Photosynthesis and growth of newly established shoots of Cirsium arvense and Tussilago farfara are resource independent

P>Cirsium arvense and Tussilago farfara are noxious creeping perennial weeds of temperate crops. Cirsium arvense infests both conventional and organic crops, while T. farfara is more common in organic cropping systems. Mechanical control used in organic farming often leaves intact shoots within crop rows. It is unknown whether shoots and rhizomes are affected by cutting adjacent interconnected shoots. In glasshouse experiments, comparison of net photosynthesis, chlorophyll a fluorescence and quantum efficiency (Fv/Fm) of disturbed and undisturbed clones, did not show any disturbance effect. Maximum net photosynthesis decreased over time in both disturbed and undisturbed clones, depending on environmental conditions. Maximum net photosynthesis was not affected by the size of removed shoots and the Fv/Fm did not change much from the theoretical value of 0.83. These results imply that there were no source/sink relations in established shoots acting as feedback control for photosynthesis. The resource sharing via horizontal roots/rhizomes did not exist at the rosette growth stage in homogeneous environments. Therefore, both species do not benefit from their clonal interconnectedness as perennial weeds to cope with disturbances, as compared with annual weeds. Further studies are required to investigate this in heterogeneous environments.