The carbon isotope composition of the CO2 efflux (delta C-13(E)) from ecosystem components is widely used to investigate carbon cycles and budgets at different ecosystem scales. delta C-13(E,) was considered constant but is now known to vary along seasons. The seasonal variations have rarely been compared among different ecosystem components.
We aimed to characterise simultaneously the seasonal dynamics of delta C-13(E) in different compartments of two temperate broadleaved forest ecosystems.
Using manual chambers and isotope ratio mass spectrometry, we recorded simultaneously delta C-13(E) and delta C-13 of organic matter in sun leaves, current-year twigs, trunk bases and soil in an oak and a beech forest during 1 year.
In the two forests, delta C-13(E) displayed a larger variability in the tree components than in the soil. During the leafy period, a pronounced vertical zonation of delta C-13(E) was observed between the top (sun leaves and twigs with higher values) and bottom (trunk and soil with lower values) of the ecosystem. No correlation was found between delta C-13(E) and delta C-13 of organic matter. Causes for these seasonal variations and the vertical zonation in isotope signature are discussed.
Our study shows clear differences in values as well as seasonal dynamics of delta C-13(E) among different components in the two ecosystems. The temporal and local variation of delta C-13(E) cannot be inferred from organic matter signature or CO2 emission rates.