Relationship between the composition and distribution of nutritional substances, secondary metabolites, and internal secretory structures in the bark tissues of Larix gmelinii var. japonica, L. kaempferi, and their F-1 hybrid and susceptibility to vole herbivory

摘要

We investigated the quantitative composition and distribution of nutritional substances (soluble sugars, starch, and protein), secondary metabolites (terpenoids and phenolic compounds), and the length, area, and density of internal secretory structures (resin ducts and cavities) in the rhytidome (outer bark) and secondary phloem (inner bark) of Kuril larch (Larix gmelinii var. japonica), Japanese larch (L. kaempferi), and their F-1 hybrid (L. gmelinii var. japonica x L. kaempferi) in order to clarify the relationship of these parameters to susceptibility to red-backed voles' herbivory in Hokkaido, Japan. The amounts of most nutritional substances in each of both bark tissues were not significantly different among the three larch taxa. The amounts of carane-type monoterpenoid and labdane-type diterpenoid in both bark tissues of L. gmelinii var. japonica and the F-1 hybrid were significantly higher than those of L. kaempferi. The amounts of phenolic compounds in both bark tissues of L. gmelinii var. japonica were significantly lower than those of L. kaempferi. The quantitative composition of most secondary metabolites in both bark tissues of the the F-1 hybrid were between L. gmelinii var. japonica and L. kaempferi. The area and density of the resin ducts and cavities, which were containing terpenoids, in both bark tissues of L. gmelinii var. japonica and the F-1 hybrid were significantly larger and higher than those of L. kaempferi. These results suggest that L. gmelinii var. japonica and the F-1 hybrid utilize some predominant constitutive mono- and diterpenoids as chemical defensive substances in the bark tissues against the voles.