Effects of Exogenous Melatonin on Gowth,Photosynthesis and Antioxidant System of Cosmos bipinnatus under Microplastic Stress

Yan Hui; Gao Feilong; Zhang Wei; Liu Quanru; Li Wenbin; Qiao Peng

doi:10.14083/j.issn.1001-4942.2025.10.009

Abstract：Using Cosmos bipinnatus Cav.as experimental material and spraying water as control(CK),this study investigated the effects of foliar spraying of 150 μmol/L melatonin(MT)on growth,root architec-ture,chlorophyll content,chlorophyll fluorescence parameters,photosynthetic carbon synthase activity,photo-synthetic characteristics and reactive oxygen metabolism indicators of C.bipinnatus under microplastics(MPs)treatments at 0,0.5,5,50 and 200 mg/kg,in order to elucidate the physiological mechanisms of MT helping C.bipinnatus resist MPs stress.The results were as follows.(1)The treatment of 0.5 mg/kg MPs had a pro-moting effect on the growth of C.bipinnatus,while high concentrations(50,200 mg/kg)of MPs significantly inhibited the growth,and decreased the photosynthetic characteristics and photosynthetic carbon assimilation enzyme activity,while the content of malondialdehyde(MDA)and hydrogen peroxide(H2O2)in the leaves significantly increased.(2)At 0 to 200 mg/kg MPs,compared with CK,under the MT treatment,the total root length,total surface area,total projected area and root tip number of C.bipinnatus increased by 10.6％to 19.5％,9.2％to 28.0％,0.6％to 4.1％and 4.5％to 22.7％,respectively;the chlorophyll a and b contents increased by 11.6％to 35.4％and 5.8％to 24.6％,respectively;the PS Ⅱ actual photochemical quantum effi-ciency(ΦPS Ⅱ),PS Ⅱ effective photochemical quantum efficiency(F′v/F′m)and photochemical quenching coefficient(qP)increased by 3.6％to 27.1％,15.4％to 31.8％and 1.8％to 8.2％,respectively,while the non photochemical quenching coefficient(NPQ)decreased by 52.0％and 19.3％at concentrations of 50 and 200 mg/kg Mps.(3)At 0 to 200 mg/kg MPs,compared with CK,the net photosynthetic rate(Pn),transpi-ration rate(Tr)and stomatal conductance(Gs)in the leaves of C.bipinnatus treated with MT increased by 8.8％to 21.9％,18.6％to 51.2％,and 12.9％to 31.8％,respectively;the activities of ribulose-1,5-diphos-phate carboxylase(Rubisco),cloisone-1,7-diphosphatase(SBPase),fructose-1,6-diphosphate aldolase(FBAase),and transketolase(TKase)increased significantly.(4)Spraying MT under 0 to 200 mg/kg MPs treatment could increase the CAT activity and soluble protein content to varying degrees to reduce MDA and H2O2 content.Compared with CK treatment,spraying MT decreased the MDA and H2O2 contents in C.bipin-natus leaves by 18.5％to 27.6％and 16.4％to 26.3％,but increased the CAT activity and soluble protein content by 10.1％to 21.6％and 8.4％to 26.1％,respectively.In summary,foliar spraying of MT could allevi-ate the adverse effect of MPs and promote C.bipinnatus growth by increasing chlorophyll content in leaves,stimulating antioxidant system function,maintaining chlorophyll fluorescence parameters,enhancing photosyn-thetic carbon assimilation enzyme activity and photosynthesis.