Dynamics of carbon and nitrogen accumulation and C:N stoichiometry in a deciduous broadleaf forest of deglaciated terrain in the eastern Tibetan Plateau

Abstract

Although many studies have focused on the spatial distribution of global carbon (C), there are still considerable uncertainties associated with the global C budget due to insufficient and incomplete data. The sequestration of ecosystem C corresponding to different ages provides a more accurate method for quantifying the C budget. In this work, the chronosequence approach was used to explore the relationship between the C dynamics and the carbon:nitrogen (C:N) stoichiometry in a broadleaf forest of a deglaciated terrain. The database included five successional sites, and each site consisted of three parallel plots. Our results showed that (1) C and N can accumulate in aboveground vegetation, forest floor, and mineral soil throughout the terrain ages, (2) the relative contribution to the total ecosystem C increased in aboveground vegetation and decreased in mineral soil with increasing terrain age, (3) C and N scaled isometrically (the slope of relationship between the rates of relative C and N changes is significant from 1.0) along the successional sequence in the aboveground vegetation but not in mineral soil, and (4) the C:N ratio kept constant in the aboveground vegetation and decreased in mineral soil, which implies a more rapid N accumulation in mineral soil. These results demonstrate that the increased C storage was accompanied by N accumulation in all of the layers throughout the terrain age and that the aboveground vegetation became a primary ecosystem C pool. However, it should be considered that the carbon has been flowing into the soil from belowground.