HIGH-LEVELS OF INTER-RAMET WATER TRANSLOCATION IN 2 RHIZOMATOUS CAREXSPECIES, AS QUANTIFIED BY DEUTERIUM LABELING

We studied water translocation between interconnected mother and daugh ter ramets in two rhizomatous Carex species, using a newly developed q uantitative method based on deuterium tracing. Under homogeneous condi tions, in which both ramets were subjected either to wet or dry soil, little water was exchanged between the ramets. When the ramet pair was exposed to a heterogeneous water supply, water translocation became u nidirectional and strongly increased to a level at which 30-60% of the water acquired by the wet ramet was exported towards the dry ramet. T he quantity of water translocated was unrelated to the difference in w ater potential between the ramets, but highly correlated to the differ ence in leaf area. In both species, the transpiration of the entire pl ant was similar under heterogeneous and homogeneous wet conditions. Th is was a direct result of an increase in water uptake by the wet ramet in response to the dry conditions experienced by the interconnected r amet. In C. hirta, the costs and benefits of integration in terms of r amet biomass paralleled the responses of water consumption. This speci es achieved a similar whole-plant biomass in heterogeneous and homogen eous wet treatments, and water translocation was equally effective in the acropetal and basipetal directions. In C. flacca, responses of bio mass and water consumption did not match and, under some conditions, w ater translocation imposed costs rather than benefits to the plants of this species. It is concluded that enhanced resource acquisition by d onor ramets may be of critical importance for the net benefits of phys iological integration in clonal plants.