Stolons and rhizomes may be important for the placement of leaves and roots in new microhabitats (foraging), as well as for the storage of resources. In a species which forms both types of structures, such as Cynodon dactylon, both such functions could be combined in a single structure, or rhizomes and stolons could exert different functions. We examine these functions in C. dactylon, by investigating plasticity in morphology and biomass allocation in response to variation in light and nutrient availability. Both stolon and rhizome branching intensities were reduced in response to lower light and lower nutrient levels. Stolons and their internodes elongated greatly under lower light levels, but slightly shorter under lower nutrient levels. The lengths of rhizomes and their internodes did not respond significantly to nutrient availability. Only at low light levels did the plant form orthotropic shoots. Rhizomes failed to develop, and biomass allocation to stolons was slightly lower under low compared to high light intensity. The morphology of stolons was more responsive than the morphology of rhizomes to resource supply. Biomass allocation to stolons, however, was less variable than allocation to rhizomes in response to light and nutrient treatments. These results support the contention that stolons enable C. dactylon to forage for light while rhizomes serve as organs for storage of resources and meristems. These results are interpreted in terms of the efficiency of exploitation of light patches within the habitat of C dactylon, and the ability to survive after unpredictable disturbances.
