Adaptability Of Juglans Mandshurica Seedlings To Soil Moisture

Juglans mandshurica,one of three major broad-leaved hardwoods in northeast China,turns out a native precious timber source.Except used in urban landscaping,it is widely grown in northeast China as walnut plants.Considerable market demands have indicated its value for cultivation and its importance in economic potentials.The species,mainly growing in northeast and central north of China,prefers humid and fertile humus soil.As rainfall distributes unevenly in the foresaid areas because of greenhouse effect around the globe,water supply has become prominent factor for the growth of Juglans mandshurica.This paper aims to practice an overall study of its demands for water supply during seedling stage to find a solution for an improvement in the drought resistance.To provide theoretical basis for the scientific management and water-efficient cultivation during seedling stage,the growth and physiological response of two different provenances of Juglans mandshurica seedlings under different soil water conditions were studied,and the appropriate concentration of exogenous hormones was applied in this paper.Based on the growth and physiological response of different provenances of Juglans mandshurica seedlings under different soil water content,and the physiological effects of different concentrations of abscisic acid on Juglans mandshurica seedlings,so as to select the most appropriate concentration of abscisic acid treatment to improve the drought resistance of Juglans mandshurica seedlings.The soil water content of Juglans mandshurica seedlings from different provenances were 80-85%(T1),70-75%(T2),60-65%(T3)and 40-45%(T4)of field water holding capacity respectively;in the experiment of exogenous abscisic acid,the concentrations of ABA were 0(CK),2.5(A),5(B),7.5(C),10(D)mg / Lrespectively.The results were as follows:(1)There was no significant difference between the height and ground diameter of the two provenances(P > 0.05)and only the crown diameter of Liaoning provenance.With the increase of soil water deficit,the growth rate of two provenances of Juglans mandshurica seedlings gradually slowed down.At 30 and 60 days of water treatment,there were significant differences between T1 treatment and T3 and T4 treatment.Among them,the net crown increment of Liaoning seedlings in T1 treatment was 146.36% and 199.41% higher than that of T3 and T4 at 30 d,and 111.84% and138.05% higher than that of T3 and T4 at 60 d.By analyzing the growth indexes,it could be seen that when the soil water content of the seedlings was 70～75% and 80～85% of the field water capacity,the leaves grew well,the crown was larger,the seedlings grew well,and the growth speed was faster;when the soil water content was lower than 70～75% of the field water capacity,the growth of the leaves and the crown elongation of the seedlings of the two provenances were inhibited to a large extent.(2)With the extension of soil water control treatment time,the chlorophyll content,catalase(CAT),peroxidase(POD)and soluble protein of the two provenances of Juglans mandshurica seedlings showed a trend of first rising and then declining,while the relative conductivity,soluble sugar and MDA showed a trend of gradually increasing.With the decrease of soil water content,the chlorophyll content of the two provenances decreased gradually,and the superoxide dismutase(SOD),CAT,POD,soluble sugar,soluble protein,relative conductivity and MDA increased gradually.Among them,the SOD activity of Jilin seedlings increased with time,and that of Liaoning seedlings increased first and then decreased;the relative conductivity,MDA and SOD of Jilin provenance seedlings increased rapidly 15 days later than that of Liaoning.When the soil water content is 70～75% and 80～85% of the field water capacity,the soluble sugar and soluble protein of the seedlings of Juglans mandshurica were relatively stable,and the protective enzyme activity could be maintained at a certain level,MDA and relative conductivity increase slowly,indicating that the seedlings of Juglans mandshurica had a good physiological state under this water condition.According to the changes of physiological indexes,it could be seen that Jilin Juglans mandshurica seedlings adapt to a wider range of water than Liaoning,and had a stronger adaptability to the changes of soil water.According to the comprehensive evaluation of the adaptability of the two provenances of Juglans mandshurica seedlings to soil water by the method of membership function,the drought resistance ability of Jilin provenance seedlings was greater than that of Liaoning provenance seedlings.(3)Under the condition of soil water deficit,the relative conductivity and MDA of seedlings sprayed with different concentrations of abscisic acid were significantly lower than those of the control(P < 0.05),and the contents of chlorophyll,soluble sugar,superoxide dismutase(SOD),catalase(CAT)and peroxidase(POD)were significantly higher than those of the control(P <0.05).With the increase of abscisic acid concentration,chlorophyll content,soluble sugar content,SOD,CAT activity of Juglans mandshurica seedlings increased first and then decreased,relative conductivity showed a downward trend,MDA content first decreased and then increased.The relative conductivity,MDA,soluble sugar,SOD,CAT and POD activities of Juglans mandshurica seedlings gradually increased and the chlorophyll content gradually decreased with the increase of soil water content.Spraying 5～7.5 mg/L abscisic acid on the seedlings of Juglans mandshurica could alleviate the effect of water shortage on the seedlings to some extent.