THE CARBON ECONOMY OF CLONAL PLANTS OF TRIFOLIUM-REPENS L

Fluxes of carbon between sources and sinks were quantified for clonal plants of Trifolium repens L. (cv. Blanca) in two glasshouse experiments. Carbon sources were (a) leaves on the parent (= main) stolon apex, or (b) leaves on either young or old branches. and the major sinks of interest were the parent stolon apex, branches, and the adventitious root arising at the same parent stolon node as a young source branch. Defoliation treatments were applied to the parent stolon and/or branches (excluding source branches). Carbon moved freely from the parent stolon to branches and vice-versa: these bidirectional exchanges of C provided important supplementary sources of carbohydrate for the sinks and buffered them against the effects of defoliation. Young branches exported more C to the parent plant (mean = 6.3-mu-mol d-1) than they imported from leaves on the parent stolon (5.2-mu-mol d-1) which, in turn, exceeded the amount fixed by leaves on the branch and utilized within the branch itself (2.7-mu-mol d-1). In contrast, the C economy of old branches was largely self-contained with, on average. 25.4-mu-mol C d-1 exported to the parent plant, 1.8-mu-mol d-1 imported from the parent, and 63.0-mu-mol d-1 fixed and utilized by the branch itself. Thus the growth of young branches was immediately reduced by removal of parent stolon leaves, but old branches were unaffected. An estimated 42% of the C utilized by the main stolon apex originated from branches, while by far the largest proportion (84%) of the C used for growth of young nodal roots originated from the associated branch and not from leaves on the parent stolon to which the root was directly attached.