光照强度对大豆叶片光合特性及同化物的影响

间套作荫蔽环境下, 光强是影响作物生长和产量的直接因素。本试验通过设定不同光照强度, 分析不同大豆品种的光合特性、光合同化物和叶片中叶绿体超微结构的昼夜变化, 明确光强对大豆叶片结构和同化物积累的影响, 了解品种间差异, 以期为提高大豆产量、改善大豆品质提供理论依据。以耐阴品种南豆12和敏感品种桂夏3号为试验材料, 分别设置CK (正常光照, 遮光度0)、A1 (一层黑色遮阳网, 遮光度10%)、A2 (两层黑色遮阳网, 遮光度36%) 3个不同光照强度。结果表明, 随着遮阴程度的增加, 2个大豆品种净光合速率、气孔导度、蒸腾速率和生物量均呈逐渐降低趋势, 但胞间二氧化碳浓度、叶绿素b含量逐渐上升。同一大豆品种在相同处理下叶片蔗糖和淀粉含量昼夜变化差异显著。正常光照和A1处理下的大豆叶片蔗糖含量昼夜变化呈双峰曲线, 波峰分别出现在16:00和次日6:00, A2处理下南豆12蔗糖含量昼夜变化呈单峰趋势, 峰值出现在16:00, 为32.80 μg g ^-1。淀粉含量昼夜变化呈单峰曲线, 最高值均出现在21:00, 且耐阴品种大豆在A2处理下蔗糖和淀粉含量日变化幅度大于敏感品种大豆。大豆叶片超微结果表明, 弱光处理下大豆叶片叶绿体结构完整, 无破碎现象, 相同品种在同一处理下淀粉粒与叶绿体截面积比值昼夜变化显著, 均呈先增加后降低的变化趋势, 耐阴品种变化幅度大于敏感品种, 最大值均出现在21:00。因此, 随着遮阴程度增加, 大豆叶片生物量积累减少, 光合作用降低, 但耐阴品种在适度遮阴下通过调节光合器官结构的昼夜变化而保持良好的光合作用, 以更好地适应荫蔽环境。

Effects of Light Intensity on Photosynthetic Characteristics and Assimilates of Soybean Leaf

Light intensity plays a significant role in determining the growth and seed yield of crops under the sheltering of intercropping systems. By setting different light intensities, the photosynthetic characteristics, assimilate metabolism and the diurnal variation of chloroplast ultrastructure in leaf of different soybean cultivars to clarify the effect of light intensity on the structure of soybean leaf and the accumulation of carbohydrate, in order to provide a theoretical basis for improving soybean yield and quality. A pot experiment was carried out with three light intensities treatments, including CK (normal light, shading 0), A1 (black shading net, shading 10%) and A2 (two black shading nets, shading 36%) of two soybean cultivars (shade-resistant cultivar Nandou-12 and shade susceptible cultivar Guixia-3). With increased shading, net photosynthetic rate, stomatal conductance, transpiration rate and biomass decreased while intercellular carbon dioxide concentration and chlorophyll b increased in all treatments. There was a significant difference in the diurnal variation of sucrose and starch contents in soybean leaf under the same treatment. The diurnal variation of sucrose content in soybean leaf showed a bimodal curve with the peaks at 16:00 and next day 6:00 respectively under CK and A1 treatment. Under A2 treatment, the highest diurnal sucrose content was 32.80 μg g ^-1 in Nandou 12 and showed a unimodal changing trend with the peak at 16:00. The diurnal variation of starch content showed a single-peak curve and the highest value appeared at 21:00. Compared with the shade sensitive cultivar, the shade-tolerant soybean had greater diurnal variation of sucrose content and starch content under A2 treatment. The chloroplast structure of soybean leaf was intact and unbroken under the low light treatment. The diurnal variation of the cross-sectional area ratio of starch grain to chloroplast in the same cultivar changed significantly under the same treatment, showing a trend of decreasing after increasing. The changing rate was greater in shade-tolerant cultivar than in sensitive cultivar, and the maximum value appeared at 21:00. Therefore, biomass accumulation of soybean leaves and photosynthesis decreased with increasing shading. However, shade-tolerant cultivar maintained a good photosynthesis by adjusting the diurnal variation of photosynthetic organ structure, thus better adapting to the moderate shading condition.