热带雨林冠层树种绒毛番龙眼两种发育阶段叶片的光抑制

PHOTOINHIBITION OF PHOTOSYNTHESIS IN LEAVES OF TWO DEVELOPING STAGES OF A TROPICAL RAINFOREST CANOPY TREE, POMETIA TOMENTOSA

通过测定西双版纳热带雨林冠层树种绒毛番龙眼 (Pometiatomentosa)完全伸展嫩叶和成熟叶的叶片解剖、生理特征和雨季晴天自然条件下叶绿素a荧光以及午间强光对部分保护酶活性和膜脂过氧化作用的影响 ,探讨了两种不同发育阶段叶片光合作用的光抑制与强光和温度的关系。结果表明 :绒毛番龙眼全展嫩叶和成熟叶表现出明显的解剖和生理特征差异。与全展嫩叶相比 ,成熟叶的叶片较厚、叶绿素含量高、气孔导度大、羧化效率高、最大净光合速率和光饱和点高 ,而气孔密度和保卫细胞长度没有显著差别。在雨季晴天自然条件下 ,午间最高光强可达 2 2 0 0 μmol·m-2 ·s-1 以上 ,最高叶温比气温高 7～ 8℃ ,而成熟叶片的最高温度比全展嫩叶高 1 .5～ 2℃。上午随光强的增大 ,两种叶片的非光化学猝灭系数 (NPQ)增大 ,PSⅡ原初光化学效率 (Fv Fm)、实际光化学效率 [(Fm′_Fs) Fm′]逐渐减小 ,在 1 5∶30左右达最小。下午随着光强的减弱 ,Fv Fm逐渐恢复 ,在傍晚基本恢复到清晨值。初始荧光 (F0 )在一天中变化很小。这表明绒毛番龙眼叶片光抑制是非辐射能量耗散增加引起的保护光合机构免受光破坏的保护性反应 ,而非光破坏。全展嫩叶比成熟叶有较低的光化学效率和非辐射耗散能力 ,对强光和高温处理的敏感性也较强 ,但在自?

Pometia tomentosa, is a dominant uppermost canop y tree and a symbol species of vallyland forest in Xishuangbanna tropical rainfo rest. In addition to anatomical and physiological characteristics, diurnal c hanges in chlorophyll fluorescence parameters were measured with a modulated chl orophyll fluorescence monitoring system (FMS2) in order to explore the differenc e of diurnal photoinhibition in leaves of two developing stages, young fully exp anded leaves and mature leaves of Pometia tomentosa in the rainy season. Th e di fference in the effect of midday strong light and high temperature on the activi ties of partly protective enzymes was also briefly analyzed. The results showed : leaf thickness, chlorophyll contents, stomatal conductance, carboxylation effi ciency, maximum net photosynthetic rate and light saturation point of mature lea ves were much higher than those of young fully expanded leaves, while the stomat al density and guard cell length were similar between two leaves. On clear days in the rainy season, the highest photon flux density can exceed 2 200 μmol·m -2 ·s -1 , the highest leaf temperature was 7_8 ℃ higher than air temp erature, and the highest leaf temperature of mature leaves was 1.5_2 ℃ higher than that of young fully expanded leaves. Non_photochemical quenching (NPQ) was increased, the initial photochemical efficiency (Fv/Fm) and actual photo chemical efficiency [(Fm′_Fs)/Fm] decreased gradually in the morning, and reached the lowest values at about 15∶30. The reverse changes occurred in the afternoon, at dusk these parameters could recover to nearly the original daw n level. The decrease in Fv/Fm was mainly caused by a decrease in Fm, be cause initial fluorescence (F 0) did not change significantly over the cou rse of the day. This suggested that the photoinhibition observ ed in Pometia tomentosa was due to photoprotective process and not to ph otoi nhibitory damage. The initial photochemical efficiency (Fv/Fm) of young full y ex panded leaves was lower than that of mature leaves, and exhibited more sensitive t o strong light and high temperature treatment, but their diurnal photoinhibition was statistically similar in the field. After field strong light at midday the protective enzymes (SOD, APX) increased, while H 2O 2 content was stable and t he l ipid peroxide level was lower in young expanded leaves compared with mature leav es. We concluded that the alleviated photoinhibition in young expanded leaves mi ght be caused by its lower photochemical efficiency and leaf temperature, as wel l as active protection by higher activities of protective enzymes under the fi eld conditions.