Gender-specific shoot structure and functions in relation to habitat conditions in a dioecious tree, Salix sachalinensis

In dioecious plants, females often incur greater reproductive costs than males due to seed production. This unequal reproductive cost can cause differences in the resource acquisition traits and the spatial segregation of the sexes. To evaluate how females compensate for the cost of reproduction, the differences in these traits between sexes were investigated in a dioecious tree, Salix sachalinensis, which is common in riverside forests. Females tend to inhabit the area near channel of rivers and streams and seem to be found at a lower ground level than males, indicating spatial segregation of the sexes. In the early growing season, females produced a greater number of vegetative shoots compared with reproductive shoots. In males the reverse was true, suggesting that females invest greater amounts of resources in photosynthetic organs than in reproductive organs at that time of the year. Females shed a greater number of vegetative shoots than males did during the growing season. In females, the shorter lifespan of vegetative shoots could enhance photosynthesis by placing new shoots in favorable light conditions. Both leaf weight ratio and leaf area ratio of vegetative shoots, and nitrogen content of the leaves, were found to be larger in females than males, but there was little difference in specific leaf area between the sexes. In females, shoot structure, phenology and physiology may compensate for their greater reproductive costs. Inhabiting wetter sites could result in a greater advantage to females than males, because such resources facilitate the photosynthetic capacity in females.