Seasonal patterns of partitioning and remobilization of C-14 in the invasive rhizomatous perennial Japanese knotweed (Fallopia japonica (Houtt.) Ronse Decraene)

Resource partitioning between shoot growth, storage and reproduction is poorly understood in many clonal plant species. This study documents seasonal patterns of growth, C-14-labelled photoassimilate distribution and remobilization in the invasive rhizomatous species Fallopia japonica (Japanese knotweed). Biomass accumulation above- and below-ground in F. japonica was rapid. By September, rhizome biomass had increased 18-fold from the initial harvest in May (representing 48% of total plant biomass) and this was maintained over winter. Patterns of C-14 allocation from F. japonica shoots labelled at different times of year show that as the season progressed, the rhizomes became an increasingly important sink for current assimilate (the percentage of C-14 recovered from rhizomes was 35% in August and 67% in September) and the corresponding retention of assimilate by established shoots declined. The percentage of C-14 exported to roots was greatest in August. Relatively little photoassimilate was exported to other shoots on the plant, or to flowers. Recycling of photoassimilate was fairly tight in this species and C-14 fixed by shoots in early May 1999 or September 1999 was remobilized to the rhizome prior to shoot senescence and death. Some of this C-14 was then remobilized to new shoots early the following spring. These characteristics may contribute to the success of F. japonica in colonizing a variety of contrasting habitats, often with serious management implications.