Growth And Physiological Responses Of Pinus Koraiensis Container Seedlings To Nitrogen Fertilization In Growing-season And Autumn

Korean pine（Pinus koraiensis）is an important afforestation species in northeast China.Because of the poor natural regeneration of this species,efforts to plant large areas with Korean pine have focused on planting seedlings from nurseries.Fertilization is the necessary step for the seedling cultivation so that optimum fertilization plays a key role in promoting seedling quality.1-year-old(S_1-0)Korean pine container seedlings were used as materials for growing-season fertilization and autumn fertilization,respectively.This research studied the growth performance of Korean pine container seedlings under different fertilization treatments.Combined with root morphology,soluble protein and nutrient concentration,this research elucidated the interaction between growing-season fertilization types and nitrogen levels and autumn fertilization levels,respectively.This research revealed the mechanisms by which growing season fertilization and autumn fertilization affect the growth of Korean pine container seedlings.Results of this research could improve the theory of seedling fertilization and provide a practical fertilization basis for cultivating high-quality Korean pine seedlings in China.The main results of this research were as follows:（1）Growing-season fertilization promoted height and root collar diameter growth of Korean pine container seedlings and increased the accumulation of biomass.All growing-season fertilization treatments increased the Dickson’s quality index except for exponential fertilization with high N level.Conventional fertilization inhibited root growth;seedlings with exponential fertilization had the best root growth at low nitrogen levels;Roots of slow-release fertilizer seedlings were superior to those of CK among three nitrogen levels.（2）Growing-season fertilization improved stress resistance and nutrient concentration of Korean pine container seedlings.Soluble protein concentration increased by21.57%-245.61%,nitrogen concentration increased by 24.29%-43.74%,phosphorus concentration increased by 0.92%-9.93%,and potassium concentration increased by42.62%-146.23%.Nitrogen level is the main factor affecting the growth of Korean pine container seedlings during the rapid growth period.There was a significant interaction between growing-season fertilization type and nitrogen level on root morphology,soluble protein and nutrient concentration of seedlings.（3）Autumn fertilization had no promoting effect on height growth and root collar diameter growth of Korean pine container seedlings.Autumn fertilization decreased height and root collar diameter growth of Korean pine container seedlings,increased biomass by14.80%-300.00%,and increased Dickson’s quality index by 23.81%-353.33%.Autumn fertilization promoted root growth of seedlings,and affected the seedlings of conventional fertilization in growing season more significantly.（4）Autumn fertilization improved frost tolerance and nutrient concentration of Korean pine container seedlings.Soluble protein concentration increased by 10.18%-163.41%,nitrogen concentration increased by 8.66%-27.49%,phosphorus concentration increased by6.52%-37.16%,and potassium concentration increased by 31.06%-230.22%.Autumn fertilization level is the main factor affecting the growth of Korean pine container seedlings during the hardening period.There was a significant interaction between growing-season fertilization type and autumn fertilization level on height,biomass,root morphology,soluble protein and nutrient concentration of seedlings.In conclusion,among different nitrogen levels,there were differences in appropriate growing-season fertilization type of seedlings.Besides,among different growing-season fertilization types,there were differences in appropriate autumn fertilization level of seedlings.Considering the morphological and physiological indexes comprehensively,the suitable growing-season fertilization treatment for Korean pine container seedlings is the application of slow-release fertilizer at medium nitrogen level;the suitable autumn fertilization treatment is autumn fertilization at medium nitrogen level after conventional fertilization in the growing season.