Abstract
Photo-physiological variability of in vivo chlorophyll fluorescence (CF) per unit of chlorophyll concentration (CC) is analyzed using a biophysical model to improve the accuracy of CC assessments. Field measurements of CF and photosystem II (PSII) photochemical yield (PY) with the Advanced Laser Fluorometer (ALF) in the Delaware and Chesapeake Bays are analyzed vs. high-performance liquid chromatography (HPLC) CC retrievals. It is shown that isolation from ambient light, PSII saturating excitation, optimized phytoplankton exposure to excitation, and phytoplankton dark adaptation may provide accurate in vivo CC fluorescence measurements (R2 = 0.90-0.95 vs. HPLC retrievals). For in situ or flow-through measurements that do not allow for dark adaptation, concurrent PY measurements can be used to adjust for CF non-photochemical quenching (NPQ) and improve the accuracy of CC fluorescence assessments. Field evaluation has shown the NPQ-invariance of CF/PY and CF(PY-1-1) parameters and their high correlation with HPLC CC retrievals (R2 = 0.74-0.96), while the NPQ-affected CF measurements correlated poorly with CC (R2 = -0.22).
Highlights
Chlorophyll a (Chl) is a photosynthetic pigment that plays a key role in photosynthesis [1]
The conversion equation CC = 4.40CFU was derived from the correlation (R2 = 0.93) between CC retrievals with high performance liquid chromatography (HPLC) and the Advanced Laser Fluorometer (ALF) chlorophyll fluorescence (CF) measurements of the darkadapted water samples representing diverse coastal and estuarine waters (Fig. 7A in [12])
As evident from comparison with the high-performance liquid chromatography (HPLC) CC measurements in water samples collected along the transect, the ALF CC assessments based on the nighttime or lowlight measurements were in good agreement with the respective HPLC measurements
Summary
Chlorophyll a (Chl) is a photosynthetic pigment that plays a key role in photosynthesis [1]. CF measurements can provide information about CC, phytoplankton community structure [11,12,13,14,15,16], physiological status, photosynthetic efficiency and productivity [17,18,19,20,21,22,23,24,25,26,27,28]. The relationship between CF and CC depends on phytoplankton taxonomy, cell size, organization of photosynthetic apparatus and physiological status. Some fluorometers [12, 17, 21, 22, 37, 38] provide measurements of physiological parameters that potentially can be used to adjust CF magnitudes affected by photo-physiological variability
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