遮阴对绣球光合特性和叶绿素荧光参数的影响

Effects of shading on photosynthetic characteristics and chlorophyll fluorescence parameters in leaves of Hydrangea macrophylla

为了从光合作用机制及叶片吸收光能分配的角度解释绣球(Hydrangea macrophylla)对不同光环境的适应机制,探讨绣球对光环境变化的生理响应和适应性,该文以盆栽的绣球品种‘无尽夏新娘’为材料,设置遮阴(遮光率为50%、75%)两种处理,并以全光照为对照,经过60天的处理,测定其光合-光响应曲线、气体交换参数、叶绿素荧光参数。结果表明:遮阴60天后,绣球的暗呼吸速率、光补偿点和光饱和点均有所下降,而表观量子效率(AQY)上升,说明绣球能够通过这些途径提高对弱光的利用能力并降低呼吸消耗,以维持植株正常生长,从而表现出了极强的适应能力;在50%的遮阴处理下,绣球叶片的净光合速率、胞间CO2浓度、蒸腾速率和水分利用效率均与其全光照和75%遮阴处理下差异显著;遮阴导致光系统II(PSII)最大光化学效率(Fv/Fm)增加,3种光照处理下呈显著差异,全光照下Fv/Fm低于50%遮阴处理,初始荧光水平高于50%遮阴处理,推断此条件下的绣球叶片发生了光抑制;而随着光照的减弱,非光化学淬灭系数在降低,说明遮阴降低了绣球叶片PSII天线色素吸收光能以热的形式耗散的比例,绣球叶片吸收的能量约70%用于热耗散,约20%用于非光化学反应,仅有4%的能量用于光化学反应,说明绣球处于饱和光环境下时,主要通过提高叶片吸收光能向热耗散等PSII调节性能量耗散途径的分配,削弱反应中心过量激发能的积累。

Aims The objectives were to investigate the effects of different light intensities on photosynthetic characteristics and chlorophyll fluorescence parameters, to clarify the physiological responses and photo-protective mechanisms of Hydrangea maerophylla to changes in light regimes in view of the distribution of energy absorbed and photo- synthetic characteristics. Methods Three light regimes including natural and shade （shading rate 50% and 75% of natural light） were ap- plied to plants for 60 days. After the treatment, the gas-exchange, chlorophyll a fluorescence and photosynthe- sis-light curves were measured by a portable leaf gas exchange system （LI-6400）. Important findings The results showed that the weak light intensity treatment reduced dark respiration rate, light compensation point and light saturation point of plant, but increased apparent quantum yield, suggesting that plants had the physiological strategy to utilize the weakening light by reducing respiration. The net photosynthetic rate, intercellular CO2 concentration, transpiration rate and water use efficiency of plants grown below 50% of natural light showed significant difference compared with natural and shading rate 75% of natural light. There were significant difference between natural and shade treatments in the maximal quantum efficiency of PSII （Fv/Fm）, as indicated that it was significantly less at full light than that at 50% of natural light. Initial fluorescence intensity （Fo） of plants was higher at full light than that at 50% of natural light, suggesting that photoinhibition occurred in natural light. The non-photochemical quenching （NQP） decreased with the aggravation of shade str- ess, indicating that shading decreased the efficiency of photochemical reaction by reducing the fraction of incident light in photochemical energy utilization and decreased thermal dissipation through regulating energy distribu- tion in photosystem II （PSII） in the leaves of Hydrangea maerophylla. In general, the 70% of incident light in photochemical energy utilization was distributed to thermal dissipation, 20% was distributed to non-regulated en- ergy dissipation and 4% was distributed to effective photochemical reaction. In conclusion, responses of plants to increased irradiance are governed by strategy： to utilize a high fraction of incident light in photochemistry and regulate energy dissipation in PSII and weaken the accumulation of excess excitation energy in PSII to protect the photosynthetic apparatus in the leaves of H, macrophylla under saturated radiation.