摘要: 目的分析河北省平泉县火烧迹地油松天然次生林的土壤氮在火后不同年份的变化特征，结合林分因子、立地因子和可燃物因子，研究土壤氮变化的影响因素，为火烧迹地养分循环研究及恢复提供科学依据、�/sec> 方法选取河北平泉县柳溪镇油松林火烧迹地为研究对象，分别于2015年（火后当年）�?016年（火后1年）�?021年（火后6年）采集土壤样品，测定土壤全氮（TN）、碱解氮（AN）、铵态氮（NH ₄ ⁺-N）和硝态氮（NO ₃ ∑�/sup>-N）含量，比较和分析上�?种氮含量在不同火强度（轻度火烧、中度火烧、重度火烧、对照样地）、不同土层深度（0 ~ 10 cm�?0 ~ 20 cm）在不同年份�?015�?016�?021年）的变化趋势。使用相关性分析和冗余分析探究林分因子（树高、胸径、郁闭度）、立地因子（坡度、坡向）和可燃物因子�?�?0�?00 时滞可燃物载量�?�?0�?00 时滞可燃物含水率）对土壤氮元素的影响、�/sec> 结果�?）整体而言，火强度、土层深度、年份对4种土壤氮含量具有显著影响＇�i>P< 0.05），火强度和土层深度�?015年的4种土壤氮含量存在交互作用＇�i>P< 0.05），火强度和年份�?种土壤氮含量存在交互作用＇�i>P< 0.05），火强度、土层深度和年份对土壤氮含量不具有三因素交互影响＇�i>P> 0.05）；�?）火�?年（2016）土壤全氮、铵态氮、硝态氮含量回升，以重度火烧样地最为明显，增幅分别�?64.67%�?97.97%�?85.63%，碱解氮含量降低，中度样地降幅为52.48%。火�? 年（2021）土壤全氮、铵态氮、碱解氮含量在中度样地回升明显，增幅分别�?68.78%�?09.00%�?27.51%，硝态氮含量在中、低强度下降，降幅为14.31%�?4.34%；（3）RDA结果表明，可燃物含水率对土壤氮含量的变化贡献最多解释度�?时滞可燃物含水率影响碱解氮含量，并与其成正比关系�?00时滞可燃物含水率影响硝态氮含量，并与其呈正比关系。林分因子和立地因子对土壤氮含量变化解释度较小，主要是间接作用、�/sec> 结论火后6年内土壤氮含量的变化先降低再回升，这是火强度、土壤和年份共同作用的结果。火烧初期（火后当年�?年），火强度对土壤氮含量的影响起主导作用，但是随着年限增加�?年），火强度对土壤氮含量的直接影响降低，火强度与土壤的介导作用，通过土壤含水率、温度、pH等指标继续影响土壤氮含量的变化。火烧迹地植物的更新与发育同样受到介导作用影响，不同生长阶段的养分利用策略差异，以及植被凋落物的累积也是土壤氮含量在火后1年和6年发生明显变化的重要原因、�/sec>

