Christian Körner's evaluation

"This paper contributes significantly to answering a long standing question, namely whether trees grow slower as they get bigger and older because they fall increasingly short in photoassimilates (carbon). The authors show that for southern beech (Nothofagus) in Chile, there is no decline in tissue carbon charging with non-structural carbohydrates as trees age or get taller. Thus, growth retardation is not related to carbohydrate starvation.

When plants reduce their growth in response to all sorts of internal and external constraints, we are commonly inclined to attribute this to a shortage in photoassimilates. There is increasing evidence that this is a vision of the plant world that is largely driven by our ability to measure photosynthesis (hence giving carbon provision a priority), with no appropriate methodical access to constraints operating directly at the tissue level {1}. In the meantime, it is well established that low temperatures or drought operate primarily at the tissue level, causing photoassimilates to actually overshoot, because leaf metabolism is less constrained than tissue formation (see ref {2}, on which I am the author). This paper adds another piece of evidence for tree aging as well as drought. The study parallels an earlier study of pines by Sala et al. {3}. This paper by Piper and Fajardo clearly falsifies the hypothesis that age or drought related growth reductions are related to carbon shortage. Such findings have substantial implications for modelling and the underlying ecological theory, which still prioritizes carbon capture as the overarching control of plant growth. We need more works taking this direction."

{1} Muller et al. J Exp Bot 2011, 62:1715-29 [PMID:21239376].
{2} Körner C, J Ecol 2003, 91:4-17 DOI:10.1046/j.1365-2745.2003.00742.x (accessed Oct 17 2011).
{3} Sala et al. New Phytol 2010,186:274-81[PMID:20409184].