【目的】阐明轻、中、重度火烧区土壤全氮与矿质氮($\mathrm{NH}_{4}{ }^{+}$-N与$\mathrm{NO}_{3}{ }^{-}$-N)供给水平、形态特征及空间格局变化,综合反映兴安落叶松林火烧迹地恢复初期土壤氮营养生境特征,为寒温带针叶林火烧迹地改造与生态恢复提供参考。【方法】在杜香(Ledum palustre)-杜鹃(Rhododendron simsii)-兴安落叶松(Larix gmelinii)林地,以网格法布设固定样地,人工点烧控制林火强度,于火烧前和火烧1 a后采用土钻法采集土样,测定土壤全氮、$\mathrm{NH}_{4}{ }^{+}$-N与$\mathrm{NO}_{3}{ }^{-}$-N含量,计算各指标变化率和各形态氮素比率,并绘制空间格局图。【结果】火烧1 a后:①土壤全氮含量及其变化率呈明显阶段性变化。轻、中度火烧区土壤全氮量升高,全氮量空间格局与火烧强度空间格局相关性不显著,但其变化率格局与之正相关;重度火烧区土壤全氮量下降,全氮量及其变化率空间格局均与火烧强度空间格局负相关。②土壤$\mathrm{NH}_{4}{ }^{+}$-N含量增加。空间上,$\mathrm{NH}_{4}{ }^{+}$-N含量及其变化率空间格局均与火烧强度格局相关性不显著。③土壤$\mathrm{NO}_{3}{ }^{-}$-N含量显著增加。空间上,$\mathrm{NO}_{3}{ }^{-}$-N含量及其变化率空间格局均与火烧强度格局正相关。④土壤供氮形态始终表现为明显的$\mathrm{NH}_{4}{ }^{+}$-N供给优势,但其优势度($\mathrm{NH}_{4}{ }^{+}$-N与$\mathrm{NO}_{3}{ }^{-}$-N的含量比)显著降低,该比值及其变化率的空间格局均与火烧强度空间格局负相关。【结论】大兴安岭北部兴安落叶松林火烧迹地恢复初期,各强度火烧区土壤矿质氮含量与形态变化并未构成原生植被类型恢复的障碍因素;然而,重度火烧区土壤全氮量下降有可能导致长时间尺度上土壤氮供给能力下降。

【Objective】This paper elaborated upon the changes in soil total nitrogen and mineral nitrogen ($\mathrm{NH}_{4}{ }^{+}$-N and $\mathrm{NO}_{3}{ }^{-}$-N) contents, the nitrogen form characteristics and their spatial patterns in lightly, moderately and severely burned areas, which comprehensively reflected the characteristics of soil nitrogen nutrition habitats during the early restoration period of burned forest areas in the Greater khingan Mountains. This study aimed to provide a reference for the renovation and ecological restoration of burned coniferous forests in cold temperate zones.【Method】In the Ledum palustre-Rhododendron simsii-Larix gmelinii forest, fixed sample plots were set up with the grid method, and the intensity of the forest fire was controlled by artificial ignition. Soil samples were collected by auger boring before and one year after burning. The soil total nitrogen, $\mathrm{NH}_{4}{ }^{+}$-N and $\mathrm{NO}_{3}{ }^{-}$-N contents were measured, the change rate of each index and the ratio of mineral nitrogen forms were calculated, and the spatial patterns were drawn.【Result】A year after the burning: (1) Soil total nitrogen content changed, and its change rate was divided into two stages. In the lightly and moderately burned areas, soil total nitrogen content increased. Its spatial pattern was not obviously correlated with the fire intensity spatial pattern, but its change rate spatial pattern was. In the severely burned area, the soil total nitrogen content decreased. The spatial and change rate spatial patterns were both negatively correlated with the fire intensity spatial pattern. (2) Soil $\mathrm{NH}_{4}{ }^{+}$-N content increased in all burned areas; its spatial and change rate spatial patterns were not obviously correlated with the fire intensity spatial pattern. (3) Soil $\mathrm{NO}_{3}{ }^{-}$-N content increased significantly; its spatial and change rate spatial patterns were both positively correlated with the fire intensity spatial pattern. (4) The soil nitrogen form showed evident $\mathrm{NH}_{4}{ }^{+}$-N dominance, but its dominance (the content ratio of $\mathrm{NH}_{4}{ }^{+}$-N to $\mathrm{NO}_{3}{ }^{-}$-N) was reduced. The ratio spatial pattern and change rate spatial pattern were negatively correlated with the spatial pattern of fire intensity. 【Conclusion】During the early restoration period of burned areas in the Larix gmelinii forest, the change in soil nitrogen nutrition habitat did not constitute an obstacle to the restoration of native vegetation types; however, the decline of soil total nitrogen in the severely burned area may bring about the fall-off in nitrogen supply capacity in the long-term.