墨兰对氮营养和波动光强复合胁迫的光合调控响应

Photosynthetic regulation of Cymbidium sinense in response to combined stress of nitrogen and fluctuating light intensity

关键词:  墨兰, 氮, 波动光, 光系统I, 光系统Ⅱ, 环式电子传递

Key words:  Cymbidium sinense, nitrogen, fluctuating light, PS I, PS Ⅱ, cyclic electron flow

摘要:

墨兰(Cymbidium sinense)是我国的传统名花,具有悠久的栽培历史,该物种为林下荫生植物,生境破坏和森林冠层结构的改变都会导致其遭受氮素和光照波动的双重影响。为了探究墨兰的光合作用响应这种复合胁迫的机制,该文研究了不同氮浓度处理下墨兰叶片的氮含量、叶绿素含量、光系统I(PS I)和光系统Ⅱ(PS Ⅱ)对波动光强的影响。结果表明:(1)0 mmol·L^-1氮处理下,墨兰叶片的氮含量、叶绿素含量、PS Ⅱ最大量子效率(F_v/F_m)和PS I最大可氧化的P700信号(P_m)降低,而非光化学猝灭和PS Ⅱ非调节性能量耗散被大量激发。(2)1.25、5、10 mmol·L^-1氮处理下,光强突然增加使墨兰叶片的PS I反应中心表现为先过度还原,随后过度还原态被逐渐解除; 环式电子传递的激发表现为先增加后逐渐下降,说明环式电子传递的动态调节和PS I的氧化还原态密切相关。(3)波动光下,0 mmol·L^-1氮处理的墨兰叶片没有表现出PS I的过度还原,主要是因为其PS Ⅱ释放的电子很少,避免了过量电子被传递到PS I。综上认为,氮素的波动会显著影响墨兰对波动光强的光合生理响应,这为墨兰的人工栽培和保护提供了科学依据,并有助于探究林下植物光合作用响应氮素和波动光复合胁迫的机制。

Abstract:

Cymbidium sinense is a well-known traditional orchid in China, and has been widely cultivated for a long time. This species is typically a shade species under the forest, but habitat destruction and tree canopy structure change make it subject to the dual fluctuation of light and nutrients. To explore the photosynthetic response of C. sinense to the combined stress of nitrogen and fluctuating light intensity, the leaf nitrogen content, chlorophyll content, and the responses of photosystem I(PS I)and photosystem Ⅱ(PS Ⅱ)to fluctuating light intensity were investigated under different nitrogen treatments. The results were as follows:(1)The C. sinense under 0 mmol·L^-1 nitrogen treatment had lower values for leaf nitrogen content, chlorophyll content, PS Ⅱ maximum quantum efficiency(F_v/F_m)and the value of maximum oxidizable P700 of PS I(P_m), but motivated a large amount of non-photochemical quenching and PS Ⅱ non-regulatory energy dissipation.(2)When the light intensity suddenly increased, the PS I reaction center showed over-reduction firstly, and then the over-reduction state was gradually released under 1.25 mmol·L^-1, 5 mmol·L^-1 and 10 mmol·L^-1 nitrogen treatments. Meanwhile, the excitation degree of cyclic electron flow increased first and then gradually decreased, indicating that the dynamic adjustment of cyclic electron flow was closely linked to the redox state of PS I.(3)Under fluctuating light intensity, the excessive reduction of PS I was not observed in C. sinense under 0 mmol·L^-1 nitrogen treatment. This was mainly because the few electrons were released by PS Ⅱ, thus avoiding the transfer of excess electrons to PS I. These results suggest that nitrogen fluctuation can affect significantly the response of C. sinense to fluctuating light intensity. These findings provide a scientific basis for the cultivation and conservation of C. sinense, and are helpful to explore how photosynthesis of shade plant responds to the combined stress of nitrogen and fluctuating light intensity.