Plant carbon pools and fluxes in coppice regrowth of Eucalyptus globulus

Forestry systems frequently utilise coppice regrowth to establish 2nd and later rotations, partly because early growth in coppice is often faster than in seedlings. This rapid regrowth is to some extent attributable to translocation of below-ground reserves to support the development of new shoots. Translocation of below-ground carbon (C) from either the existing soluble pool or C mobilised from storage could require elevated respiration rates in roots. We studied changes in the rate of CO2 efflux (R15) and total soluble sugar (TSS) concentration from different components of coppice and uncut trees in a Eucalyptus globulus (Labill.) plantation for 8 months after cutting. We also examined the impact of shading of the regrowth coppice as a means of increasing the dependence on carbohydrate reserves. The R15 of lateral roots declined soon after trees were felled but increased in uncut (control) trees. The TSS concentration decreased in the lateral roots of coppiced trees and also in the lateral roots of uncut trees. Early coppice regrowth was not associated with an elevated R15 or alteration to the TSS concentration of roots. A mass balance of C derived 8 months after trees were felled suggested that coppice maintained a significant amount of soluble C in roots, even though net C fixation was low, especially in the shaded treatment. One explanation for these observations is that mobilisation and/or transport of C in developing coppice is sink-limited, or alternatively, translocation of C from roots to shoots is constrained by vascular connections.