Seasonal Variations in Canada Thistle (Cirsium arvense) Root Bud Growth and Root Carbohydrate Reserves

Abstract

Canada thistle [Cirsium arvense(L.) Scop. # CIRAR] root samples were collected at monthly intervals over a 2-yr period from two locations to determine seasonal fluctuations in the presence and growth potential of root buds. Root bud growth was highest during late fall and winter months following death of the aerial shoots. Root fragments incubated at a constant 15 C for 2 weeks in continuous light consistently had more buds than nonincubated roots, which indicated active bud differentiation during the incubation period. Incubated roots produced 3 to 9 cm of new shoot length/cm root length. There were no obvious seasonal patterns in the presence of root buds or their ability to elongate at different times of the year. Carbohydrate reserves were stored preferentially in roots rather than in developing root buds or the bases of shoots. These reserves ranged from as low as 3% of root fresh weight during spring months to as high as 26% in late fall months, although the levels did not increase consistently during summer months over the locations and years of this study.