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
The natural abundance of the stable carbon isotope (delta~(13)C) 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 delta~(13)C 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 delta~(13)C 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 delta~(13)C 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 020 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 delta~(13)C, 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.