Compensatory mechanisms for reproductive costs in the dioecious tree Salix integra

In dioecious plants, females often incur greater reproductive costs than males, owing to the production of seed. This has led to evolution of cost-compensatory mechanisms in females. In trees, however, reproductive cost and compensatory mechanisms are not always detectable, probably because costs and compensation traits change with time, plant size, and modular level (i.e., individual shoots and whole plants). Herein we investigated sex-specific reproductive allocation, growth, and carbon acquisition mechanisms at different hierarchical levels in a dioecious tree, Salix integra Thunb. At both shoot and whole-plant levels, females invested more resources into reproduction than males, but without an associated reduction in vegetative growth, suggesting compensatory mechanisms in females. Females had greater biomass allocation to photosynthetic organs and higher photosynthetic rates than males. Although photosynthetic rates decreased with age, higher shoot turnover in females maintained higher productivity by consistently locating new leaves in favourable light. Females had larger areas of leafy bracts beneath peduncles, suggesting a reduction in the translocation distance of the assimilation to mature seeds. Females meet greater reproductive costs not by reducing growth, but by increasing the carbon uptake ability of different modular units in well-illuminated microenvironments.