Effects Of Different Ammonium Nitrate Ratios On Nitrogen Uptake And Utilization In Roots Of Dwarfing Rootstocks M9T337 And M26 Seedlings

The experiment was conducted in the horticultural experimental station of Shandong Agricultural University,Tai'an,Shandong Province,from 2017 to 2018.The root absorption kinetics of M9T337 seedlings was studied by hydroponic culture in Hoagland nutrient solution with different ammonium nitrate ratios.In addition,¹⁵N isotope tracer technique was used to study the effects of different ammonium nitrate ratios on nitrogen uptake and utilization in roots of M9T337 and M26 seedlings.The main results were as follows:1.The study on root absorption kinetics of M9T337 seedlings under different ammonium nitrate ratios showed that the root activity of T2 treatment?75%NO₃^--N+25%NH₄⁺-N?was the highest and that of total ammonium treatment was the lowest.The absorption kinetics of NO₃^-by M9T337 seedlings showed that the absorption rate of NO₃^-by M9T337 seedlings increased with the increase of nitrogen concentration in solution under different ammonium nitrate ratios.The absorption rate of NO₃^-by T2 treatment was the highest,which was always higher than the other three treatments.With the increase of the ratio of ammonium to nitrogen in nutrient solution,the maximum absorption rate?Vm?and the value of alpha first increased and then decreased,while the value of Michaelis constant?Km?was the opposite.The absorption kinetics of NH₄⁺showed that in the range of 0.05-1 mmol/L,the NH₄⁺uptake rate of M9T337 seedlings treated with different ammonium nitrate ratios continued to increase.When the nitrogen concentration in nutrient solution exceeded 1mmol/L,the absorption rate tended to saturate,and began to decline.T2 treatment was always higher than other treatments.With the increase of ammonium nitrogen ratio in nutrient solution,the values of Vm and alpha decreased,while the values of Km increased.When there is only one form of nitrogen in the nutrient solution,the results are as follows:Km?NO₃^-?<Km?NH₄⁺?,Vm?NO₃^-?>Vm?NH₄⁺?at different nitrogen concentrations.This indicated that when the ratio of ammonium nitrate to ammonium nitrate was 75:25,the maximum absorption rate of M9T337 seedlings was the highest,the ion affinity was the best,and the demand for nitrate nitrogen was higher than that of ammonium nitrogen.2.The effects of different ammonium nitrate ratios on nitrogen uptake and utilization in roots of M9T337 seedlings were as follows:with the increase of ammonium nitrogen in nutrient solution,the utilization rate of ¹⁵N of M9T337 seedlings increased first and then decreased.TherewasnosignificantdifferencebetweenT2treatment?75%NO₃^--N+25%NH₄⁺-N?and T3 treatment?50%NO₃^--N+50%NH₄⁺-N?,but the utilization rate of ¹⁵N was significantly higher than other treatments,and the utilization rate of ¹⁵N was20.41%and 19.77%,respectively.Compared with total ammonium treatment,the total ¹⁵N uptake of seedlings treated with T2 and T3 increased by 129.7%and 113.2%respectively,and the Ndff value of different organs increased significantly.The activity of antioxidant enzymes in leaves of seedlings treated with T2 was always at a high level and gradually increased with the increase of culture time,while that of seedlings treated with total ammonium was at the lowest level;the content of malondialdehyde?MDA?in leaves treated with total ammonium was the highest,and that of seedlings treated with T2 was the lowest.Nitrate reductase activity and glutamine synthetase activity in leaves and roots of M9T337 seedlings could be effectively increased by adding appropriate ammonium nitrogen proportion in nutrient solution,and nitrogen uptake and utilization of M9T337 seedlings could be promoted.The activity of antioxidant enzymes and root morphological indexes were at the lowest level under total ammonium treatment.3.The effects of different ammonium nitrate ratios on root nitrogen uptake and utilization of M26 seedlings were as follows:M26 seedlings were sensitive to ammonium nitrogen concentration in nutrient solution.The utilization rate of ¹⁵N of M26 seedlings treated with 75:25 ratio of total nitrate or ammonium nitrate was significantly higher than that of other treatments,21.99%and 22.93%respectively.The utilization rate of ¹⁵N of M26seedlings treated with total ammonium was the lowest,13.94%.Total nitrate treatment or M2treatment?75%NO₃^--N+25%NH₄⁺-N?could significantly increase root vigor,root tip number,root surface area,root length and leaf SOD,POD,CAT activities of M26 seedlings,and decrease MDA content in leaves.The effect of total ammonium treatment was the worst,root activity and enzyme activities were at the lowest level.