地球環境科学研究科 植物生態学セミナー 2006-10-31 (火) 10:30

The relationships between leaf longevity and other leaf traits in a tropical montane forest on Gunung Halimun, West Java

塩寺さとみ

In the tropical regions, many plant species live together to form rainforest ecosystems. Human-caused disturbance and destruction on forest ecosystems cause serious problem particularly in species-rich tropical regions. It is an important question to be answered how so many species coexist in rainforests and how forests will change in future. Reich et al. (1991) studied the relationships between photosynthetic rate and leaf traits from the view of ecophysiology in Venezuela, indicating strong correlations between leaf longevity, photosynthetic rate and leaf N concentration. They studied only tree species and the role of ecological differentiation across functional types in a particular community is not yet fully demonstrated. Functional types have often been related to physiognomy of plants, based on the assumption that architecture is more or less related to them. However, studies that relate ecophysiological diversity and architectural diversity remain rare. When plants are compared among life forms or functional types, turnover rate, nutrient concentrations and defensive compounds of leaves can be different reflecting their respective ways of adaptation. The purpose of this study is to describe the relationships between leaf longevity and leaf traits (morphological, physiological and demographical) through comparing species and functional types in a montane rain forest. We carried out leaf phenological monitoring over 2.5 years and measured leaf traits of 104 understorey species with varying life forms.

Survival analysis indicated that LMA (leaf mass per area, g cm-2) gave a positive influence, while leaf size, total phenolics (condensed tannin free) and condensed tannin had negative effects on the risk of leaf mortality. Number of leaves and longer flushing interval increased leaf longevity. Leaf size, LMA, Nmass (mass-based leaf N concentration) and total phenolics (condensed tannin free) facilitated leaf herbivory. The influences of each covariate factor were decreased in order LMA, leaf size, leaf position and Nmass. Older leaves received more damage than younger ones. High leaf toughness and condensed tannin reduced the degree of herbivory. In the comparison between functional types, the distribution of each leaf traits did not show remarkable differentiations. However, climbers indicated larger mean leaf longevity and lowest herbivory ratio. Whereas trees showed a broad range of leaf longevity in species comparison, in spite that they showed the shortest longevity and highest herbivory ratio on an average. From these results, we conclude that each functional type develops a wide and overlapped range of variety in leaf traits based on physiological rule. Each species has remarkable differentiation not only between but within functional types being reflected the coexistence under the understorey environment.


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