关键词: 氮, 柑橘, 土壤溶液, 铵毒害, 抗氧化系统

Abstract: 【Objective】Through the monitoring of ammonium levels in soil solutions with different pH values, combined with the study on the effects of ammonium levels on the growth and physiological indexes of orange rootstock seedlings, the response process of citrus to ammonium nitrogen (N) was described, which may provide scientific support for the optimal N management of citrus orchard in acid soil. 【Method】 The experiment was designed as a two-factor experiment, with 2 soils as the main treatment and 5 N levels as the secondary treatment. Using acidic yellow soil and alkaline purple soil as the test soil, seedlings of Xiangcheng (junos Sieb. ex Tanaka) were selected as the test material, and five nitrogen levels of 0 (A0), 50 (A50), 100 (A100), 200 (A200) and 400 mg·kg^-1 (A400) were set. The effects of ammonium application level on the concentration of ammonium nitrogen and nitrate nitrogen in soil solution and on the biomass, root morphology, nitrogen absorption, antioxidant system, nitrogen metabolism, MDA content and root activity of citrus were studied. 【Result】 The root length of the citrus with A400 treatment was reduced by 13% when compared with the A0 treatment. And the root vitality was significantly negatively correlated with the ammonium application level. The MDA content of leaves and roots is positively correlated with the ammonium level, which stimulates the oxidative stress response of the roots, especially increases the POD enzyme activity of the leaves. The root, stem, leaf biomass and root-to-shoot ratio of citrus seedlings grown in acid soil were lower than those in calcareous soil. Compared with calcareous soil, the nitrification process in acid soil was slow with  weak nitrification. The NH₄⁺-N concentration and NH₄⁺-N / NO₃^--N in the soil solution of acid soil remained at a higher level at 30 days of the test. Compared with calcareous soil, the total nitrogen accumulation of citrus on acid soil decreased by 17.6%, while the ratio of ammonium to nitrate in leaves and roots increased by 27.2% and 61.1%, respectively.【Conclusion】 In acidic soil, excessive application of ammonium nitrogen caused the accumulation of ammonium nitrogen in soil solution for a long time, resulting in the increase of MDA content , cell membrane damage and nitrogen metabolism disorders and other ammonium toxic phenomena, indicating that ammonium toxicity in citrus is closely related to excessive application of ammonium nitrogen and soil nitrification which is worth paying attention to in terms of production

Key words: nitrogen,  , citrus, soil solution, ammonium toxicity, antioxidant system