Mechanisms and Controls of Carbon Flux: Carbon Fixation and Allocation

Abstract

It is a fair presumption that nearly all major plant types in most of the worldߣs biomes have been enclosed in chambers or porometers at one time or another to test their gas exchange characteristics (KÖrner, 1994). Thus it might seem superfluous to write yet another chapter dealing with carbon assimilation and allocation (see Schulze and Caldwell, 1994). However, despite this long history of carbon assimilation research, we are still unable to quantify the actual and the potential carbon fixation of the terrestrial surfaces of the globe (Tans, 1993). We are also still far from a mechanistic understanding of resource allocation and utilization in plants (see Schulze, 1994). The reason for this lack of mechanistic understanding and predictive power are manifold. In contrast to former views, we now realize that (1) the basic assumption of a carbon limitation of plant growth is not appropriate for most field conditions, (2) that maximization of productivity may very often be fatal, and (3) that there are intrinsic fast and slow growing species, which occupy the land surface by competition and through traits which are only partially related to productivity. Plant geography, biodiversity, plant form, and canopy processes are additional factors to be considered when dealing with carbon economy at a global scale.