| Summary: | 碩士 === 國立臺灣大學 === 生態學與演化生物學研究所 === 105 === C4 plants are mainly distributed in habitats with high light and high temperature. Setaria palmifolia, a C4 plant, can grow in a broad range of light environments, such as in forest edge and understory. A previous study implied that phenotypic plasticity and chloroplast movement response confer S. palmifolia ability to grow under varied light evironments. Leaf characters, photosynthetic performances and growth of three C4 plants, S. italica (distributed in open habitat), S. palmifolia (in forest edge and understory) and S. plicata (mainly in understory), grown under different light regimes were measured in this study. The relative distance plasticity index (RDPI) was calculated for the comparison of phenotypic plasticity among the studied species. Chloroplast movements and photosynthetic induction response were also investigated to evaluate whether shade-tolerant S. palmifolia and S. plicata have more apparent chloroplast movements and better efficiency in utilizing sunflecks than S. italica.
Results showed that leaf size of S. italica decreased but that of S. palmifolia and S. plicata increased (both with similar magnitude of response) as growth light level decreased. As growth light level decreased, the three species showed reduction in mesophyll thickness, chlorophyll a / b ratio (S. italica the highest response), respiration rate and light compensation point, while increased in specific leaf area, chlorophyll content per unit mass (S. plicata the highest response) and aboveground to belowground biomass ratio. Overall, S. italica had the highest RDPI, and S. palmifolia the lowest. In comparison of the three species, S. italica had the largest leaf size, photosynthetic capacity and light saturation point under full-sun regime while S. palmifolia had the largest leaf size under intermediate and low light regime. Under low light regime, S. plicata had the lowest respiration rate and light compensation point.
Three species had blue light induced chloroplast movements (accumulation and avoidance response). Apparent chloroplast movements (accumulation response) were found in leaves of full-sun grown plants. S. palmifolia and S. plicata showed significant avoidance response when they were grown under low light regime. The avoidance response of chloroplast might reduce the risk of photodamage caused by excessive light (e.g., sunflecks) when S.palmifolia and S. plicata growing in forest understory. Three Setaria species had rapid photosynthetic and stomatal responses in response to changes in light intensity, from 20 to 1600 μmol m-2 s-1. When grown under shaded environment, S. palmifolia achieved light-saturated photosynthetic rates in relatively shorter time than the other two specise. Accordingly, S. palmifolia might have better efficiency in utilizing sunflecks than the other two species.
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