Abstract:

To reveal the photosynthetic physiological characteristics and select the best fitting model to analyze the photosynthetic-light response curve of Buddleja officinalis Maxim. in different habitats, the plant high, basal diameter, leaf area, inflorescence ength,flavonoids,photosynthetic characteristics (using a portable photosynthesis system LI-6400 to measure photosynthetic light response curves and diurnal variations of photosynthesis) and chlorophyll contents in canopy gap, forest edge and forest understory were measured and compared. The results showed that the plant high, basal diameter, leaf area, inflorescence length and flavonoids were the highest in the canopy gap (P<0. 05). The chlorophyll-a, chlorophyll-b, and total chlorophyll contents were the highest in the canopy gap, and the lowest in the understory (P<0. 05). The diurnal variation of the net photosynthesis rates in the leaves of B. officinalis in the canopy gap and understory showed one-peak curve, whereas at the forest edge it showed a double-peak curve with remarkable midday depression. The modified rectangular hyperbola model was the best fitting model for the light response curve of B. officinalis, and the light saturation intensity in three different habitats were 1 424. 70, 1 725. 76, and 1 608. 85 μmol/ (m2·s), respectively; the maximum net photosynthetic rates were 14. 07, 17. 54, and 16. 30 μmol/ (m2·s), respectively; and the light compensation points were 26. 59, 19.08 and 20. 89 μmol/ (m2·s), respectively; which were consistent with the characteristics of semi-negative to semi-positive plants. The lower light compensation point and higher light saturation point occurred in the canopy gap, indicating that B. officinalis in canopy gaphad wider ecological amplitude to light than that other habitats. B. officinalis had the characteristics of combining shade plant and heliophyte,and the canopy gap habitat might be helpful to accumulation of organic materials and more suitable for the growth. Planting in the understory habitat needs to improve canopy light penetration in time, then at the forest edge, the appropriate shading is required.

Key words: Buddleja officinalis Maxim. , chlorophyll content, light response curve, diurnal variation of photosynthesis