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Quantitative carbon distribution in clonal plants of white clover (Trifolium repens): source-sink relationships during undisturbed growth

SUMMARY The assimilation and distribution of carbon in laterally spreading white clover plants was quantified in a controlled environment using CO2 exchange rate measurements and 14C as a tracer. Plants were restricted to three mature leaves on the main stolon apex, and the movement of 14C 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 14C 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, 14C 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 14C 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.