林火干扰是驱动北方森林生态系统更新、演替以及物质循环的重要生态过程。林火的发生,显著地改变了北方森林地表以及土壤表层生物量和碳密度。然而,我们对林火是否对北方森林深层土壤(40cm以下)这个储量巨大的碳库的影响却缺乏关注。以大兴安岭呼中林区2010年火烧迹地为研究对象,并以相邻同等立地条件的未过火区为对照,通过样地调查、实验室分析,对林火对北方森林深层土壤碳密度的影响以及其与驱动因子的关系做了分析。结果显示:火烧迹地土壤有机碳随深度的分布规律与未火烧对照样地有显著差异,其深层土壤有机碳含量与碳密度显著低于未火烧区(n=56,P<0.001);火烧迹地深层土壤有机碳中微生物量碳含量、易氧化有机碳含量显著高于未火烧迹地(n=56,P<0.01),而土壤碳氮比、可溶性有机碳含量显著低于未火烧样地(n=56,P<0.01);火烧迹地深层土壤含水量显著低于未火烧样地(n=56,P<0.001),而土壤温度和pH值则显著高于未火烧迹地(n=56,P<0.001)。由此可见,林火显著地降低了北方森林深层土壤有机碳的化学稳定性,并使土壤温度增加,促进了土壤微生物的生长,最终导致了深层土壤有机碳分解加速,储量下降。

Forest fire is one of the most important ecological process that drives the regeneration,succession and material circulation of boreal forests.The aboveground and surface soil biomass and carbon density of boreal forests were significantly changed by forest fire.Subsoil carbon pool,which may store almost half of soil carbon of boreal forest,is also strongly influenced by forest fire,however,was paid little attention to.In this study,we measured effect of fire on subsoil carbon density,and analyzed relationship between subsoil carbon density and its driving factors in a 2010 burned site at Huzhong Natural Reserve in Great Xing’an Mountains.Results showed that the distribution of soil organic carbon(SOC)content along depth in burned sites were significantly different from that of unburned control sites,deep SOC content and carbon density in burned sites were significantly lower than that in the control sites(n=56,P<0.001);microbial biomass carbon content and easily oxidized organic carbon content in burned sites were significantly higher than that in control sites(n=56,P<0.01),but soil C/N and dissolved organic carbon content were significantly lower than that in control sites(n=56,P<0.01).Soil moisture in burned sites was significantly lower than the control(n=56,P<0.001),but soil temperature and pH were significantly higher than those in control sites(n=56,P<0.001).Our results suggested that forest fire significantly reduced chemical stability of subsoil SOC of boreal forests,promoted the growth of soil microorganism by increasing soil temperature,and eventually led to the accelerated decomposition of SOC and the decrease of subsoil SOC storage.