Carbon allocation changes: an adaptive response to variations in atmospheric CO2

Abstract:

Given the ubiquity of nutrient constraints on primary production, an optimal carbon allocation strategy is expected to increase total below-ground allocation (fine root production and turnover, allocation to mycorrhizae and carbon exudation to the rhizophere) as CO₂ concentration increases. Conversely, below-ground allocation should be reduced under low CO₂ concentrations, as occurred during glacial times. Using a coupled generic primary production and tree-growth model, we quantify the changes in carbon allocation that are required to explain the apparent homoeostasis of tree radial growth during recent decades and between glacial and interglacial conditions. These results suggest a resolution of the apparent paradox of continuing terrestrial CO₂ uptake (a consequence of CO₂ fertilization) and the widespread lack of observed radial growth enhancement in trees. Adaptive shifts in carbon allocation are thus a key feature that needs to be accounted for in models to predict, for example, future timber yields as well as in large-scale ecosystem and carbon cycle models.