Lichtenberg Mads, Larkum Anthony W D, Kühl Michael
Marine Biological Section, Department of Biology, University of Copenhagen Helsingør, Denmark.
Plant Functional Biology and Climate Change Cluster (C3), University of Technology Sydney Sydney, NSW, Australia.
Front Microbiol. 2016 Feb 26;7:230. doi: 10.3389/fmicb.2016.00230. eCollection 2016.
Coral photophysiology has been studied intensively from the colony scale down to the scale of single fluorescent pigment granules as light is one of the key determinants for coral health. We studied the photophysiology of the oral and aboral symbiont band of scleractinian coral Montastrea curta to investigate if different acclimation to light exist in hospite on a polyp scale. By combined use of electrochemical and fiber-optic microsensors for O2, scalar irradiance and variable chlorophyll fluorescence, we could characterize the physical and chemical microenvironment experienced by the symbionts and, for the first time, estimate effective quantum yields of PSII photochemistry and rates of electron transport at the position of the zooxanthellae corrected for the in-tissue gradient of scalar irradiance. The oral- and aboral Symbiodinium layers received ∼71% and ∼33% of surface scalar irradiance, respectively, and the two symbiont layers experience considerable differences in light exposure. Rates of gross photosynthesis did not differ markedly between the oral- and aboral layer and curves of PSII electron transport rates corrected for scalar irradiance in hospite, showed that the light use efficiency under sub-saturating light conditions were similar between the two layers. However, the aboral Symbiodinium band did not experience photosynthetic saturation, even at the highest investigated irradiance where the oral layer was clearly saturated. We thus found a different light acclimation response for the oral and aboral symbiont bands in hospite, and discuss whether such response could be shaped by spectral shifts caused by tissue gradients of scalar irradiance. Based on our experimental finding, combined with previous knowledge, we present a conceptual model on the photophysiology of Symbiodinium residing inside living coral tissue under natural gradients of light and chemical parameters.
由于光照是影响珊瑚健康的关键因素之一，因此从群体尺度到单个荧光色素颗粒尺度，人们对珊瑚的光生理学进行了深入研究。我们研究了石珊瑚短星珊瑚口面和反口面共生体带的光生理学，以调查在珊瑚虫尺度上，共生体在宿主体内是否存在不同的光适应情况。通过联合使用电化学和光纤微传感器来测量氧气、标量辐照度和可变叶绿素荧光，我们能够表征共生体所经历的物理和化学微环境，并首次估算了PSII光化学的有效量子产率以及在考虑标量辐照度组织内梯度校正后虫黄藻位置处的电子传输速率。口面和反口面的共生藻层分别接收了约71%和33%的表面标量辐照度，并且这两个共生藻层在光照暴露方面存在显著差异。口面和反口面层的总光合作用速率没有明显差异，在宿主体内对标量辐照度校正后的PSII电子传输速率曲线表明，在亚饱和光照条件下，两层的光利用效率相似。然而，即使在最高的研究辐照度下，口面层明显饱和，反口面的共生藻带也未达到光合饱和。因此，我们发现了宿主体内口面和反口面共生体带不同的光适应反应，并讨论了这种反应是否可能由标量辐照度的组织梯度引起的光谱变化所塑造。基于我们的实验结果，并结合先前的知识，我们提出了一个关于在自然光照和化学参数梯度下，生活在活珊瑚组织内的共生藻光生理学的概念模型。
