Ecophysiology of the sand sedge Carex arenaria L. II. The distribution of 14C assimilates

14C assimilates produced in a single shoot of a sand sedge plant proved to be translocated in the direction of the rhizome tip only. Labelled assimilates were found in all roots in the part of the plant system between the shoot administered with 14C02 and the rhizome tip, in the youngest shoot and in the rhizome tip itself. The percentage of assimilates exported by the mature shoots proved to be 30-35%. The amount of assimilates exported by the youngest shoot decreased from 22% in a 1-shoot system to zero in the bigger plant systems. In the 5-shoot system also the export of the second youngest shoot started to decrease. In spite of the relatively great sink strength of the rhizome tip with regard to the assimilates exported by the nearby situated young shoots, the main source of assimilates for the rhizome tip proved to be the older shoots, lying at some distance. The ecological importance of this is that the rhizome tip will be able to cross unfavourable habitats, without the need for assimilates from the newly formed shoots in those habitats.