大兴安岭北端地形因子对针叶林土壤黑碳储量的影响

【目的】气候变化对人类社会发展产生的影响受到了世界各国的广泛关注,提高森林生态系统的固碳潜力被认为是经济可行且有效减缓大气二氧化碳(CO₂)浓度的重要途径之一,大兴安岭地区森林生态系统的黑碳储量在全球碳循环和碳汇方面具有重要的作用。研究大兴安岭不同地形因子条件下土壤黑碳的储藏分布特征,为区域森林土壤黑碳储量准确估算和森林土壤固碳功能的定量评估提供参考依据。【方法】在大兴安岭北端寒温带针叶林区,按照坡位、坡向差异,对称设置20块样地,采集1 m剖面内不同发生层土样。采用氢氟酸(HF)和盐酸(HCl)处理的重铬酸盐氧化方法对土壤黑碳进行分离,探讨了地形因子(坡位、坡向和坡度)对黑碳(BC)分布的影响,并借助逐步回归分析量化各因子对土壤黑碳密度变异的相对影响程度。【结果】①研究区土壤黑碳密度(面密度)范围为0.02~3.64 kg/m²,腐殖质层密度最大,占全剖面的50.3%,具有明显的表层集聚效应;黑碳占有机碳的比例范围为3.7%~42.5%,除凋落物层外随深度增加呈不断增加的趋势,说明黑碳含量依土层减小的程度比有机碳含量依土层减少的程度小,对比非黑碳成分黑碳向下迁移的程度更大,其稳定性更强;各土层黑碳含量变化范围为0.24~59.13 g/kg,空间变异性较大。②坡位显著影响土壤黑碳含量和密度的分布,不同土层之间下坡位的黑碳含量均显示高于上坡位,下坡腐殖质层黑碳密度是上坡的2.21倍,其1 m剖面黑碳密度是上坡的1.91倍;不同土层间黑碳占有机碳比例均显示下坡位高于上坡位,而差异未达到显著水平;逐步回归显示,坡位对土壤黑碳数量分异的影响较大,可独立解释腐殖质层黑碳密度空间变异的42.1%、1 m剖面黑碳密度空间变异的46.0%。③坡向通过光照和温度的不同影响黑碳储量分布,总体看来,BC含量(除凋落物层和母质层)和BC密度(除凋落物层)均显示阳坡略高于阴坡,但差异不显著,故坡向对黑碳影响较小;腐殖质层土壤BC密度与坡度无显著相关性,而按上下坡分组统计比较淀积层和全部1 m剖面,则上下坡点位分群趋势明显,下坡BC密度与坡度呈显著正相关,上坡BC密度与坡度无显著相关性,坡度对黑碳分布的影响不及坡位大。【结论】大兴安岭林区黑碳储量丰富,BC主要存在于土壤表层并缓慢向下迁移,其生物化学惰性可有效促进碳固定,提升森林土壤碳汇能力。坡位是影响研究区域森林土壤黑碳分布的主控因子,在同一发生层内,不同坡位的土壤剖面间由于土壤理化性质、植被类型、地表径流冲刷作用等因素的各异导致黑碳含量和密度存在较大差异。研究结果可部分解释区域黑碳分布规律,并为碳汇林立地的选取与经营提供参考。

Effects of topographic factors on soil black carbon storage in coniferous forests at the north end of Greater Khingan Mountains

【Objective】The impact of climate change on the development of human society has attracted extensive attention all over the world.Improving the carbon sequestration potential of forest ecosystems is considered to be one of the important ways to reduce atmospheric CO2 concentration economically and effectively.The black carbon(BC)reserves of forest ecosystems in the Greater Khingan Mountains area play an important role in the global carbon cycle and carbon sequestration.The storage and distribution characteristics of soil BC under different topographical factors were studied in order to provide basic parameters for the accurate estimation of BC storage in regional forest soil and for the quantitative evaluation of forest soil carbon sequestration.【Method】Based on differences in slope positions and slope aspects,20 sample plots were set up symmetrically in the cold temperate conifer forest area at the northern end of the Greater Khingan Mountains,and soil samples from different occurrence layers in 1 m sections were collected.Soil BC was separated by the oxidation of dichromate treated with HF/HCl.The effects of topographical factors(the position,aspect and gradient of slope)on the distribution of soil BC were investigated.The relative influence of each factor on the variation in soil BC density was quantified by the stepwise regression analysis.【Result】①The soil BC density in this area ranges from 0.02 to 3.64 kg/m2.The density of the humus layer was the highest,accounting for 50.3%of the total,which had an obvious surface agglomeration effect.The BC contributions ranged from 3.7%to 42.5%of the organic carbon.With increasing depth,there was an increasing trend(except for the litter layer).The results showed that the degree of decrease of the BC content in the soil layer was smaller than that of the organic carbon content,according to the soil layer.Compared with the non-BC composition,the downward migration of BC was greater,and its stability was stronger.The variation range of the BC content in each soil layer was 0.24 to 59.13 g/kg,and the spatial variability was large.②The soil BC content and density distribution were significantly affected by the slope position,and the BC content in the downslope position between different soil layers was higher than that in the upslope position.The density of BC in the humus layer of the downslope position was 2.21 times higher than that in the upslope position,and the BC density of the 1 m profile in the downslope position was 1.91 times than that of the upslope position.The ratio of BC to the organic carbon in different soil layers showed that the downslope ratio was higher than the upslope,but the difference did not reach a significant level.The stepwise regression showed that the slopes position had a great effect on the differentiation of soil BC.Slope could independently explain 42.1%of the spatial variation of BC density in the humus layer and 46.0%of the spatial variation of BC density in the 1 m profile.③The slope aspect affects the distribution of BC reserves through different illumination and temperatures.Overall,the BC content(except for the litter layer and the parent material layer)and BC density(except for the litter layer)showed that the sunny slope was slightly higher than the shady slope,but the difference was not significant.Thus,the slope aspect had little effect on BC.There was no significant correlation between the soil BC density and slope in the humus layer,compared with the 1 m profile and the illuvial horizon according to the upslope and downslope grouping.The trend of the point grouping was obvious:the BC density in the downslope was positively correlated with the slope,the BC density in the upslope was not significantly correlated with the slope,and the influence of the slope on BC distribution was not as great as that of the slope position.【Conclusion】The Greater Khingan Mountains forest region is rich in BC reserves.The black carbon mainly exists in the surface layer of soil and moves slowly.Its biochemical inertia can effectively promote carbon fixation and enhance the carbon sequestration capacity of forest soil.The slope position is the main control factor affecting the distribution of BC in forest soil in this region.In the same layer,there are great differences in the BC content and density among different soil profiles owing to different soil physical and chemical properties,vegetation types,surface runoff scour,and so on.The research results can partly explain the distribution of BC in the region and provide a reference for the selection and management of carbon sequestration forest sites.