| Co-Investigator(Kenkyū-buntansha) |
HIKOSAKA Kouki TOHOKU UNIVERSITY, GRACUATE SCHOOL OF LIFE SCIENCES, ASSOCIATE PROFESSOR, 大学院・理学研究科, 助教授 (10272006)
WADA Naoya TOYAMA UNIVERSITY, FACULTY OF SCIENCE, ASSOCIATE PROFESSOR, 理学部, 助教授 (40272893)
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| Research Abstract |
Induced defense of plants, increase in fenolics and decrease in nitrogen following herbivory, is a widely recognized phenomenon in various plants. Influence of environmental clines on constitutive and induced defense of four species of Fagaceae species were studied. We tested a hypothesis that altitudinal-dependent outbreaks of the folivorous insects were caused by foliage properties in relation to environment clines along with altitude. Our results suggest that the foliage quality is one of the possible causes of site-dependent outbreaks of S. punctatella: During an increasing period, high quality food at outbreak sites promotes population growth of this insect. When beech trees suffer heavy defoliation in the non-outbreak areas, foliage quality deteriorates, which slows down S. punctatella population growth. In contrast, in outbreak areas, quality increases in the year following heavy defoliation, and this may promote population growth and outbreaks. A positive feedback process thus may operate among nutrient cycling, foliage quality and insect population growth. A fertilizing effect from herbivory was a proximate factor causing higher soil nitrogen availability in the outbreak area. Results of our experiment suggested that the amount of defensive compounds was controlled by the carbon-nutrient balance at a leaf level. The C/N balance is an important factor for biomass allocation and chemical defense. However, the effect of defoliation on the C/N balance in a plant is variable between species, probably leading to a species variability in herbivory responses.
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