长白山垂直带森林叶片-凋落物-土壤连续体有机碳动态——基于稳定性碳同位素分析

Organic carbon dynamics of the leaf-litter-soil continuum in the typical forests of the Changbai Mountain transect: an analysis of stable carbon isotope technology

稳定性碳同位素自然丰度(δ^(13)C)记录着生态系统碳循环过程的关键信息,常被用于评价全球变化情景下陆地生态系统碳的动态。以长白山北坡垂直带4种典型森林生态系统为研究对象,测定乔木建群种叶片、凋落物以及不同深度土壤有机碳(SOC)含量和δ^(13)C值,探讨植物叶片-凋落物-土壤连续体碳含量、δ^(13)C丰度的分布格局及其生态学暗示。研究结果表明:植物叶片碳含量随海拔高度的增加呈现抛物线型变化,且阔叶树叶片碳含量显著低于针叶树,体现气候要素和植被功能型的支配作用,并且暗示针叶树种潜在的碳蓄积能力更强。此外,植物叶片δ^(13)C随海拔高度升高而降低,表明高海拔植物叶片水分利用效率较低,即固碳耗水成本更高。凋落物碳含量随海拔增加逐渐下降,而矿质表层土壤则表现为阔叶红松林、岳桦林显著高于暗针叶林,体现了植被类型和土壤质地的共同支配作用。总体上,岳桦林SOC周转最快,其次是暗针叶林,位于基带的阔叶红松林最慢。可见,小尺度上气候因子并不是温带森林地下碳循环的主导因素,植被功能型和土壤属性对SOC周转与稳定的影响更大。在探讨环境因子对陆地生态系统碳循环和碳平衡的影响时需要考虑研究尺度,不同的研究尺度影响SOC周转的驱动因子并不相同。研究方法方面,基于log SOC和δ^(13)C的SOM周转模型能够很好地概括不同生态系统类型下SOM周转的相对快慢,可用来评价SOC动态对全球变化的响应。

The natural abundance of the stable carbon isotope （δ 13C） records key information regarding the ecosystem carbon （C） cycle and is commonly used to assess the C dynamics in terrestrial ecosystems under global change. In this study, we selected four typical forest ecosystems along the vertical transect distributed in Changbai Mountain and measured the C concentrations and δ 13C values of leaves of constructive tree species, litter, and soils at different soil layers. The aim of this study was to explore the patterns of C content and δ 13C values in the leaf-litter-soil continuum, as well as their ecological indications. The results showed that foliar C content first increased and then decreased with the increasing altitude, and the parabolic peak appeared at the Ermans birch-spruce-fir forest stand; moreover, the C content of broadleaved tree species was significantly lower than that of coniferous species, reflecting that coniferous species had a higher C sequestration capacity relative to that of broadleaved species. Climatic factors and vegetation types dominated the pattern of foliar C content. In addition, foliar δ 13C decreased with increasing altitude, indicating that vegetation at high-altitude sites had lower water use efficiency （WUE） and higher water consumption by C sequestration relative to that at low altitude sites. Litter C content gradually decreased with increase in altitude, whereas topsoil C content at the 0-20 cm depth at the broad-leaved Korean pine forest （BLKP） and Ermans birch forest （EB） was higher than that of the Korean pine-spruce-fir forest （KPSF） and Ermans birch-spruce-fir forest （EBSF）, reflecting the predominance of vegetation type and soil texture together. Overall, the birch forest had the highest SOC turnover rate, followed by that of the two dark coniferous forests, and that of the broad-leaved Korean pine forest was the lowest. Our results suggest that climatic factors are not the predominant factors in the belowground C cycle of temperate forests at a small scale, and vegetation functional types and soil properties could have greater effects on the turnover and stability of SOC. Because the factors driving the turnover of SOC are not the same at different study scales, we should more intensively consider the research scale when we explore the effects of environmental factors on C cycle and C budget in terrestrial ecosystems. The SOM turnover model, based on the regression of logSOC and δ 13C, is a good method to characterize the rate of SOM turnover in various ecosystems, which can be used to evaluate the response of SOC dynamics to global change.