficiency of the two algae.At the same dose of inhibition rate,the damage of photosynthetic system of M.aeruginosa increased gradually with time,while that of S.capricornutum decreased first and then increaed gradually.In addition,although S.capricornutum and M.aeruginosa both produce a lot of EPS to resist the stress of AgNPs.S.capricornutum mainly prevents the entrance of AgNPs by secreting more CPS and M.aeruginosa can secrete more RPS to promote the reunion of AgNPs in solution to reduce its biological toxicity.(4)AgNPs also show a certain growth inhibitory effect on Acorus calamus.Compared with the control group,plant fresh weight and root length were significantly inhibited after 20 days exposured to AgNPs.The increase of ROS level and the activity decrease of root cell caused by AgNPs stress.AgNPs also reduced the chlorophyll content of plant leaves and inhibited photosynthesis?Through the fast phase analysis of chlorophyll fluorescence of Acorus calamus,the results show that the decrease of photosynthetic efficiency is mainly due to the inhibition of photosynthetic chain and the obstruction of electron transfer.