Carbohydrate dynamics in roots and rhizomes of Cirsium arvense and Tussilago farfara

Information on the source-sink dynamics of carbohydrates during early plant growth can indicate when perennial weeds are most vulnerable to mechanical control. In this study, carbohydrate contents in the roots or rhizomes of two noxious perennial weeds, Cirsium arvense and Tussilago farfara, and basipetal translocation of photo-assimilates were measured. We used HPLC for carbohydrate measurements and (14)C labelling to follow the translocation of photo-assimilates during early growth. These measurements were related to leaf number and leaf area. Fructan and fructose changed significantly over the experimental periods. Fructan for both species was greatest within 2 weeks after planting 5-cm-long root/rhizome fragments and declined there-after. After 2 weeks, fructose concentrations, which were at their minimum level at planting time, rose sharply because of fructan depolymerisation. The radioactive carbon applied to the aerial parts translocated rapidly to root or rhizome systems around 500-600 d degrees C after emergence. We concluded that while the fructan was continuously depleted in the roots or rhizomes and reached their minimum levels 33 days after emergence (DAE), the basipetal translocation of photo-assimilates started earlier (21-23 DAE). The carbon compensation point occurred at eight or six leaves for C. arvense and T. farfara, with a total leaf area of 200 cm(2) for both species.