Effects Of Exogenous Salicylic Acid On Root Growth And Nutrient Uptake Of Apple Under Saline-alkali Stress

Malus hupenensis Rhed.is an excellent apple rootstock,which has strong adaptability to the environment,waterlogging resistance,cold resistance,moisture resistance and salt resistance.In this study,the effects of salicylic acid on root growth and nutrient absorption function of apple were studied in the saline-alkali(120mmol·L^-1mixed saline-alkali)environment.The results were as follows:（1）Under non-saline-alkali condition,0.5 mmol·L^-1,1.0 mmol·L^-1,1.5 mmol·L^-1and 2.0mmol·L^-1salicylic acid were applied to Malus hupenensis Rhed.seedlings by root application and leaf application.Different concentrations of salicylic acid increased the number of lateral roots,lateral root length,lateral root density,total root length,surface area,volume,average diameter and root tip number of the seedlings,and also promoted the absorption of mineral nutrients.When the root application concentration of salicylic acid was 1.0-1.5 mmol·L^-1,the effect of salicylic acid on increasing seedling root growth and nutrient uptake rate was better,and when the leaf application concentration of salicylic acid was 1.5-2.0 mmol·L^-1,the effect of salicylic acid on increasing seedling root growth and nutrient uptake rate was better.Compared with leaf application,root application treatment had more obvious effects on promoting root growth and nutrient uptake of Malus hupenensis Rhed.seedlings and could reduce its usage.（2）Under the mixed saline-alkali stress of 120mmol·L^-1,the lateral root growth,root architecture and nutrient uptake of Malus hupenensis Rhed.seedlings were significantly inhibited.Both root application and leaf application of salicylic acid promoted lateral root growth,improved root architecture parameters and increased nutrient absorption rate,thus alleviating the effect of saline-alkali stress on Malus hupenensis Rhed.seedlings.When root salicylic acid was 0.5-1.0 mmol·L^-1and leaf salicylic acid was 2.0 mmol·L^-1had significant effects on the increase of root growth and nutrient absorption rate under saline-alkali conditions.Root application of salicylic acid alleviated the effect of saline-alkali stress on Malus hupenensis Rhed.seedlings,promoted root growth and nutrient uptake,improved root activity,reduced the accumulation of malondialdehyde and proline,and increased the nutrient content of the plants.（3）Under the mixed saline-alkali stress of 120 mmol·L^-1,root application of different concentrations of salicylic acid had a great effect on root growth,photosynthetic rate,nutrient uptake and soil physical and chemical properties of Fuji apple saplings trees.Results showed that root salicylic acid concentration was 1.0-1.25 mmol·L^-1tendency in the plant root system configurations parameteers,root activity,the contents of nitrate reductase were significantly increased,intercellular CO₂concentrations,and stomatal conductance increased significantly,of young leaf and root of most nutrient content in the salinity-alkalinity stress and other concentration of salicylic acid treatment significantly increased,and reduce the soil p H,soil available phosphorus,urease,ammonium nitrogen,phosphorus and potassium were significantly increased;When the concentration of salicylic acid was 1.5-2.0 mmol·L^-1,the accumulation of MDA and proline was lower than that of other treatments,soil alkali-hydrolytic nitrogen,alkaline phosphatase,nitrate nitrogen,organic matter and available phosphorus were significantly increased,and nitrate reductase was significantly decreased compared with that of saline-alkali stress and other treatments.The results showed that the medium and low concentrations of salicylic acid had significant effects on the growth and nutrient absorption and distribution of plant roots.High concentration of salicylic acid significantly increased soil physical and chemical properties:soil enzyme activity was increased,soil nutrients were activated,and soil nutrients were absorbed by plants.