Kühl M, Fenchel T
Marine Biological Laboratory, University of Copenhagen, Strandpromenaden 5, DK-3000 Helsingør, Denmark
Microb Ecol. 2000 Aug;40(2):94-103. doi: 10.1007/s002480000061.
Zonations of photosynthesis and photopigments in artificial cyanobacterial mats were studied with (i) oxygen and pH microsensors, (ii) fiber-optic microprobes for field radiance, scalar irradiance, and PSII fluorescence, and (iii) a light microscope equipped with a spectrometer for spectral absorbance and fluorescence measurements. Our analysis revealed the presence of several distinct 1-2 mm thick cyanobacterial layers mixed with patches of anoxygenic photosynthetic bacteria. Strong attenuation of visible light confined the euphotic zone to the uppermost 3 mm of the mat, where oxygen levels of 3-4 times air saturation and a pH peak of up to pH 8.8 were observed under saturating irradiance (413 µmol photon m(-2) s(-1)). Oxygen penetration was 5 mm in light and decreased to 1 mm in darkness. Volumetric oxygen consumption in the photic and aphotic zones of illuminated mat was 5.5 and 2.9 times higher, respectively, than oxygen consumption in dark incubated mats. Scalar irradiance reached 100-150% of incident irradiance in the upper 0.5 mm of the mat due to intense scattering in the matrix of cells, exopolymers, and carbonate precipitates. In deeper mat layers scalar irradiance decreased nearly exponentially, and highest attenuation coefficients of 6-7 mm(-1) were found in cyanobacterial layers, where photosynthesis and photopigment fluorescence also peaked. Visible light was attenuated >100 times more strongly than near infrared light. Microscope spectrometry on thin sections of mats allowed detailed spectral absorbance and fluorescence measurements at defined positions relative to the mat surface. Besides strong spectral signals of cyanobacterial photopigments (Chl a and phycobiliproteins), the presence of both green and purple photosynthetic bacteria was evident from spectral signals of Bchl a and Bchl c. Microprofiles of photopigment absorbance correlated well with microdistributions of phototrophs determined in an accompanying study.
（i）氧和pH微传感器；（ii）用于测量场辐射、标量辐照度和PSII荧光的光纤微探针；（iii）配备有用于光谱吸光度和荧光测量的光谱仪的光学显微镜。我们的分析揭示了存在几个明显的、厚度为1-2毫米的蓝藻层，这些蓝藻层与无氧光合细菌斑块混合在一起。可见光的强烈衰减将光合有效辐射层限制在席的最上层3毫米处，在饱和辐照度（413微摩尔光子·米-2·秒-1）下，此处观察到氧含量达到空气饱和度的3-4倍，pH峰值高达pH 8.8。光照下氧的渗透深度为5毫米，黑暗中降至1毫米。光照席的光合层和无光层的体积氧消耗量分别比黑暗培养席中的氧消耗量高5.5倍和2.9倍。由于细胞、胞外聚合物和碳酸盐沉淀物基质中的强烈散射，标量辐照度在席的上0.5毫米处达到入射辐照度的100-150%。在更深的席层中，标量辐照度几乎呈指数下降，在蓝藻层中发现了最高衰减系数为6-7毫米-1，光合作用和光合色素荧光也在此处达到峰值。可见光的衰减比近红外光强烈100倍以上。对席薄片的显微镜光谱分析允许在相对于席表面的特定位置进行详细的光谱吸光度和荧光测量。除了蓝藻光合色素（叶绿素a和藻胆蛋白）的强光谱信号外，从细菌叶绿素a和细菌叶绿素c的光谱信号中明显可以看出绿色和紫色光合细菌的存在。光合色素吸光度的微剖面与在一项伴随研究中确定的光合生物的微分布密切相关。
