Effects Of Three Types Of Microplastics On Growth And Physiological And Biochemical Characteristics Of Soybean (Glycine Max)

In recent years,the effects of microplastics on agricultural ecosystems have attracted attention from domestic and international scholars.However,research on the ecotoxicological effects of microplastics on plants in agricultural ecosystems is relatively scarce,and only a few relevant studies have been conducted.Soybean is one of the main food crops in China,and there is little research on the toxicity and mechanism of microplastics on it.To explore the toxic effects of microplastics on soybeans,polyvinyl chloride(PVC),polylactic acid(PLA)and polyhydroxybutyrate(PHB)microplastics were selected as test materials,and soybeans as test plants.A combination of water planting and soil culture was used to analyze the effects of different size microplastics PVC,PLA,and PHB on soybean seed germination and seedling growth.The effects of three types of microplastics on the soybean growth and physiological and biochemical characteristics were investigated in terms of seed vitality,plant morphology,photosynthetic pigment content,oxidative stress,and their mechanisms of action were analyzed.The main results are as follows:(1)Through the determination of seed vitality indicators,germination rate,moisture content and relative root length,it was found that PVC-1 and PVC-2microplastics had no significant effect on various indicators of seed vitality,while PLA and PHB microplastics with partial concentrations(50,100 mg/L)had a significant promoting or inhibiting effect on seed vitality.Under various types of microplastics treatment,the seed germination rate and seed vitality indicators showed consistency,and the inhibitory effect of PLA and PHB microplastics was greater than that of PVC microplastics.Similarly,PLA and PHB microplastics have a more significant inhibitory effect on the moisture content of sprouts than PVC microplastics.The effect of microplastics on the relative root length of seedlings is related to their particle size.Under high concentration(200 mg/L),the larger the particle size of PVC and PHB microplastics,the greater their promoting effect on root length.(2)Through the study of the effects of three types of microplastics on the growth and physiological and biochemical characteristics of water planting soybean seedlings,it has found that the microplastic treatments have certain promoting effects on soybean plant height.Compared to PVC and PLA microplastics,PHB microplastics have greater inhibitory effects on plant height(with a significant inhibitory effect on plant height at 200mg/L).Under high concentration treatment with PVC and PLA microplastics,there was a significant inhibitory effect on the fresh and dry weight of aboveground parts,and the root to shoot ratio of soybean plants also significantly increased.The treatment with microplastics had a significant effect on the content of photosynthetic pigments in soybean leaves(p<0.01),and the content of photosynthetic pigments was related to the particle size,categories and concentrations of microplastics.The POD activity in soybean leaves was increased and the CAT activity was inhibited significantly by the treatment of several microplastics.Under high concentration(200 mg/L)of PLA-1 and PHB microplastics treatment,SOD activity was increased.Microplastic treatment can also increase the MDA content in leaves.PLA-2 and PHB microplastics can significantly promote GSH content in leaves,indicating that plants are defending against the peroxidation effect of free radicals on membrane lipids.The effect of PLA and PHB microplastics on soluble protein content is basically manifested as "low to medium concentration inhibition,high concentration promotion".(3)Through the study of the effects of three types of microplastics on the growth and physiological and biochemical characteristics of soil cultured soybean seedlings.The presence of microplastics has a significant inhibitory effect on the emergence rate of soybeans,especially under high concentrations(2%)of PVC-2,PLA and PHB microplastics.Various types of microplastics have promoting effects on plant height and biomass,while PVC-2 and PHB microplastics have no significant changes in main root length.PVC-1,PLA-1and PLA-2 microplastics have promoting effects on main root length.Under various microplastic treatments,the content of photosynthetic pigments shows a trend of increasing firstly and then decreasing with increasing concentration.Under high concentration microplastic treatment,the activity of SOD and CAT was increased significantly,thus promoting the operation of soybean antioxidant system,reducing the accumulation of reactive oxygen species ROS,and reducing external stress and toxicity effects.Under microplastic treatment,the anaerobic respiration intensity was enhanced compared to the control group,and the soluble protein content was increased.Microplastics stimulate the antioxidant defense system by altering enzymatic and non-enzymatic antioxidants,and the antioxidant system responds to stress.This study revealed the effects of microplastics pollution on soybean under soil culture and hydroculture,and provided theoretical basis and reference for ecological risk assessment of higher plants by microplastics.