【目的】明确氮沉降背景下硫酸型酸雨酸度变化对杉木(Cunninghamia lanceolata)幼苗根系生理特征的影响,为酸氮沉降区杉木人工林可持续经营管理提供理论依据。【方法】采用1年生杉木幼苗进行盆栽试验,通过模拟不同水平的氮沉降[无氮添加,N0;低氮添加5 g/(m²·a),N1;高氮添加15 g/(m²·a),N2]和酸雨(无酸添加pH为7.0,S0;弱酸添加pH为4.5,S1;强酸添加pH为2.5,S2)处理,研究酸雨和氮沉降对幼苗根系生理和土壤养分变化。【结果】在无氮处理(N0)下,随着硫酸型酸雨pH降低,杉木幼苗根系活力和可溶性蛋白含量显著降低,而根系丙二醛含量、过氧化物酶活性、过氧化氢酶活性及根系生物量显著升高。同样,无酸雨处理(S0)下,氮添加显著降低了根系可溶性蛋白含量,而根系生物量随氮添加量升高而增大。其中,低氮添加对根系活力、丙二醛含量和过氧化氢酶活性不存在显著影响,而高氮添加显著降低根系活力并提升了丙二醛含量以及过氧化氢酶活性。在N1、N2处理下,弱酸处理杉木根系活力和可溶性蛋白含量显著低于强酸处理,其中N1处理下,硫酸型酸雨显著提高根系丙二醛含量、过氧化物酶和超氧化物歧化酶活性;在N2处理下,随着硫酸型酸雨pH降低,根系丙二醛含量和超氧化物歧化酶活性逐渐降低,过氧化物酶活性先降低后升高。此外,硫酸型酸雨和氮添加处理均能降低土壤pH,在弱酸处理中,氮添加显著降低土壤pH,而强酸处理中土壤pH不受氮添加显著影响。仅氮添加时,高氮添加能提高土壤硝态氮和铵态氮含量。低氮(N1)处理下,弱酸处理土壤硝态氮含量最高,显著高于强酸处理;而在高氮(N2)处理中,硫酸型酸雨处理能显著降低土壤硝态氮和铵态氮含量。在无氮(N0)处理中,硫酸型酸雨处理显著降低土壤硝态氮和有效磷含量。【结论】硫酸型酸雨和氮沉降对杉木根系生理特征存在显著的交互作用,虽然我国硫酸型酸雨强度逐渐降低,但轻度酸雨与氮沉降的协同作用仍会加剧土壤酸化,转变低氮沉降对根系生理的有利影响,降低幼苗根系活力,不利于杉木人工林的可持续经营。

【Objective】This study aims to elucidate the effects of sulfuric acid rain acidity on the physiological characteristics of Cunninghamia lanceolata (Chinese fir) seedling roots under nitrogen deposition, providing a theoretical basis for the sustainable management of Chinese fir plantations in acid-nitrogen deposition area.【Method】A pot experiment was conducted using one-year-old Chinese fir seedlings to simulate different levels of nitrogen deposition (no nitrogen addition (N0), low nitrogen addition at 5 g/(m²·a) (N1), and high nitrogen addition at 15 g/(m²·a) (N2))and acid rain (no acid addition (pH 7.0, S0), weak acid addition (pH 4.5, S1), and strong acid addition (pH 2.5, S2)). The experiment investigated the effects of these treatments on seedling root physiology and soil nutrient dynamics.【Result】Under no nitrogen treatment (N0), decreasing pH of sulfuric acid rain significantly reduced root activity and soluble protein content, while increasing root malondialdehyde (MDA) content, peroxidase (POD) and catalase (CAT) activities, and root biomass. Similarly, under no acid rain treatment (S0), nitrogen addition significantly decreased soluble protein content, while root biomass increased with higher nitrogen addition. Low nitrogen addition (N1) had no significant effect on root activity, MDA content, or CAT activity, whereas high nitrogen addition (N2) significantly reduced root activity and increased MDA content and CAT activity. Under N1 and N2 treatments, root activity and soluble protein content were significantly lower in weak acid (S1) than in strong acid (S2) treatments. In the N1 treatment, sulfuric acid rain significantly increased root MDA content, POD, and superoxide dismutase (SOD) activities. Under the N2 treatment, decreasing pH of sulfuric acid rain gradually reduced root MDA content and SOD activity, while POD activity initially decreased and then increased. Additionally, both sulfuric acid rain and nitrogen addition reduced soil pH, with nitrogen addition significantly lowering soil pH under weak acid treatment but showing no significant effect under strong acid treatment. High nitrogen addition alone increased soil nitrate and ammonium nitrogen content (N${\mathrm{O}}_{3}^{-}$-N and N${\mathrm{H}}_{4}^{+}$-N). In the low nitrogen (N1) treatment, weak acid (S1) resulted in the highest soil N${\mathrm{O}}_{3}^{-}$-N content, significantly higher than strong acid (S2). Under high nitrogen (N2) treatment, sulfuric acid rain significantly reduced both nitrate and ammonium nitrogen content. In the no nitrogen (N0) treatment, sulfuric acid rain significantly decreased soil N${\mathrm{O}}_{3}^{-}$-N and available phosphorus content.【Conclusion】Sulfuric acid rain and nitrogen deposition exhibited significant interactive effects on the physiological characteristics of Chinese fir roots. Although the intensity of sulfuric acid rain in China has gradually decreased, the synergistic effect of mild acid rain and nitrogen deposition may still exacerbate soil acidification, reversing the beneficial impact of low nitrogen deposition on root physiology, reducing seedling root activity, and hindering the sustainable management of Chinese fir plantations.