关键诌�
• 土壤养分配置/
• 土壤氮元紟�/a> /
• 火烧迹地恢复/
• 油松枖�/a>

Abstract: ObjectiveThe variation characteristics of soil nitrogen of Pinus tabuliformisnatural secondary forest in Pingquan County, Hebei Province of northern China were analyzed in different years after fire, and the influencing factors of soil nitrogen were explored in combination with stand factors, site factors and fuel factors, so as to provide a scientific basis for nutrient circulation and vegetation restoration after fire. MethodStudy sites were burnt areas located in Liuxi Town of Pingquan County. Soil samples were collected in 2015(the year after the fire, 0 year), 2016 (1 year after the fire, 1 year) and 2021 (6 years after the fire, 6 years), respectively. We analyzed the tendency of content of soil total nitrogen (TN), alkali-hydrolysable nitrogen (AN), ammonium nitrogen (NH ₄ ⁺-N) and nitrate nitrogen (NO ₃ ^{∑�/sup>-N) under different years (0 year, 1 year and 6 years), different fire intensities (CK, control test plots which is unburnt area; L, low intensity burnt area; M, moderate intensity burnt area; H, heavy intensity burnt area), and different soil layers (0�?0 cm and 10�?0 cm). Correlation analysis (Pearson) and redundancy analysis (RDA) were used to explore the potential impact of stand factors (tree height, DBH, canopy density), site factors (slope position and slope gradient) and fuel factors (1 h, 10 h, 100 h fuel load, 1 h,10 h,100 h fuel water content) on soil nitrogen.} Result(1) Fire intensity, soil layer and years had significant influence on 4 types of soil nitrogen ( P< 0.05). Fire intensity and soil layer had an interaction with all kinds of soil nitrogen ( P< 0.05) in 2015. Fire intensity and years had an interaction with all kinds of soil nitrogen ( P< 0.05). Fire intensity, soil layer and years showed no three-factor interaction with all kinds of soil nitrogen ( P> 0.05). (2) Total nitrogen content, ammonium nitrogen content and nitrate nitrogen content increased in 2016 (1 year), especially in heavy intensity areas (H), and the amplification was 464.67%, 397.97%, 185.63%, respectively. But alkali-hydrolysable nitrogen content decreased in each sample plot, especially in M-plot (52.48%). Total nitrogen content, ammonium nitrogen content and alkali-hydrolase nitrogen content increased in 2021 (6 years), especially in moderate intensity areas (M), and the amplification was 368.78%, 209.00%, 427.51%, respectively. But nitrate nitrogen content decreased by 14.31% and 14.34% in low intensity areas (L) and moderate intensity areas (M), respectively. (3) RDA results showed that fuel water content had the most contribution to the change of soil nitrogen content. 1 h fuel water content had an effect on alkali-hydrolase nitrogen content. 100 h fuel water content had an effect on nitrate nitrogen content. Both of them had a positive relationship between fuel factors and soil nitrogen. Stand factors and site factors had little explanatory on soil nitrogen content, which was the indirect effect. ConclusionThe change of soil nitrogen content decreases first and then raises up, which is the common action with fire intensity, soil and years. At the early stage after burning (2015, 0 year; 2016, 1 year), fire intensity plays a significant role in affecting soil nitrogen content. However, the influence power of fire intensity decreased in 2021 (6 years). The direct impact of fire intensity on soil nitrogen content is reduced, and the mediation between fire intensity and soil continues to affect the change of soil nitrogen content through soil moisture content, temperature, pH and other indicators. The regeneration and development of vegetation in burnt areas is also affected by mediating effects. The differences in nutrient utilization strategies at different growth stages and the accumulation of vegetation litter are also important reasons for the significant changes of soil nitrogen content in 1 year and 6 years after fire.

Key words:
• soil nutrient allocation/
• soil nitrogen element/
• restoration of burned area/
• Pinus tabuliformisforest

�?nbsp; 1不同年份土壤氮含量变匕�/p>

CK代表对照样地，L代表轻度火烧样地，M代表中度火烧样地，H代表重度火烧样地，不同颜色柱形代表不同年份。在同一年份下，相同字母表示不同火强度土壤氮含量差异性不显著，不同字母代表差异性显著。下同。CK means controlled sample plots, L means light burned sample plots, M means moderate sample plots, H means heavy/severe sample plots, and different color columns represent different years. In the same year, the same letter means that the difference of soil nitrogen content with different fire intensities is not significant, different letters mean the difference is significant. The same below.

