THE COMMUNITY STUDY ON INTERACTION AMONG NUTRIENT CYCLE, ANIMALS, AND PLANTS

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The purposes of this research are to clarify the effects of soil fertility on 1)plant growth and phenotypic plasticity, 2)community structure of herbivory and predators, and 3)flows and stocks of nutrient cycles. Quercus serrata and Q.crispula saplings were grown in herbivore-damaged or undamaged areas of the greenhouse with the two fertilization treatment levels, low or high.At the individual level, herbivore-damaged saplings exhibited a significant increase in leaf numbers ; however, the total length of the extension units (EUs) in Q.serrata or Q.crispula was not significantly affected by herbivore damage, regardless of soil fertility. Furthermore, the probability of flushing in Q.serrata increased with an increase in the leaf damage of the parent EU. These results suggest that Q.serrata or Q.crispula saplings produce shorter EUs in response to herbivore damage in order to reduce the cost of mechanical support and spread the risk for any subsequent herbivore damage.For Q.serrata, ins … More ect damage significantly reduced leaf biomass at high soil fertility at the shoot and individual level. For Q.serrata, insect damage reduced leaf biomass regardless of soil fertility at both levels. Condensed tannin concentrations were high in saplings receiving insect damage at low soil fenility in both species. These results were likely to reflect a species-specific growth strategy ; Q.serrata invests in photosynthetic tissues and higher leaf quality, while Q.serrata invests in non-photosynthetic tissues.The difference of soil nutrient contents (three-year passed after transplanted) between insect damaged and undamaged soil on the experimental plot were analyzed to clarify the effect of insect damage on soil nutrient cycles. Water-extractable organic carbon (WEOC), nitrogen concentration, nitrogen mineralization rate, and nitrification rate were measured in vitro. The concentration of WEOC on insect damaged soil was higher than that on insect undamaged soil, whilst the effects of insect damage on the other nutrients were not observed. WEOC generally plays an important role on speed of nitrogen minedization in soil. Therefore, the results obtained here imply that long-term insect damage gives large impacts on nutrient cycles in soil. Less