Ecotoxicological Effects Of Glyphosate On Myriophyllum Aquaticum And Trapa Bispinosa,and Mitigation Effect Of Salicylic Acid

Glyphosate is widely used worldwide because of its wide range of herbicides,its ability to absorb and conduct in plants,and its difficulty in the evolution of resistance to plants.The detection rate of glyphosate residues in water is high,which may affect the normal physiological and biochemical processes of aquatic organisms and bring risks to aquatic ecosystems.When plants are stressed by pollutants,the addition of exogenous salicylic acid can significantly alleviate the symptoms of plant poisoning and improve their tolerance under such stress conditions.Salicylic acid,a phytohormone,plays an important role in multiple metabolic activities of plants as secondary metabolites.On the other hand,there are many studies show that exogenous salicylic acid has detoxified effects on various pollutant stresses.At present,there are few studies on the physiological responses of aquatic plants to glyphosate,and there is no research to investigate the addition of exogenous salicylic acid to the glyphosate environment to discuss their interaction with plants and whether salicylic acid has a mitigating effect to glyphosate poisoning.In this paper,the aquatic plant Myriophyllum aquaticum and Trapa bispinosa were selected as the research objects,and their physiological and biochemical responses after 14 days of treatment were studied by hydroponic method in different doses of glyphosate environment(0,0.05,0.1,0.3 mmol/L).At the same time,this paper also studied how the effects of different concentrations of salicylic acid(0,0.2,0.4,0.8 mmol/L)on the two plants under the above stress conditions can alleviate the toxicity of glyphosate.The research results are as follows:1.Glyphosate significantly inhibited the growth of M.aquaticum,and its relative growth rate decreased by 12.72%?15.42%compared with the control group.In the photosynthesis system,the content of chlorophyll a and chlorophyll b of the plants significantly decreased under the stress of 0.3 mmol/L glyphosate,while the carotenoids did not show significant differences.2.The low concentration of glyphosate has hormesis on the growth of T.bispinosa.In the 0.05 mmol/L glyphosate environment,the relative growth rate of plants is significantly increased,but this effect disappears with the increases of glyphosate concentration and inhibit its growth under 0.3 mmol/L glyphosate.The photosynthetic pigment content in plants is consistent with growth.Glyphosate caused great damage to the cell membrane lipid of T.bispinosa.In the concentration range set by this experiment,the plant MDA content increased significantly compared with the control group,and the antioxidant enzyme activity was also significantly affected.3.The low concentration of single salicylic acid added significantly promoted the growth of M.aquaticum,and the relative growth rate increased to 5.13 times compared to the control group.Under the condition of low concentration of glyphosate,the addition of exogenous salicylic acid can alleviate its inhibitory effect on plant growth,and the best effect was observed when 0.2 mmol/L salicylic acid was added,compared with the control group.The relative growth rate increased to 23.35.When the concentration of glyphosate is not less than 0.1 mmol/L,?0.4 mmol/L salicylic acid can alleviate the inhibition on plant growth.The contents of MDA and H₂O₂were not significantly different under single salicylic acid treatment,and the alleviation effect of salicylic acid on glyphosate stress was only observed under 0.05mmol/L glyphosate+?0.4 mmol/L and 0.1 mmol/L glyphosate+?0.4 mmol/L.In the same glyphosate background,the addition of salicylic acid stimulated the increase of APX activity in plants and reached the maximum at 0.4 mmol/L.4.The medium to high concentration of salicylic acid significantly inhibited the growth of T.bispinosa,and the addition of salicylic acid eliminated the toxic stimulating effect of glyphosate,especially 0.8 mmol/L of salicylic acid added causes plant death directly.Similar to the growth response,0.8 mmol/L salicylic acid caused a significant decrease in the photosynthetic pigment content of plants.Exogenous salicylic acid did not alleviate the decrease in the pigment content caused by glyphosate.Under the stress of 0.05 mmol/L glyphosate,the addition of exogenous salicylic acid added could significantly reduce the MDA content and alleviate the degree of cell membrane lipid damage.This may be mainly contributed by the significantly increase of SOD activity.When the concentration of glyphosate in the environment is?0.1 mmol/L,the addition of salicylic acid can significantly increase the activity of CAT and APX to make the contnet of H₂O₂more stable.After treatment with single salicylic acid,the soluble protein content of T.bispinosa did not make significant difference.Under the stress of glyphosate,the addition of exogenous salicylic acid significantly increased the content of soluble protein and proline.Our results indicate that:1.Glyphosate in the selected concentration range of the experiment significantly inhibited the growth of M.aquaticum,and the content of chlorophyll a and chlorophyll b in the plant also decreased significantly under high concentration conditions.However,after adding glyphosate,it showed a completely different physiological response on T.bispinosa.The low concentration of glyphosate has hormesis on the growth and the photosynthetic pigment content in the plant.At the same time,its antioxidant system showed higher sensitivity to the addition of glyphosate,and the MDA content increased significantly.The antioxidant enzyme content was also greatly affected.2.Under the stress of 0.05 mmol/L glyphosate,the addition of exogenous salicylic acid could alleviate the growth inhibition of M.aquaticum,and the best effect was obtained at 0.2 mmol/L.Under the conditions of glyphosate treatment,the APX activity increased significantly after the addition of salicylic acid to alleviate the cell damage caused by glyphosate,and the maximum value was observed at 0.4mmol/L.Unlike M.aquaticum,the single addition of 0.4?0.8 mmol/L salicylic acid significantly inhibited the growth of T.bispinosa.Under the stress of glyphosate,0.8mmol/L salicylic acid caused the death directly.The addition of salicylic acid to 0.05mmol/L glyphosate condition can reduce the damage of cell membrane lipid by increasing the activity of SOD and decreasing the content of MDA.Salicylic acid was added to the water of 0.1 mmol/L glyphosate,and the activity of CAT and APX was significantly improved,the content of H₂O₂was stable.As to the non-enzymatic antioxidant system,the content of soluble protein and free proline increased significantly,which can alleviate the ecotoxicological effects of glyphosate on T.bispinosa.