不同光照强度下濒危植物景宁木兰幼苗光合特性的季节变化

  目的  探讨濒危植物景宁木兰Magnolia sinostellata在不同光照强度下光合能力的季节变化及适应机制，为种群的繁衍复壮和迁地保护等提供理论依据。  方法  以2年生景宁木兰幼苗为对象，在3种光照处理下(100%全光照、40%全光照和10%全光照)，对春季、夏季、秋季3个季节的光合特性指标进行了测定与分析。  结果  ①春季100%全光照和夏季100%全光照、40%全光照下净光合速率日变化均呈“双峰”曲线。②夏季100%全光照、40%全光照下最大净光合速率、光饱和点、光补偿点均显著高于10%全光照(P＜0.05)，而秋季100%全光照下最大净光合速率、光饱和点却显著低于40%全光照和10%全光照(P＜0.05)。③夏季、秋季100%全光照下最大电子传递速率和磷酸丙糖利用率均显著低于40%全光照(P＜0.05)。④100%全光照下光系统Ⅱ(PS Ⅱ)最大光化学量子产量在夏季、秋季分别为0.68和0.72。100%全光照下光化学猝灭系数和40%全光照下PSⅡ实际光化学量子产量在夏季均显著高于春季、秋季(P＜0.05)。  结论  在100%全光照下，景宁木兰易受夏季高温和强光胁迫，致使叶片灼伤，秋季净光合速率明显下降，而适当遮光条件下，景宁木兰在3个季节均能维持较高的净光合速率。因此，在景宁木兰栽培过程中，建议光合有效辐射保持在自然光照强度的40%以上。图5表1参23

Seasonal changes of photosynthetic characteristics of seedlings of Magnolia sinostellata under different light intensities

  Objective  This study, with an investigation of the seasonal variation of photosynthetic capacity and adaptation mechanism of Magnolia sinostellata, an endangered plant under different light intensity, is aimed to provide a theoretical basis for population reproduction and rejuvenation and ex-situ protection.   Method  With two-year-old seedlings planted under three light conditions, including 100% of natural light intensity, 40% of natural light intensity, and 10% of natural light intensity, their photosynthetic characteristics in spring, summer and autumn were measured respectively.   Result  (1) The diurnal variations of the net photosynthetic rate of M. sinostellata under 100% of natural light intensity in spring and 100% of natural light intensity and 40% of natural light intensity in summer were all featured with a bimodal curve. (2) The maximum net photosynthetic rate, light saturation point, light compensation point under 100% of natural light intensity and 40% of natural light intensity in summer were significantly higher than those under 10% of natural light intensity whereas the maximum net photosynthetic rate and light saturation point under 100% of natural light intensity in autumn were significantly lower than those under 40% of natural light intensity and 10% of natural light intensity (P＜0.05). (3) The maximum rate of electron transport and triose phosphate utilization rate under 100% of natural light intensity in summer and autumn were significantly lower than those under 40% of natural light intensity(P＜0.05). (4) Under 100% of natural light intensity, the maximum quantum yield of photochemical energy conversion (F_v/F_m) value was 0.68 in summer and 0.72 in autumn while the photochemical quenching and the effective quantum yield of photochemical energy conversion under 40% of natural light intensity in summer were significantly higher than that in spring and autumn (P＜0.05).   Conclusion  Under 100% of natural light intensity, the net photosynthetic rate of M. sinostellata seedlings in autumn significantly decreased, which might attribute to the damage done to leaves by the high temperature and high intensity of light in summer. However, M. sinostellata seedlings under proper shading could maintain relatively higher photosynthetic rate in three seasons. Therefore, it is recommended that photosynthetically active radiation at more than 40% of the natural light intensity is adopted in cultivation. Ch, 5 fig. 1 tab. 23 ref.]