Sexual differences in physiological integration in the dioecious shrub Lindera triloba: a field experiment using girdling manipulation

Background and Aims It is important to consider the modular level when verifying sexual dimorphism in dioecious plants. Nevertheless, between-sex differences in resource translocation among modules (i.e. physiological integration) have not been tested at the whole-plant level. In this study, sexual differences in physiological integration were examined among ramets, within a genet in the dioecious sprouting shrub Lindera triloba, by a field experiment with girdling manipulation. Methods Female and male genets were randomly assigned to girdled or intact groups. Girdling of the main ramets was conducted in May 2009 by removing a ring of bark and cambium approx. 1 cm wide at a height of 80-100 cm. The effects of treatment and sex on ramet dynamics (mortality, recruitment and diameter growth) and inflorescence production during 1 year after girdling were examined. Key Results The diameter growth rate of main ramets of both sexes was lower at ground level (D-0) but higher at breast height (dbh) in girdled than in intact groups. In sprouted ramets with a dbh of 0-2 cm, males in girdled groups had lower growth rates at D-0 than those of intact groups, whereas no girdling effect was found for females. The main ramets in girdled groups produced more inflorescences than intact groups, irrespective of sex, but male ramets showed a greater response to the treatment than females. Conclusions In L. triloba, physiological integration exists at the whole-plant level, and sprouted ramets are dependent on assimilates translocated from main ramets, but this dependence weakens as sprouted ramets get larger. Female sprouted ramets can grow in a physiologically independent manner from the main ramet earlier than those of males. This study highlights the importance of considering modular structures and physiological integration when evaluating sexual differences in demographic patterns of clonal plants.