Effects of shading on photosynthetic characteristics and chlorophyll fluorescence parameters in leaves of Hydrangea macrophylla
CAIJian-Guo*, WEIMeng-Qi, ZHANGYi, WEIYun-Long School of Landscape Architecture, Zhejiang Agriculture and Forestry University, Lin’an, Zhejiang 311300, China 版权声明:2017植物生态学报编辑部本文是遵循CCAL协议的开放存取期刊,引用请务必标明出处。 基金资助:基金项目 国家自然科学基金(31272494)、浙江省教改课题(KC14015和KC14032)、浙江省花卉团队项目(2011R50034-02)和浙江省林学重中之重一级学科研究生科研创新项目(201531)
关键词:绣球;遮阴;光合作用;叶绿素荧光;光适应 Abstract 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 macrophylla to changes in light regimes in view of the distribution of energy absorbed and photosynthetic characteristics.Methods Three light regimes including natural and shade (shading rate 50% and 75% of natural light) were applied to plants for 60 days. After the treatment, the gas-exchange, chlorophyll a fluorescence and photosynthesis-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 stress, 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 distribution in photosystem II (PSII) in the leaves of Hydrangea macrophylla. In general, the 70% of incident light in photochemical energy utilization was distributed to thermal dissipation, 20% was distributed to non-regulated energy 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.
由表2可知, 50%遮光率处理下的绣球叶片的Pn和Tr分别高于全光照和75%遮光率处理, 而Ci和WUE低于全光照。50%遮光率处理叶的Pn、Ci、Tr和WUE与全光照叶差异显著, 其Gs与后者差异不显著。说明Pn与Tr的变化一致, 遮阴增加了叶片的Pn, 较高的Pn伴随着较高的Tr。50%遮光处理后, 叶片Gs没有发生变化, 但是WUE降低了18.18%, 说明遮阴下的叶片需要消耗更多的水分以维持其高的净光合效率, 而Ci降低说明叶片固定C的能力提高。75%遮光率下的Gs与50%遮光率和全光照下的差异显著, 下降了50%, 说明过度遮阴影响绣球叶片气体交换能力, 从而引起叶片的Pn下降。由此得出, 绣球在适度遮阴后, 叶片会通过增加Tr和提高CO2同化力来提高Pn, 但过度遮阴会使叶片Pn下降, 原因是Gs降低使得叶片气体交换能力下降。 Table 2 表2 表2不同遮光率处理对叶片气体交换参数影响(平均值±标准偏差) Table 2Effects of light treatments on the gas exchange parameters of Hydrangea macrophylla (mean ± SD)
处理 Treatment
参数 Parameter
Pn (μmol CO2·m-2·s-1)
Ci ( μmol·mol-1)
Gs (mol·m-2·s-1)
Tr (mmol·m-2·s-1)
WUE (mmol CO2·mol-1H2O)
全光 Full light
1.64 ± 0.34a
326.55 ± 21.45a
0.04 ± 0.004b
0.92 ± 0.11a
1.82 ± 0.53a
遮光率50% Shading rate 50%
2.14 ± 0.38b
300.46 ± 17.85b
0.04 ± 0.009b
1.40 ± 0.22b
1.54 ± 0.27b
遮光率75% Shading rate 75%
1.73 ± 0.28a
293.99 ± 18.33b
0.02 ± .009a
0.86 ± 0.26a
2.11 ± 0.47a
Ci, intercellular CO2 content; Gs, stomatal conductance; Pn, net photosynthetic rate; Tr, transpiration rate; WUE, water use efficiency. Different letters in same column indicate significant differences between treatments (p < 0.05).Ci, 胞间CO2浓度; Gs, 气孔导度; Pn, 净光合速率; Tr, 蒸腾速率; WUE, 水分利用效率。同列不同字母表示处理间差异显著(p < 0.05)。 新窗口打开
