Effects Of Nitrogen On Root Morphology And Respiration Rate Of Walnut Seedlings Under Pot Conditions

Nitrogen(N)is an important nutrient element necessary for the growth and development of walnut(Juglans regia),and its absorption and utilization efficiency have an important effect on the growth and development of walnut.At present,the effects of N supply on root morphology,root N uptake and root respiration of walnut seedlings are not very clear.In this study,3-year-old walnut seedlings were taken as the research object,based on the experiment of controlled N application under pot condition,with the help of technical means such as whole plant root excavation,instrumental determination and laboratory chemical analysis,the method of mathematical statistical analysis was adopted.The dynamic changes of root morphological characteristics such as root length,root surface area,root volume and its total N content,respiration rate,and the effects of root diameter,N dose and N form on root morphological characteristics,total N content and respiration rate of walnut seedlings were analyzed.The main results were as follows:Both N dose and N form had significant effects on root morphological characteristic parameters(P<0.05).With the passage of time,the characteristic parameter values of root morphology gradually increased,and with the increase of N dose,there was an obvious superposition effect on the characteristic parameter values of root morphology.When ammonia nitrogen(NH4+-N)and nitrate nitrogen(NO3--N)were applied at the same time and the ratio was 50%,the characteristic parameter values of root morphology were the largest,which was the most suitable for root growth.Both N dose and N form had signficant effects on root total N content(P<0.05).The total N content of roots of three grades(diameter ≤1mm,1mm<diameter ≤ 2mm and diameter>2mm)decreased gradually with the passage of time,and the smaller the root diameter was,the higher the total N content was.The increase of N dose could effectively slow down the decline of root total N content with the passage of time.When NH4+-N and NO3--N were applied simultaneously and the ratio was 50%,the root total N content was the highest.The effect of N dose on root respiration rate was significant(P<0.05),but the effect of N form on root respiration rate was not significant(P>0.05).The root respiration rate increased at first and then decreased with the passage of growing time,and reached the maximum in August.The surface respiration rate increased with the increase of diameter,while the specific root respiration rate decreased with the increase of diameter.With the increase of N dose,the root respiration rate increased gradually,and the root respiration rate reached the maximum when NH4+-N and NO3--N were applied simultaneously.The results suggested that increasing N supply could promote root growth,root N uptake and root respiration of walnut seedlings.50%of NH4+-N and NO3--N were the best ratio of N form.Simultaneous application of NH4+-N and NO3--N,can contribute to the root growth and N absorption and utilization of walnut seedlings,which has a certain guiding significance in walnut seedling cultivation,young tree fertilization and soil nutrient management.