QUANTITATIVE CARBON DISTRIBUTION IN CLONAL PLANTS OF WHITE CLOVER (TRIFOLIUM-REPENS) - SOURCE SINK RELATIONSHIPS DURING UNDISTURBED GROWTH

The assimilation and distribution of carbon in laterally spreading white clover plants was quantified in a controlled environment using CO2 exchange rate measurements and C-14 as a tracer. Plants were restricted to three mature leaves on the main stolon apex, and the movement of C-14 from these leaves (and one immature, but carbon-exporting, leaf) to meristematic zones throughout the plant was determined by detailed plant dissection. Sinks throughout the plant drew small to moderate proportions (typically 1-8%) of the C-14 exported by all mature leaves. The three mature leaves displayed similar export patterns, and no specific source-sink relationships involving any of these leaves were observed. However, C-14 exported by the developing leaf moved predominantly to the main stolon apex, and to adjacent young stolon tissue. Estimated respiratory losses over 24 h accounted for 40-49% of the C-14 fixed. Of the total amount of C exported by all four leaves and utilized in new growth or reserve storage, 22% moved to the main stolon apex, 16% to stolon tissue of the main stolon, 34% to adventitious roots on the main stolon (most of which was utilized in older, nodulated roots) and 29% to branches. The apex received the greatest amount of C/unit weight, reflecting its high sink activity, its proximity to the source leaves and, possibly, apical dominance. Subtending leaves provided 46-51% of the C utilized by young branches. Older branches continued to import significant quantities of C from parent stolon leaves despite having their own C sources, though parental support for branches was seen to decrease as branches aged, when the quantity of C they imported was expressed as a function of their weight. Relative sink strength and distance between sources and sinks contributed to the observed patterns of C distribution. No apparent restriction on C movement was imposed by the vascular architecture of stolons.