| Summary: | 碩士 === 國立臺灣大學 === 生態學與演化生物學研究所 === 102 === Setaria palmifolia (Poaceae) is a common tall grass in Taiwan. Because aborigines believed that cross-markings on its leaves can be used to forecast occurrence of typhoons of the year, it is locally called “tai feng cao”. This plant is recorded as a C4 plant, which is commonly adapted to high light and high temperature environment, growing in varied light environment at field. In this thesis, the number and distribution pattern of cross-markings on the leaves of S. palmifolia plants in different environments, and the formation of cross-markings were studied. The shade-tolerant mechanisms of the plant were also investigated. During the experiment, that leaves showed changing of brightness after illuminating with different intensities of light. This phenomenon was also explored.
Morphological and anatomical features, optical properties and physiological performance of field growing and greenhouse grown plants were analyzed. The cross-markings on leaves of S. palmifolia can be classified into two types, folding and wrinkles. Each leaf had only one folding but numerous wrinkles. Measurements on field growing and greenhouse grown plants revealed that S. palmifolia plants under different environment grew different length of leaf blade. The distance between the folding and proximal end of the leaf blade was significantly positive correlated with the length of leaf blade, while the relative location of folding was negatively correlated with the length of leaf blade. However, the number and distribution pattern of wrinkles were more complex than those of foldings.
No difference was found in cross sections between the part of folding (or wrinkles) and other part of leaves. Paraveinal sections revealed that the formation of folding was due to leaf tissues being compressed upward, while that of wrinkles being pressed concavely. Therefore, the formation of the two types of cross-markings might be induced by different forces. After investigating developing leaves, the formation of folding on developing leaf was caused by wrapping and compressing of ligule of the previous leaf. While the formation of wrinkles can’t be telled from current observation.
Phenotypic plasticity was found in S. palmifolia plants grown in different light environment. Plants in shady treatment had significantly larger leaf area per dry mass (SLA) and thiner leaves than those received full sun light treatment. An increased in SLA would increase light intercepting area with the same amount of biomass allocating which might benefit S. palmifolia growing under low-light condition. Significantly higher photosaturated photosynthetic rate and higher light saturation point were measured on plants received full sun light treatment than shady treatment. Mesophyll chloroplasts of S. palmifolia showed avoidance response (resulting in increment of transmittance) under illumination of light intensities higher than 700 μmol m-2 s-1, while showed accumulation response (resulting in reduction of transmittance) at light intensities lower than 300 μmol m-2 s-1. The behavior of chloroplast movements may optimize photosynthetical light use efficiency of leaves under low-light conditions while reduce the risk of photodamage of leaves under high light stress. Phenotypic plasticity and chloroplast movement response confer S. palmifolia ability to grow under varied light environment.
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