Michinari Matsushita

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.

Interactive Effect of Canopy and Fluvial Disturbances on Sapling Community Structure and Species Diversity in a Montane Riparian Forest1

Abstract: Montane riparian forests exhibit a higher diversity of tree species than adjacent stands. This pattern is thought to be generated by the unique disturbance regime of riparian forests, including canopy gap formation and fluvial disturbance (e.g., transport of boulder/gravel sediments), which provides a variety of habitat conditions for regeneration (habitat niche segregation). Although segregation of micro-environmental conditions for seedling establishment has been confirmed, habitat segregation for saplings remains untested. Thus, to determine if the composition and structure of the riparian sapling community is influenced by canopy and fluvial disturbances, we sampled 11 canopy-gap sites and 3 fluvial boulder-deposit sites, as well as beneath-canopy sites that had not been disturbed recently, in a temperate mixed-species deciduous forest. We analyzed the distribution patterns of saplings for 31 canopy and subcanopy species. Saplings were found mainly on the disturbed sites compared with the beneath-canopy sites. A comparison of relative densities for 13 major species in gaps versus on fluvial deposits revealed that 5 species were biased significantly to gaps and 4 species to fluvial deposits. Cluster analysis detected 4 species groups with different light requirements. These results suggest riparian habitat partitioning between species through differentiated preferences for the disturbance type × light requirement combination.

Inter-specific and sexual differences in architectural traits of two dioecious Lindera species (Lauraceae)

The architecture of trees is a crucial determinant of their performance through light capture and mechanical stability. Comparison of architectural traits between closely related dioecious species is predicted to reveal both inter-specific and sexual differences. The former may reflect life-history characteristics such as microhabitat preferences, and the latter may reflect costs of reproductive allocation. We measured branching structure, leaf traits, wood density, and biomass of each vegetative component in the dioecious shrubs Lindera praecox and Lindera triloba to explore architectural differences according to species and gender. L. triloba was less branched but had a greater total leaf mass per shoot having larger and heavier leaves than L. praecox; most of these traits did not differ by gender. Allometric relationships between height and branch biomass corroborated our results of branching structure. The allometric relationships between tree size and leaf biomass demonstrated that in larger size classes females of both species had greater leaf biomass than males. Females of both species also showed lower tree height than males. This study suggests that tree architecture is influenced by both life-history strategy and resource-allocation pattern. Branching structure and branch biomass showed inter-specific differences, with the highly branched L. praecox apparently more shade tolerant than L. triloba; its tolerance is likely adaptive in its preferred microhabitat where is often lit poorly. Sexual differences in leaf biomass and tree height growth may reflect higher reproductive costs incurred by females.

Sampling design for efficient detection of pine wood nematode, Bursaphelenchus xylophilus , in diseased trees using a DNA detection kit: variation across branch, trunk and tree

Detection of pine wood nematode, Bursaphelenchus xylophilus , is fundamental for effective control of pine wilt disease. Recent molecular techniques, such as DNA detection, have enhanced detectability of the nematodes whereas appropriate field sampling has received less attention. In order to elucidate a sampling design that most efficiently detects B. xylophilus using a commercially-distributed DNA detection kit, we compared detection levels of B. xylophilus using wood chips taken from various positions on dead trees. Results showed that the DNA kit had a higher detection level than the conventional method, and that trunk samples had higher levels than branch samples. Statistical model revealed that among-tree variation influenced the detectability more strongly than within-tree variation. Our results suggest that, in practice, with limited resources for control, it is more efficient to take samples from many trees with a minimum number from each tree, rather than taking many samples from a small number of trees.