Translocation of Photoassimilates Between Sister Ramets in Two Rhizomatous Forest Herbs

Abstract

Autoradiography and liquid scintillation techniques were used to trace the pattern of photoassimilate translocation in two perennial forest herbs, Aster acuminatus Michx. and Clintonia borealis (Ait.) Raf. Vegetative shoots of C. borealis emerge early each spring from the growing apices of a long-lived rhizome system. Vegetative shoots of A. acuminatus emerge in late spring from rhizomes that decay within 2 years. In both species ramets survive for only one growing season. Any connected plants are sisters. Mature leaves of these two species were exposed for 1 h periods to ¹⁴CO₂ during spring and summer. Radioactivity could subsequently be detected in exposed leaves (16–84 per cent, depending on the season), adjacent above ground plant parts (0.7–23 per cent), roots and rhizomes (4.9–84 per cent) and, when present, flowers (4–8.5 per cent). Old rhizomes of C. borealis are prominent storage sites for photosynthate. In A. acuminatus, no significant translocation between sister ramets (i.e. above ground shoots connected by a common rhizome) was observed. In C. borealis, there was small, but consistent translocation between sister ramets (0.2–4 per cent). Disturbance of unexposed sister ramets by defoliation, shading or herbivory increased the flow of photoassimilates to disturbed parts in C. borealis, but not in A. acuminatus. Based on the absence of translocation flow, ramets of A. acuminatus may be regarded as physiologically independent. Connected ramets of C. borealis show physiological integration. These results are correlated with ecological differences between the two species.