Effects Of Nitrogen And Phosphorus Fertilization On Photosynthetic Charateristics And Non-structural Carbohydrate Of Various Organs In Fraxinus Mandshurica Sapling

Fertilization is one of the important measures for forest cultivation.Fertilization can affect the non-structural carbohydrate of various organs by changing the nutrient status of trees.However,there is still a lack of understanding about the influence of nitrogen and phosphorus fertilization on the concentration and distribution of non-structural carbohydrates(NSC)in various organs of trees.In this study,15-year-old plantation of Fraxinus mandshurica was selected for 3 years of combined nitrogen and phosphorus fertilization(4 gradients of nitrogen and 3 gradients of phosphate).After fertilization,physiological indicators of Fraxinus mandshurica(net photosynthetic rate,chlorophyll concentration)were measured,NSC(soluble sugar,starch)concentration and nutrient status(N,P)of each organ,analyzed the effects of nitrogen and phosphorus on the physiological characteristics of Fraxinus mandshurica and the NSC concentration and distribution in each organ,the following results are obtained:(1)With the increase of the amount of nitrogen applied,the nitrogen concentration in the leaves of Fraxinus mandshurica increased gradually.The total nitrogen concentration of leaves was the highest under N3P1 treatment,which increased by 39.3%compared with the control(p<0.05).After the fertilization,the concentration of P in the leaves was higher than that of the control.In the N3P2 treatment,the phosphorus concentration of the leaves reached the maximum,which was 38.3%higher than that of the control(p<0.05).The N:P of all treated leaves ranged from 12.62 to 18.40.The N:P reached the highest in the N3P0 treatment,while the N:P was the lowest in the NOP2 treatment.(2)After N and P fertilization,the net photosynthetic rate and total chlorophyll concentration of leaves were higher than those of the control(except N0P1).At the same amount of P,the net photosynthetic rate of leaves increases with the increase of N application.The net photosynthetic rate reached the maximum under the N3P2 treatment,which increased by 39.7%compared with the control(p<0.05).Regardless of the amount of P applied,the concentration of soluble protein in leaves was higher than that of the control when N application reached N2 and N3 levels,and reached the maximum under the N3P2 treatment,which increased 35.2%compared with the control(P<0.05).(3)The concentration of soluble sugar,starch and total NSC in leaves,branches,trunks and thick roots of fertilization treatment of Fraxinus mandshurica were higher than those of the control;In addition,the distribution ratios of soluble sugar and starch in branches and trunks under different fertilization treatment were lower than that of the control;the distribution ratios of starch in leaves and branches were all lower than that of control.N,P fertilization,the concentration of soluble sugar,starch and total NSC in fine roots decreased gradually with the increase of N application rate under the same P application rate.(4)There was a significant positive correlation between leaf N and P concentrations and leaf net photosynthetic rate,and a significant positive correlation between leaf net photosynthetic rate and soluble sugar,starch and total NSC concentration in leaf.This indicated that nitrogen and phosphorus caused the change of NSC concentration by affecting the net photosynthetic rate of leave.There was no significant correlation between the concentrations of N and P in branches and NSC concentrations.P concentration in middle roots was positively correlated with soluble sugar,starch and total NSC in middle roots.There was no significant correlation between N:P and all physiological indexes and NSC concentration.In conclusion,nitrogen and phosphorus fertilization promoted the increase of soluble sugar,starch and total NSC concentrations in leaves by increasing the net photosynthetic rate of leaves,and also led to the increase of total NSC concentrations in branches,trunks,crude roots and medium roots,while the starch and total NSC concentrations in fine roots decreased with the increase of nitrogen application.