Are carbohydrate storage strategies of trees traceable by early-latewood carbon isotope differences?

Key message : Investigations of stable isotopes in early- and latewood cellulose offer interesting insights to climate-driven adaptations of trees' carbon storage strategy during different phenological phases. Abstract: We investigated δ13C isotopic composition in both earlywood and latewood. The origin of the samples is an oak forest (Quercus petraea), situated in Switzerland. A comparison of isotope compositions between early- and latewood can help us to investigate and understand the processes of plant metabolism in more detail. The fact which we found excellent correlations (r 2=55%) between early- and latewood for carbon isotopes strengthens the common knowledge that atmospheric CO2 acts as the major carbon source for latewood but the earlywood strongly depends on the reserves from previous years (r 2=68%), at least for oaks investigated in this study. In addition, that no correlation between late woods (r 2=0-5%) was found, manifests the higher variability of direct assimilates. Furthermore, we examined the impacts of increasing air temperature and CO2 concentration on carbohydrate fluxes in trees and we found remarkable differences between two time periods. In the period ad 1780-1825, the trees intensely used the young reserves while in the period ad 1960-1994, there is no clear preference of them. This suggests that in the latter period, a larger volume of reserves is available and that the new assimilated reserves (previous year) do not play the most important part, mainly due to the very favourable conditions induced by climate change, at the investigated site. In conclusion, a carbon isotope approach on early- and latewood samples is ideal to investigate isotope incorporation pathways of physiological processes. This will augment the interpretation of tree ring isotope records with respect to the assignments of their variations to specific biochemical processes within the tree, i.e. carbon allocation