摘要
研究了大豆叶片逐步展开过程中的色素组成、气体交换、荧光动力学以及叶片角度等特性。随着叶片展开程度的增加 ,叶绿素含量和叶绿素 a/ b比值增加 ;光合速率 (Pn)也增加 ,揭示叶片展开过程中光合机构是逐步完善的。自然状态下 ,不同展开程度的叶片均未发生明显的光抑制 ;但将叶片平展并暴露在 12 0 0μmol/ (m2 · s)光下时幼叶发生严重的光抑制 ,伴随叶面积的增加光抑制程度减轻。强光下 ,尽管幼叶光呼吸 (Pr)的测定值较低 ,但幼叶光呼吸与总光合之比 (Pr/ Pm)较高。将叶片平展置于强光下时 ,幼叶的实际光化学效率 (ΦPSII)明显下调 ,非光化学猝灭 (NPQ)大幅增加 ;幼叶叶黄素库较大 ,光下积累较多的脱环氧化组分 ,揭示幼叶依赖叶黄素循环的热耗散增强。自然条件下测量叶片角度 ,观察到在叶片展开过程中叶柄夹角逐渐增加 ;日动态过程中幼叶的悬挂角随光强增加而明显减小 ,完全展开叶的悬挂角变化幅度很小。叶片角度的变化使实际照射到幼叶叶表的光强减少。推测较强的光呼吸。
Chloroplast pigments, gas exchange, chlorophyll a fluorescence kinetics and leaf orientation were extensively studied in soybean leaves from emergency to full expansion. During the development of soybean leaves, chlorophyll content, the ratio of Chl a/ Chl b and photosynthesis increased, indicating a gradual development of photosynthetic apparatus during leaf expansion. During daily courses, not only fully expanded leaves, but also young leaves were not seriously photoinhibited by strong irradiance under field condition. However, serious photoinhibition occurred in young leaves when vertically exposed to 1200 μmol/(m^2·s) irradiance, and the photoinhibition was alleviated with leaf expansion. It can be referred that there might be some regulative mechanisms behind these controversial phenomena. Under 1200 μmol/(m^2·s) irradiance, photorespiration (P_r) in young leaves measured by gas exchange were obviously low, whereas the ratio of photorespiration/mass photosynthesis (P_r/P_m) were distinctly enhanced, demonstrating that photorespiration might play a mild role against photoinhibition in young leaves. When leaves were placed in a horizontal position and vertically subjected to 1200 μmol/(m^2·s) irradiance, the actual photosystem II (PSII) efficiency (Φ_(PSII)) in young leaves were drastically down regulated, whereas, non-photochemical quenching (NPQ) were increased significantly. The significant down-regulation of Φ_(PSII) in young leaves under high irradiance was relieved gradually with leaf expanding, and NPQ declined during this process. Compared with the fully expanded leaves, young leaves, containing higher xanthophyll pool, exhibited a much higher level of zeaxanthin (Z) + antheraxanthin (A) to Chl when exposure to high irradiance. Remarkably, during the development of leaf, the petiole angle gradually increased over time. In addition, the midrib angle decreased with the increasing of irradiance during the diurnal courses in young leaves, whereas, in mature leaves no distinct changes was observed. These data indicated that the leaf orientation might reduce the irradiance reaching surface of young leaves under natural condition. Thus, we deduced that the co-operation of leaf angle, photorespiration and thermal dissipation depending on xanthophyll cycle under natural condition might alleviate the photoinhibion in young leaves.
出处
《生态学报》
CAS
CSCD
北大核心
2005年第2期319-325,共7页
Acta Ecologica Sinica
基金
中国科学院王宽诚博士后工作奖励基金资助项目
中国博士后科学基金资助项目~~
关键词
光合作用
叶绿素荧光
光抑制
叶黄素循环
光呼吸
叶角
photosynthesis
chlorophyll a fluorescence
photoinhibition
xanthophyll cycle
photorespiration
leaf orientation