Figure 1.Changes of soil nitrogen content in different years

下载: 全尺寸图牆�/a> 幻灯牆�/a>

�?nbsp; 2土壤氮元素和林分因子、立地因子、可燃物因子的相关性矩阴�/p>

TN.全氮；NH₄⁺-N.铵态氮；NO₃^{∑�/sup>-N.硝态氮；AN.碱解氮；TH.树高；Ccover.郁闭度；Slope.坡度；Position.坡位；m1h、m10h、m100h�?�?0�?00时滞可燃物含水率；l1h、l10h、l100h�?�?0�?00时滞可燃物载量，下同。TN, total nitrogen; NH₄+-N, ammonium nitrogen; NO₃∑�/sup>-N, nitrate nitrogen; AN, alkali-hydrolysable nitrogen; TH, tree height; Ccover, canopy coverage; Slope, slope gradient; Position, slope position; m1h, m10h, m100h: the fuel moisture content of 1, 10 and 100 h; l1h, l10h, l100h: the fuel loads of 1, 10, 100 h. The same below.}

Figure 2.Correlation matrix of soil nitrogen element with stand factor, site factor and fuel factor

下载: 全尺寸图牆�/a> 幻灯牆�/a>

�?nbsp; 3土壤氮冗余分枏�/p>

Figure 3.Soil nitrogen redundancy analysis

下载: 全尺寸图牆�/a> 幻灯牆�/a>

�?nbsp; 1样地基础信息

Table 1.Basic information of sample plots

火强�?br/>Fire intensity	样地序号 Sample plot No.	地理坐标 Geographical coordinate	平均树高 Mean tree height/m	胸径 DBH/cm	郁闭�?br/>Canopy coverage	平均熏黑高度 Mean blackened height/m	树木死亡玆�br/>Tree mortality/%
对照 Control（CK（�/td>	1	118°28�?5″E�?1°20�?6″N	7.20	12.00	0.85	0.00	0.00
	2	118°28�?8″E�?1°20�?8″N	5.30	8.70	0.80	0.00	0.00
	3	118°28�?9″E�?1°20�?8″N	6.40	8.80	0.82	0.00	0.00
轻度 Light（L（�/td>	1	118°28�?3″E�?1°20�?6″N	5.30	12.00	0.75	0.42	13.26
	2	118°28�?3″E�?1°20�?7″N	5.00	8.20	0.72	0.50	18.20
	3	118°28�?3″E�?1°20�?7″N	7.40	13.20	0.70	0.67	16.35
中度 Medium（M（�/td>	1	118°28�?7″E�?1°20�?8″N	15.80	17.20	0.69	4.70	54.60
	2	118°28�?8″E�?1°20�?5″N	7.10	8.60	0.71	3.70	63.46
	3	118°28�?7″E�?1°20�?7″N	8.60	12.60	0.70	3.95	66.72
重度 High（H（�/td>	1	118°28�?9″E�?1°20�?6″N	8.50	16.30	0.00	8.50	100.00
	2	118°28�?9″E�?1°20�?6″N	9.20	11.90	0.00	9.20	100.00
	3	118°28�?9″E�?1°20�?5″N	11.40	12.80	0.00	11.40	100.00

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�?nbsp; 2方差分析结果

Table 2.Analysis of variance results

指标 Index	全氮 TN				铵态氮 NH4+-N				硝态氮 NO3∑�/sup>-N				碱解� AN
	2015	2016	2021		2015	2016	2021		2015	2016	2021		2015	2016	2021
火强� Fire intensity (I)	0.000*	0.006*	0.202		0.000*	0.108	0.070		0.003*	0.000*	0.053		0.000*	0.197	0.066
土层深度 Soil layer depth (La)	0.000*	0.003*	0.013*		0.000*	0.012*	0.252		0.005*	0.004*	0.284		0.000*	0.405	0.009*
I× La	0.000*	0.629	0.980		0.000*	1.000	0.870		0.022*	0.034*	0.573		0.000*	0.513	0.934
年份 Year (Y)		0.000*				0.000*				0.167				0.000*
I×Y		0.007*				0.001*				0.000*				0.004*
La ×Y		0.209				0.000*				0.055				0.003*
I× La ×Y		0.787				0.957				0.119				0.962
注：*表示显著影响＋�i>P< 0.05，加粗字体表示双因素/三因素方差分析结果显著。Notes: * means significant impact,P< 0.05. Bold font indicates significant results of two-factor/three-factor ANOVA.

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