Physiological Integration among Intraclonal Ramets in Solidago Canadensis

Abstract

Clones of Solidago canadensis were studied to determine the degree of physiological interdependency among interconnected ramets. Ramets severed from their parental clone in the field experienced reductions in growth, survivorship and flowering, relative to intact controls. The results show that new daughter ramets are physiologically dependent upon resources translocated from their parental clone and that this dependency declines with time. When one of the ramets within each of several connected pairs was shaded to 10% of full sunlight, rates of photosynthesis increased in the remaining illuminated ramets. This and patterns of ramet survivorship and growth indicate that during periods of light limitation ramets become reintegrated. Shaded ramets become supported by the translocation of assimilates from other ramets within the clone. There is a tradeoff between rhizome number and length. When ramets become resource limited they produce fewer but longer new rhizomes. This results in the placement of daughter ramets at a location distant from the parent and may improve their probability of encountering more favorable conditions. The physiological integration among intraclonal ramets reduces the establishment risks of new daughter ramets and enables a genet to integrate local heterogeneity in resource availability. The result is that establishment and competitive ability are increased equitably among genets, and genets are buffered against localized patch—specific selection. This reduction in genetic deaths may be one mechanism resulting in the maintenance of variation in clonal populations.