大兴安岭北部试验林火影响下土壤有机碳含量的时空变化

Temporal and Spacial Changes of Total Soil Organic Carbon Content as Affected by an Experimental Forest Fire in the Greater Xing'an Mountains

在大兴安岭北部寒温带针叶林地进行严密监控下的秋季野外林火点烧试验。通过样地网格布点和火烧前后对比监测,研究林火影响下土壤(0-10cm)有机碳含量的时空动态。结果显示,林火过后土壤有机碳含量变化的方向和程度因火烧强度和时间阶段而异,各阶段变化的空间格局与林火强度格局相一致。轻、中度火烧对土壤有机碳的即时影响不显著;经过第2年融雪季和雨季后,土壤有机碳含量有显著的小幅递增,平均增幅3.5%～4.2%;至火烧后第3年秋季显著回降。重度火烧后土壤有机碳含量有极显著的即时下降,平均降幅14.6%;经过第2年融雪季和雨季后,变化呈两极分化,大部分点位持续大幅度降低(平均降幅25.4%),个别点位大幅度增高(增幅78.7%);至火烧后第3年秋季,两极分化进一步加剧,降低点位有机碳含量平均降幅39.9%,个别增高点位有机碳含量增幅却高达107.2%。轻、中度火烧土壤有机碳增高的主导因素是植被和枯落物层有机颗粒物、炭化颗粒物以及半腐烂死细根混入等;而其后期回落则主要与表土层塌缩有关。重度火烧土壤有机碳降低的主导因素是表层有机碳燃烧损失和高温挥发损失,以及后期的侵蚀损失等;其后期局部区域大幅增高,主要是洼地有机碳堆积所致。另外,表土塌缩、烧毁、侵蚀均导致采样深度下延,下层土壤对含量指标的"稀释效应"是土壤有机碳含量变化的重要叠加因素。

An experimental wild fire was conducted in the boreal forest of Greater Xing＇an Mountains,in late autumn,2009.This study examined the temporal and spacial variations of total soil organic C（SOC） content after the fire,by latticed co-coupled sampling（0-10 cm） method,in a time sequence of 0~3 years.The direction and significance of SOC changes were found to be variable,largely depend upon the intensity of the fire and the period after the fire,and the special patterns of SOC changes in each period were consistent with the pattern of forest fire intensity.Low and moderate forest fire led no significant change in SOC immediately after burning;in autumn of the second year,when the leaching seasons（spring snow-melting and summer rain） passed,SOC increased by 3.5%～4.2% in average for these two fire intensity treatments,which was statistically significant according to＇paired-samples t test＇;but in autumn of the third year,this small amplitude of increase had turned to decrease by 2.6%～4.9%.There existed very significant immediate decrease（14.6% in average） of SOC when suffered high-intensity fire;when the burned soil endured through leaching seasons（spring snow-melting and summer rain） of the second year,SOC changes were characterized by a tendency towards polarization,of which most parts decreased continuously（25.4% in average）,whereas some exceptional position of the sites increased dramatically（78.7%）;in autumn of the third year,the polarization was aggravated,with an average decrease of 39.9% in the majority of decreasing areas,and an increase of 107.2% at some exceptional position.The dominant factors leading to post-fire SOC changes under different fire intensities were discussed,including incorporation of forest necromass and charcoal substances,combustion and volatilization losses of humic top soil under high-intense fire,accelerated soil OM mineralization and soluble OM leaching losses,soil erosion and deposition,shrink-co-sinking of top soils,and the ＇dilution effects＇ of deeper soils caused by shift-down in sampling depth（0-10 cm protocol） as well.