关键词: 黄叶植物, 遮荫, 叶色, 色素含量, 生理指标, 光合特性, 叶绿体超微结构

Abstract:

Objective: In this study, we investigated the effect of different shading intensitieson leaf color and related physiological indexes of Ulmus pumila 'Jinye' and Koelreuteria paniculata 'Xinye', to explore and compare the physiological mechanism of the color generation of the two yellow leaf plant species. This study aimed at maximizing the garden application and providing the oretical basis for yellow leaf plants to be planted in places where sunlight is insufficient or the light is shaded. Methods: One-year-old U. pumila 'Jinye' and K. paniculata 'Xinye' were subjected to different light intensities, i.e. natural illumination, 20%, 50% and 90% shading conditions, for two months, and leaf color, content of photosyn the ticpigments, photosynthetic fluorescence parameters, leaf reflection spectrum, leaf shape and organic matter contents of the two yellow leaf plants were examined, and the chloroplast ultrastructure was observed at the subcellular level. Results: Under the natural illumination, the leaf color of U. pumila 'Jinye' was golden yellow, and that of K. paniculata'Xinye' wasgreenyellow. With the increasedshading degree, the leaf color of the two plants turned green gradually. The leaf color of U. pumila 'Jinye' turned greenobvious, andits yellow-blue parameter (b^*) value decreased from 70.42 to 47.27 under 90% shading condition. The leaf color of K. paniculata 'Xinye' turned slightly greenish. Under 90% shading condition, the b^* value decreased from 65.69 to 58.34and the leaf color remained yellowgreen compared with the control (full natural illumination) group. With the increase of shading ratio, the chlorophyll contents of the two yellow leaf plants increased significantly, the photosynthetic rate and spectral reflectance decreased, the Chl a/b, specific leaf weight, PSII maximum photochemical efficiency (F_v/F_m), maximum fluorescence (F_m) of the two plants were significantly increased. The spectral reflectance of leaves of the two species decreased under the shade environment, and the red edge parameter indicated the light stressof U. pumila 'Jinye'in natural illumination. The structure of thylakoids of the two species also changed greatly under shading conditions. The number of thylakoids and stacking layers in chloroplasts increased, and the thylakoid in chloroplast changed from curved lamella to parallel stack-like granules. Under different shading conditions, there was no significant change in content of soluble sugarsin U. pumila 'Jinye', the soluble protein content was significantly decreased, the leaf areas were significantly increased, and the leaf length-width ratio did not change significantly. For K. paniculata 'Xinye', there was no significant difference in soluble sugars and soluble protein contents under 20%shadingconditioncompared with the control. The contents of soluble sugars and soluble protein under 90% shading condition were significantly lower than those of the control, and the leaf shapes were not significantly different before and after shading. Objective: The leaves of U. pumila 'Jinye' and K. paniculata 'Xinye' were brighter and yellower in the natural condition, however the two species were inhibited to some extent by light. With shading ratio increased, the photosynthesis rate of the two species decreased, the thylakoids were stacked, and the leaf colors returned green in different degrees. Under 20% shading condition, the growth and leaf color of U. pumila 'Jinye' were less affected, the leaf color remained yellowgreen.The 50% and 90% shading conditions were unfavorable for yellow leaf and photosynthetic product accumulation. The leaf color of K. paniculata 'Xinye' turned green slightly under different shadingratio conditions, and was still in the yellow leaf category, but 90% shading condition had serious influence on its photosynthetic physiology. Therefore, from the perspective of growth and leaf coloration, the natural illumination is the best illumination condition for both of U. pumila 'Jinye' and K. paniculata'Xinye', and they can be planted in a suitable shading environment according to their respective physiological characteristics.

Key words: yellow leaf plants, shading conditon, leaf color, pigment content, physiological indexes, photosynthesis characteristics, chloroplast ultrastructure