中度强度森林火灾对马尾松次生林土壤有机碳密度的影响

森林火灾作为森林非连续的干扰因子, 是生物地球化学循环的驱动因子, 显著改变生态系统的结构和功能及养分循环与能量传递, 引起森林碳库与碳分配格局的变化, 进而影响森林演替进程及固碳能力。该研究以广东省马尾松(Pinus massoniana)次生林为研究对象, 采用相邻样地比较法和空间代替时间法, 以野外调查采样与室内试验分析为主要手段, 定量研究突发性森林火灾对土壤有机碳密度的影响, 探讨森林火灾对土壤有机碳固持的影响机制。结果表明: 与对照相比, 森林火灾后的幼龄林、中龄林和成熟林的土壤有机碳密度分别为35.12、40.80和52.34 t·hm^-2, 依次降低了10.93%、8.52%和7.56%。相比对照, 幼龄林、中龄林和成熟林土壤剖面(0-60 cm)的土壤有机碳密度变化范围分别为5.04-7.76、5.26-10.27和6.33-13.58 t·hm^-2, 依次降低了2.51%-16.83%、1.31%-11.85%和1.09%-12.50%; 森林火灾显著降低了幼龄林和中龄林0-30 cm的土壤有机碳密度, 显著降低了成熟林0-20 cm的土壤有机碳密度。马尾松次生林土壤有机碳密度与土壤理化性质具有显著相关关系。通径分析表明, 对照样地和过火样地中, 土壤全氮含量均对土壤有机碳密度的直接作用最大, 土壤细根生物量对土壤有机碳密度的直接作用较小, 但其通过土壤全氮含量对土壤有机碳密度的影响均表现在间接作用上。嵌套方差分析表明, 土壤深度解释了土壤有机碳密度变异的70.60%, 林龄解释了其变异的25.35%, 森林火灾解释了其变异的2.34%。研究发现: 森林火灾减少了马尾松次生林各林龄的土壤有机碳密度。在水平方向上, 随着林龄增长, 土壤有机碳密度的减少幅度降低; 在垂直方向上, 土壤有机碳密度随着土壤土层深度加深而降低, 且随林龄增长减少幅度下降。研究森林火灾对森林生态系统土壤有机碳的影响, 有助于理解森林生态系统土壤碳固持和碳循环过程, 对制定旨在减缓全球变化的科学合理的林火管理策略具有重要意义。

Effects of moderate forest fires on soil organic carbon density in secondary forests of Pinus massoniana

Aims As a discontinuous disturbance factor, forest fire is one of the drivers of biogeochemical cycles. It significantly changes the structure and function, nutrient cycling, and energy transfer of ecosystems and alters the forest carbon pools and carbon distribution patterns, consequently affecting the processes of forest succession and carbon sequestration capacity. This study aims to determine the impacts of incidental forest fire on soil organic carbon density, and to explore the mechanisms of forest fire impacts on soil organic carbon fixation. Methods The study was conducted in secondary Pinus massoniana forests of different ages in Guangdong Province, using the method of space for time substitution. The sampling plots were set up on adjacent sites of burned and control stands, and soil samples (0-60 cm) were collected from each plot for indoor tests and analysis of the physical and chemical properties. The soil organic carbon components were measured and calculated for density. Changes in soil physical and chemical properties and soil organic carbon with forest ages were quantified. Important findings Fire reduced the soil organic carbon density in secondary P. massoniana forests; the level of reduction in soil organic carbon density decreased with forest age and soil depth. Compared with the controls, the soil organic carbon density in the burned plots of young, mid-age and mature forests were 10.93%, 8.52% and 7.56% lower, respectively. The soil organic carbon density in the burned plots of young, mid-age and mature forests varied in the range of 5.04-7.76, 5.26-10.27 and 6.33-13.58 t·hm^-2, respectively, along the soil profile of 0-60 cm, which were 2.51%-16.83%, 1.31%-11.85% and 1.09%-12.50% lower, respectively, than the controls. Fire significantly reduced the soil organic carbon density of the young and the mid-age forests in the 0-30 cm soil layer, and of the mature forest in the 0-20 cm soil layer. There were significant correlations between soil organic carbon density and soil physical and chemical properties. Path analysis revealed the greatest direct effect of soil total nitrogen content on soil organic carbon density in both the control and burned plots; fine root biomass had a smaller direct effect, but imposed an indirect effect on soil organic carbon density via its controls on soil total nitrogen content. Nested ANOVA showed that soil depth accounted for 70.60% of the variations in soil organic carbon density, forest age 25.35%, and fire 2.34%.