The Research On Alleviating Effect Of Two Exogenous Hormones On Senna Corymbosa Under Strong Alkali Stress

Senna corymbosa is a semi-evergreen shrub that is widely used in gardens because of high ornamental value and strong adaptability.In order to apply S.corymbosa in the ecological remediation of soil contaminated by seepage under red mud,1-year-old S.corymbosa was used as the test material.NaOH aqueous solution was used to simulate strong alkali stress,and 6 treatments with different concentrations and controls were set to determine the morphological characteristics,growth and physiological indexes of S.corymbosa were determined,and the most suitable growth and the strongest alkali concentration with the highest tolerance were screened out.Based on the strong alkali stress test,NaOH aqueous solution was used to simulate severe strong alkali stress,and different concentrations of Melatonin(MT)and Gibberellin(GA3)and their suitable concentrations were sprayed on the foliar surface.It’s morphological characteristics and growth physiological indexes were determined,the optimal concentration of two exogenous hormones to alleviate strong base stress and the most suitable concentration ratio for alleviating strong base stress when combined were explored,the response of S.corymbosa to exogenous hormone administration during strong base stress was explored,and its alkali resistance was comprehensively evaluated by correlation analysis and principal component analysis.The main results are as follows:(1)The results showed that S.corymbosa grew well under the stress treatment of alkali concentration≤25 mmol·L-1,and all indicators could maintain a high level of resistance to the damage caused by strong alkali stress.But the indexes of S.corymbosa decreased significantly and the growth status was significantly inhibited under the alkali concentration≥100 mmol·L-1,The plant cell damage was serious and the light energy utilization rate was greatly reduced.S.corymbosa can withstand a maximum alkali concentration of 325 mmol·L-1。(2)Sprayed 5 concentrations of melation solution on leaves under under severe strong alkali stress of 325 mmol·L-1,the results showed that foliar spraying of 200μmol·L-1 MT to S.corymbosa,the light energy capture capacity was significantly improved and the content of malondialdehyde was significantly reduced,while SOD activity and osmoregulatory substances increased significantly.It was indicated that the appropriate MT concentration could alleviate the stress of S.corymbosa and promote the growth of S.corymbosa seedlings.(3)Sprayed 5 concentrations of gibberellin solution on leaves under under severe strong alkali stress of 325 mmol·L-1,the results showed that foliar spraying of 200mg·L-1 GA3 to S.corymbosa,the osmomodulator,antioxidant enzyme activity and relative water content of S.corymbosa were significantly improved.While the absorption,transmission of light energy in the photoreaction center were significantly improved,and the content of malondialdehyde significantly reduced.That’s promotes the growth of S.corymbosa plants and improves the alkali resistance of seedlings.(4)Foliar spraying with different concentrations of exogenous hormones can enhance the alkaline tolerance of S.corymbosa.The combination treatment of MT at 200 μmol·L-1 and GA3 at 200mg·L-1 could significantly reduce the alkaline content and malondialdehyde content of S.corymbosa under strong alkali stress,and improve the growth indexes such as plant height and ground diameter growth.The content of antioxidant enzyme activity and osmomodulating substances reached the highest,and the utilization rate of light energy was significantly improved.It was indicated that the combination of hormones could well promote the growth of S.corymbosa seedlings under strong alkali stress,and was conducive to the accumulation of dry matter of plants.(5)S.corymbosa shows strong tolerance to strong alkaline soils.We can try to promote the planting of S.corymbosa to the corresponding red mud polluted areas and strong alkaline soil areas(the concentration of soil leaching solution is not higher than 325 mmol·L-1),priority should be given to planting in strongly alkaline soils such as red mud polluted areas to improve environmental quality.At the same time it can also be extended to industrial areas where there is a risk of strong alkaline pollution exceeding the standard,such as chemical plants,for planting hedges and green walls to achieve better ecological and landscape effects.In summary,spraying 200 μmol·L-1 melatonin during planting and 200 mg·L-1 gibberellin can effectively improve the survival rate of plants,reduce the degree of damage to S.corymbosa plants under strong alkali stress,and improve the alkali resistance ability of S.corymbosa.The administration of different combinations of exogenous hormones can effectively increase the alkali tolerance of S.corymbosa,and the spraying of exogenous hormones presents a good development and application prospect in the field of improving the alkali tolerance mechanism of ornamental shrubs.