光强对砂仁叶片光合作用光抑制及热耗散的影响

EFFECTS OF LIGHT INTENSITY ON PHOTOINHIBITION OF PHOTOSYNTHESIS AND THERMAL DISSIPATION IN AMOMUM VILLOSUM LOUR.

通过测定不同光照条件下砂仁 (AmomumvillosumLour.)叶片气体交换和叶绿素荧光参数 ,探讨了光对其光合机构及其光破坏防御的影响。试验期间 ,上午 11:0 0之前有雾 ,光强较弱。上午砂仁阳生叶净光合速率 (Pn)与下午 (6 .5 3μmol·m-2 ·s-1)相似 ,高于阴生叶 (5 .94μmol·m-2 ·s-1) ,下午阴生叶Pn 高于上午 ,与阳生叶相似。下午砂仁叶片表观量子效率低于上午。其初始荧光 (Fo)、最大荧光 (Fm)、光系统Ⅱ (PSⅡ )最大光能转换效率 (Fv/Fm)、Fm/Fo 及PSⅡ的潜在效率 (Fv/Fo)随日光增强而降低 ,15 :0 0降至最低 ,表明光抑制逐渐加剧。之后随光强减弱这些叶绿素荧光参数升高 ,光抑制得到缓解。与此相反 ,非光化学猝灭系数 (qN)随光强的增加而升高 ,并一直维持在较高水平 ,表明依赖叶黄素循环的保护性反应逐渐增强。阳生叶的光抑制比阴生叶强烈 ,当日遮荫处理使光抑制缓解 ,但各处理间qN 差异不大 ,表明热耗散未受显著影响。结论 :弱光下砂仁叶片即发生光抑制 ,在不同光照下其光抑制的普遍发生 ,是依赖叶黄素循环的保护性反应 ,而非光破坏的结果 ;砂仁叶片叶黄素循环的启动不需过剩光能 ,不同光处理对其影响不大 ;砂仁对光的适应能力较强。

Amomum villosum Lour.(Zingeraceae) is a perennial herb that occurs in the understory of tropical and subtropical forests. It is an important medical plant too. Its leaves naturally roll up upon exposure to bright sun. Gas exchange and chlorophyll fluorescence parameters were determined with a Li_Cor 6200 photosynthesis system and a modulated chlorophyll fluorescence monitoring system (FMS 2.02) in order to explore the effects of light regimes on the photosynthetic apparatus and thermal dissipation in A.villosum.During the study period, it was foggy or overcast from midnight till 11:30 a.m. of next day and clear later. The net photosynthetic rate(P n) of its sun leaves in the morning was similar to that in the afternoon (6.53 μmol·m -2·s -1),and was higher than the morning P n of shade leaves (5.94 μmol·m -2·s -1). In the afternoon, P n of shade leaves was similar to that of sun leaves, which was higher than P n of shade leaves in the morning.For both sun and shade plants, the apparent quantum yield was lower in the afternoon than in the morning. Minimal fluorescence(F o), maximal fluorescence(F m),maximal photochemical efficiency of PSⅡ(F v/F m),F m/F o, and potential efficiency of PSⅡ(F v/F o) decreased with the increase of light intensity, and reached the lowest values at about 15:00, then increased with the decrease of incident light intensity. This indicated that photo_inhibition of photosynthesis occurred already in the morning when the incident light intensity was lower than its light saturation point of photosynthesis, and was accelerated with increase of incident light intensity over the course of a day. Recovery from photo_inhibition started since 15:00 when incident light intensity started to decrease. On the contrary, non_photochemical quenching coefficient(q N) increased with the increase of incident light intensity,and maintained at the higher levels over the whole afternoon. This suggested that the xanthophyll cycle_dependent protective reaction accelerated gradually over the day. Photo_inhibition in sun leaves was more severe than in shade leaves. Shade treatment alleviated photo_inhibition. In contrast, q N was not significantly affected by light level and by shading treatment. In conclusion, photo_inhibition of photosynthesis occurred in leaves of A. villosum when light was much lower than the photosynthetic light saturation point. The photo_inhibition commonly occurred under different light environments. This was likely the result of xanthophyll cycle_dependent protective reaction, not due to photo_damage. Its xanthophyll cycle could start without excess light energy, and was not affected significantly by light treatment. A. villosum is able to adapt to strong light conditions due to its effective thermal dissipation mechanisms.