2.3 遮阴对叶绿素荧光参数的影响
叶绿素荧光是光合作用的探针, 通过荧光参数分析可以了解光合机构内部一系列重要的调节过程, Fv/Fm是PSII光能转化率的指标(缴丽莉等, 2007)。由表3看出, 遮阴导致Fv/Fm增加, 3种光照处理间差异显著, 全光照下Fv/Fm低于50%遮光率处理, Fo高于50%遮光率处理, 根据张守仁(1999)的观点, Fo是判断PSII反应中心运转情况的重要指标, Fo上升表明PSII反应中心受到破坏或失活, Fv/Fm下降是光抑制的重要特征, 因此推测全光照下的绣球叶片发生了光抑制。NPQ的变化反映了非光化学耗散的能量, 其中包括了类囊体膜耗散热能, 是植物光合机构的自我保护机制(何炎红等, 2006)。随着生长光照的减弱, NPQ值在降低, 说明遮光处理降低了PSII天线色素吸收光能以热的形式耗散的比例, 提高了PSII吸收光能的利用效率。 Table 3 表3 表3不同遮阴处理对叶绿素荧光参数比较(平均值±标准偏差) Table 3Effects of light treatments on chlorophyll a fluorescence parameters of Hydrangea macrophylla (mean ± SD)
参数 Parameter
处理 Treatment
全光 Full light
遮光率50% Shading rate 50%
遮光率75% Shading rate 75%
PSⅡ原初光能转化效率 Fv/Fm
0.63 ± 0.03b
0.67 ± 0.01c
0.60 ± 0.04a
PSⅡ潜在活性 Fv/Fo
1.72 ± 0.21b
2.00 ± 0.08c
1.51 ± 0.20a
初始荧光 Fo
786.59 ± 13.23b
770.21 ± 21.12a
836.86 ± 28.73b
PSII实际光量子产量 F°v/F°m
0.25 ± 0.01a
0.26 ± .04a
0.28 ± 0.06a
非光化学淬灭系数 NPQ
2.39 ± 0.16c
1.95 ± 0.09b
1.41 ± 0.34a
光化学淬灭系数 qP
0.17 ± 0.04a
0.18 ± 0.02a
0.15 ± 0.03a
电子传递速率 ETR
19.43 ± 3.88a
20.31 ± 5.53a
18.57 ± 4.50a
ETR, electron transport rate; Fo, initial fluorescence intensity; Fv/Fm, maximal quantum efficiency of PSII; Fv/Fo, potential efficiency of primary conversion of light energy of PSII; F°v/F°m, actual photochemical efficiency of PSII; NPQ, non-photochemical quenching; qP, photochemical quenching. 新窗口打开
2.4 叶片吸收光能的分配
植物叶片吸收的光能可分为3部分: 一是天线热耗散的能量(D), 二是用于光化学反应的部分(P), 三是反应中心有非光化学反应耗散的能量(E) (Depuydt et al., 2009)。分析吸收光能的分配将有利于了解植物叶片对吸收光能的分配策略(胡文海等, 2015)。由表4可知, P表现为: 50%遮光率 > 全光照> 75%遮光率。E表现为: 75%遮光率 > 50%遮光率 > 全光照。D表现为: 全光照和遮光率75%的D值高于遮光率50%, 由此看出, 遮光率50%的绣球把吸收的光能较多的分配于光化学反应部分, 而用于天线热耗散的能量较少。说明在此处理下, 绣球叶片的光化学反应能量利用率最大, 这与NQP变化一致。遮光率75%条件下, 绣球由于光照不足, 叶片吸收的光能用于参与光化学反应耗散的份额降低。而较高的E值表明PSII光化学反应和保护性调节机制没有发挥作用, 积累了大量的激发能, 这有可能会对PSII反应中心产生破坏作用。全光照下, 绣球叶片D值较高, 说明叶片此时具有较高的可调控生理代谢, 能够将过剩的光能较多地分配给热耗散途径。而热耗散比率的增加也反映了此时光能捕获效率降低, 推测植物有可能处于光抑制状态下(黄秋娴等, 2015)。因此, 绣球处于饱和光环境时, 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, 绣球的主要光保护机制为PSII天线色素吸收光能通过热的形式耗散, 以此削弱反应中心过量的激发能。 Table 4 表4 表4叶片吸收光能的分配 Table 4The distribution of light energy absorbed in Hydrangea macrophylla under different light intensities
处理 Treatment
能量分配 Energy distribution
天线热耗散 Fraction of photons dissipated in the antenna (%)
光化学反应耗散 Fraction of photons utilized in PSII photochemistry (%)
非光化学反应耗散 Fraction of absorbed photons by PSII neither used in photochemistry nor dissipated in the PSII (%)
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