An assessment of carbon and nutrient limitations in the formation of the southern Andes treeline

Although the principal mechanism determining tree line formation appears to be carbon (C)-sink limitations due to low temperatures, few studies have assessed the complementary role of reduced soil nutrient availability with elevation. We tested the hypothesis that nutrient (especially nitrogen, N) limitations at tree line may directly (via C-source) or indirectly (via C-sink) reduce the growth of a winter deciduous tree line species.
If a shortage of soil N with elevation is involved in tree line formation, it should occur in two alternative ways: (i) through sink limitations because N is required for tissue formation, which would indirectly limit C investments (N decreases and C reserves increase with elevation), and (ii) through C limitations because this would lead directly to a reduction of photoassimilates (N and C reserves decrease with elevation).
In testing our hypothesis, we analysed tree growth rates (basal area increment), twig non-structural carbohydrate (NSC) and N concen...