Optical sensors for fluorescence of chlorophyll a (f-Chl a) and phycocyanin (f-PC) are increasingly used as a proxy for biomass of algae and cyanobacteria, respectively. They provide measurements at high-frequency and modest cost. These sensors require site-specific calibration due to a range of interferences. Light intensity affects the fluorescence yield of cyanobacteria and algae through light harvesting regulation mechanisms, but is often neglected as a potential source of error for in-situ f-Chl a and f-PC measurements. We hypothesised that diel light variations would induce significant f-Chl a and f-PC suppression when compared to dark periods. We tested this hypothesis in a controlled experiment using three commercial fluorescence probes which continuously measured f-Chl a and f-PC from a culture of the cyanobacterium Dolichospermum variabilis as well as f-Chl a from a culture of the green alga Ankistrodesmus gracilis in a simulated natural light regime. Under light, all devices showed a significant (p<0.01) suppression of f-Chl a and f-PC compared to measurements in the dark. f-Chl a decreased by up to 79% and f-PC by up to 59% at maximum irradiance compared to dark-adapted periods. Suppression levels were higher during the second phase of the diel cycle (declining light), indicating that quenching is dependent on previous light exposure. Diel variations in light intensity must be considered as a significant source of bias for fluorescence probes used for algal monitoring. This is of high relevance as most monitoring activities take place during daytime and hence f-Chl a and f-PC are likely to be systematically underestimated under bright conditions. Compensation models, design modifications to fluorometers and sampling design are discussed as suitable alternatives to overcome light-induced fluorescence quenching.

用于叶绿素a（f-Chl a）和藻蓝蛋白（f-PC）荧光的光学传感器越来越多地分别用作藻类和蓝细菌生物量的代理。它们以高频率和适中的成本提供测量。由于一系列干扰，这些传感器需要进行特定于现场的校准。光强通过光收集调节机制影响蓝藻和藻类的荧光产量，但通常被忽略为原位f-Chl a和f-PC测量的潜在误差来源。我们假设diel光的变化会诱导明显的f-Chl a与黑暗时段相比，f-PC抑制效果更好。我们测试了使用三个商业荧光探针以受控的实验这一假设其中连续测量的f-叶绿素一个和f-PC从蓝藻的培养Dolichospermum变异以及F-叶绿素一个从绿色的培养藻类Ankistrodesmus眼虫在模拟的自然光体制。下光，所有的设备表现出显著（p F-叶绿素<0.01）抑制一个和f-PC相比在黑暗中测量。f-Chl a与暗适应期相比，在最大辐照度下，f-PC降低了79％，f-PC降低了59％。在diel循环的第二阶段（光线下降），抑制水平较高，这表明淬灭取决于先前的曝光。必须将光强度的Diel变化视为用于藻类监测的荧光探针的重要偏差来源。由于大多数监测活动都在白天进行，因此这具有很高的相关性，因此在明亮的条件下可能会低估f-Chl a和f-PC的含量。讨论了补偿模型，荧光计的设计修改和采样设计，作为克服光诱导的荧光猝灭的合适替代方法。