Chemical Ecology of an Invader (Podocarpus Nagi)

1991 Fiscal Year Final Research Report Summary

• Project/Area Number: 01480007
• Research Category: Grant-in-Aid for General Scientific Research (B)
• Allocation Type: Single-year Grants
• Research Field: 生態学
• Research Institution: Osaka City University
• Principal Investigator: YAMAKURA Takuo Osaka City Univ., Dept. Biol., Ass. Prof., 理学部, 助教授 (10089956)
• Co-Investigator(Kenkyū-buntansha): KAWAGUCHI Hideyuki Kyoto Univ., Dept. Agri., Ass., 農学部, 助手 (40202030) ; KANAZAKI Mamoru Osaka City Univ., Dept. Biology, Ass., 理学部, 助手 (70183291) ; TANIGUCHI Makoto Osaka City Univ., Dept. Biol., Ass., Prof., 理学部, 助教授 (00047309) ; YODA Kyoji Osaka City Univ., Dept. Biol., Prof., 理学部, 教授 (80046937)
• Project Period (FY): 1989 – 1991
• Keywords: Chemical Ecology / Nagi-Lacton / Allelopathy / Chemical Defense / Ecological Invasion

Research Abstract

A podocarp forest with Podocarpus nagi dominant covers the west slope of a small hill, Mt. Mikasa with a peak of 294 m in altitude, situated on the north-eastern part of Nara City, the capital of Nara Prefecture, Central Japan. It has been protected for a background of the Kasuga Shinto Shrine through long historical time over 1400 years. Since some podocarp trees was artificially planted on a foot of the hill about a thousand years ago to express man's respect to the Shinto Gods, the trees has been invading into the native vegetation, Japanese broadleaved evergreen forest. This invader is aggressive to other plants owing to its allelopatic chemicals, Nagi-lactones with six optical isomers. This study is concerned with chemical ecology of a life strategy adopted by an aggressive invader P. nagi.
The chemicals clearly inhibited the germination and initial growth of native trees and released P. nagi from grazers, whose major component was one thousand deers living in the forest and has been protected as a holly animal of the Shinto Gods at the Shrine. There was substantia '1 flow of chemicals from forest canopy to forest floor in litterfall and the others : throughfall and stemflow in rain. Therefore the cycle of the chemicals in the forest ecosystem was highly correlated with carbon and nutrient cyclings, suggesting the auto-intoxication of the invader.
Forest soil was polluted by the chemicals and resulted in the poor forest architecture and frolal composition. The invader is a monoecious species with a sex ratio of 1 : 1. The distribution pattern of seedlings of the invader depend on the male trees. The phenological phenomena of the invader suggested its tropical origin and its mast fruiting was observed every four years implying the high correlation with the ENSO.