Department of Biology, University of Waterloo, Waterloo, Ontario, Canada.
Department of Biology, University of Waterloo, Waterloo, Ontario, Canada.
J Photochem Photobiol B. 2018 Dec;189:36-48. doi: 10.1016/j.jphotobiol.2018.09.013. Epub 2018 Sep 20.
Multi-wavelength fluorometers, such as the bbe FluoroProbe (FP), measure excitation spectra of chlorophyll a (Chl-a) fluorescence to infer the abundance and composition of phytoplankton communities as well as the concentration of chromophoric dissolved organic matter (CDOM). Experiments were conducted on laboratory cultures and on natural communities of freshwater phytoplankton to determine how the response of phytoplankton to high irradiance might affect fluorometric estimates of community composition and concentrations of Chl-a and CDOM. Cultures of a representative cyanobacterium, bacillariophyte, synurophyte, cryptophyte, and chlorophyte revealed changes in Chl-a excitation spectra as irradiance was increased to saturating levels and non-photochemical quenching (NPQ) increased. The degree of change and resulting classification error varied among taxa, being strong for the synurophyte and cryptophyte but minimal for the cyanobacterium. Acute-exposure experiments on phytoplankton communities of varying taxonomic composition from five lakes yielded variable results on apparent community composition. There was a consistent decrease in CDOM estimates, whereas Chl-a estimates were generally increased. Subsequent exposure to low PAR relaxed NPQ and tended to reverse the effects of high irradiance on composition, total Chl-a, and CDOM estimates. Relaxation experiments on near-surface communities in a sixth, large lake, Georgian Bay, showed that total Chl-a estimates increased by 44% on average when dark treatments were used to relax NPQ, though, in contrast to the findings from the small lakes, there was little effect on CDOM estimates. We observed a statistically-significant, negative linear relationship between the photon flux density of in situ irradiance and the accuracy of taxonomic assignment by FP in Georgian Bay. Not discounting the correlations between light intensity and the accuracy of the FP that were observed in this study, we conclude that the applicability of the reference spectra to the system under investigation is a more important consideration than variability in natural irradiance conditions.
多波长荧光计，如 bbe FluoroProbe（FP），测量叶绿素 a（Chl-a）荧光的激发光谱，以推断浮游植物群落的丰度和组成以及有色溶解有机物（CDOM）的浓度。该实验在实验室培养物和天然淡水浮游植物群落中进行，以确定浮游植物对高光强的反应如何影响群落组成和 Chl-a 与 CDOM 浓度的荧光估计。对代表性蓝藻、甲藻、金藻、隐藻和绿藻的培养物进行了实验，结果表明，随着辐照度增加到饱和水平和非光化学猝灭（NPQ）增加，Chl-a 激发光谱发生变化。变化的程度和由此产生的分类错误在分类群之间有所不同，对于金藻和隐藻来说变化很大，但对于蓝藻来说则最小。对来自五个湖泊的具有不同分类组成的浮游植物群落进行的急性暴露实验，对表观群落组成的结果存在差异。CDOM 估计值持续下降，而 Chl-a 估计值通常增加。随后暴露于低 PAR 会放松 NPQ，并倾向于逆转高光强对组成、总 Chl-a 和 CDOM 估计值的影响。在第六个大湖 Georgian Bay 的近表面群落中进行的松弛实验表明，当使用黑暗处理来松弛 NPQ 时，总 Chl-a 估计值平均增加了 44%，与小湖泊的结果相反，CDOM 估计值几乎没有影响。我们观察到 Georgian Bay 中现场辐照度的光量子通量密度与 FP 进行分类分配的准确性之间存在统计学上显著的负线性关系。我们不排除在这项研究中观察到的光强与 FP 准确性之间的相关性，但我们得出的结论是，参考光谱与所研究系统的适用性比自然辐照度条件的可变性更为重要。
