Nitrogen Absorption,allocation And Utilization Of Young Dwarf Rootstock ‘Fuji' Apple Trees

Dawarf stock intensive cultivation is a general developing trend of modern apple production in the future.The rootstock is an important inform of apple dawarf stock,whose dawarfing effect is remarkable,and the growth of tree is neat.Besides,it will fruit earlier.One of the reasons that dwarf rootstock unpopularizes in China is the study of cultivation techniques lag behind the practices.The core of young apple trees in cultural management is to ensure vigorously vegetative growth,so it can lay a foundation for productive growth.Nitrogen is the primary element limiting apple growth,which is a component of many organic compounds,such as proteins,nucleic acids,chlorophyll,enzymes,vitamins,alkaloids and hormones.Therefore,the growth,nutrient dynamics and nitrogen absorption,allocation and utilization of two–year–old dawarf rootstock ‘Fuji' apple trees were studied using 15N–labeled tracer method,in order to provide a scientific basis for efficient management techniques of dwarf rootstock apple orchards.The main results were as follows:1.During the period of budbreak and spring shoot growth,the roots grew slowly and their biomass was kept at 17 g/tree,the biomass of the tree also changed a little.However,the biomass of the leaves increased rapidly,with an increase of 166%–219%.Subsequently,both the biomass of roots and tree increased quickly,while the leaves had been growing steadily.In the early stage of defoliation,the dry weight of roots under N0.1(0.1 g/kg)level was 27.24 g/tree,which raised 66.61% and 45.44% compared with N0.2(0.2 g/kg)and N0.3(0.3 g/kg)respectively;the dry weight of tree was 128.23 g/tree,which raised 21.40% and 22.46% compared with N0.2(0.2 g/kg)and N0.3(0.3 g/kg)respectively.The biomass of roots and tree under N0.1 level was still highest in the next year.Consequently,it was N0.1 that could promote young dwarf rootstock apple trees growth.2.The nitrogen,phosphorus and potassium content of new vegetative organs(shoots,leaves)was higher.The duration of spring shoot stop growth and nutrient backflux,nitrogen content of leaves was always high and reduced in the early defoliation.The nitrogen of shoots increased firstly and then decreased,but that of roots and trunk changed a little.In the following year,the nitrogen content of leaves decreased constantly,while roots,rootstock,trunk,branches and shoots declined firstly and then maintained stably.Except for leaves decreasing,the nitrogen accumulation of other organs increased in the early defoliation.The phosphorus and potassium content and accumulation of different organs were similar to those of nitrogen.The quantity of nitrogen,phosphorus and potassium of the whole tree accumulated seldom from bud break to spring shoot grew,which increased gradually from the period of spring shoot grew to early defoliation.In the early stage of defoliation,the amount of nitrogen,phosphorus and potassium accumulation under N0.1 was 2.35 g/tree,0.39 g/tree,1.71 g/tree respectively,which was 1.87 times,2.05 times and 2.19 times separately comparing that of budbreak stage.The amount of nitrogen accumulation increased by 43.29%,14.08% compared with N0.2 and N0.3 respectively;the amount of phosphorus accumulation under N0.1 increased by 34.48%,11.43% compared with N0.2 and N0.3 respectively;the amount of potassium accumulation under N0.1 increased by 18.75%,14.00% compared with N0.2 and N0.3 respectively.The requirement of nitrogen and potassium for apple trees was higher than that of phosphorus.N0.1 was beneficial to the accumulation of nitrogen,phosphorus and potassium in the trees among all treatments.3.The Ndff value of various organs of apple trees increased with the growth period.The Ndff of new vegetative organs aboveground was the highest at spring shoot stop growing stage.From the autumn shoot stop growing stage to early defoliation,the Ndff of roots was the highest and 15 N absorbed by roots was preferential distributed to the new vegetative organs.However,the ability to nitrogen uptake of apple trees was weakened with the increase of nitrogen rates.Furthermore,the nitrogen absorbed by trees could be quickly transported to new organs under N0.1 level at spring shoot stop growth.The 15 N distribution ratio in the leaves was the highest from spring shoot stop growing to nutrient backflux stage.And 15 N distribution ratio of roots under N0.1 treatment(33.76%)was significantly higher than that of N0.2 treatment(17.03%)and N0.3 treatment(22.53%)till the early defoliation,while about 37.65% nitrogen of leaves backflux to fruit trees.The ratio of 15 N utilization increased significantly with the process of growth,and the 15 N amount absorbed by trees from spring shoot stop growing to nutrient backflux stage accounted for 80% or more of the nitrogen uptake during the whole growth periods.The 15 N utilization ratio under N0.1 level was 30.03%,increasing by 7.60% and 38.26% respectively compared with N0.2 and N0.3.The 15 N allocation of fruit trees in the following year was same as that of the first year,but the Ndff value of all organs showed a decreasing trend in the period of a year,and the 15 N absorption rate of trees was less.Nevertheless,the Ndff and 15 N utilization ratio were still highest under N0.1 level.As a result,N0.1 level was beneficial to the nitrogen uptake and utilization of young apple trees.From the above,during the period of budbreak and spring shoot growth,the roots of young rootstock apple trees nearly didn't grow and they seldom absorbed nitrogen.The stored nitrogen of roots,rootstock,trunk and branches transported to leaves to sustain their growth at that time.And then nitrogen absorption capacity gradually strengthened with the rapid growth of roots.In the early defolation,nitrogen of the leaves backfluxed to the storage organs.The biomass and 15 N utilization rate of apple trees under N0.1 were higher than the other treatments,so it was N0.1 that could promote young apple trees growth and nitrogen absorption.