Does pigment composition reflect phytoplankton community structure in differing temperature and light conditions in a deep alpine lake? An approach using HPLC and delayed fluorescence techniques

• Published in: Journal of phycology Vol. 43; no. 6; pp. 1108 - 1119
• Main Authors: Greisberger, Sonja, Teubner, Katrin
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford, UK : Blackwell Publishing Ltd 01.12.2007; Blackwell Publishing Ltd
• Subjects: Bacillariophyceae; Bacillariophyta; Cryptophyta; cryptophytes; Cyanobacteria; diatoms; Freshwater; marker pigment ratios; metalimnion; oscillaxanthin; Austria, Oberoesterreich, Mondsee L; Austria
• ISSN: 0022-3646; 1529-8817
• DOI: 10.1111/j.1529-8817.2007.00404.x

In vivo delayed fluorescence (DF) and HPLC/CHEMTAX pigment analyses were used to investigate seasonal and depth distributions of phytoplankton in a deep alpine mesotrophic lake, Mondsee (Austria). Using chl a equivalents, we determined significant relationships with both approaches. Community structure derived from pigment ratios of homogenous samples was compared with microscopic estimations using biovolume conversion factors. An advantage of the HPLC/CHEMTAX method was that it gave good discrimination among phytoplankton groups when based on a pigment ratio matrix derived from multiple regression analysis. When a single algal group was dominant, such as epilimnetic diatoms or hypolimnetic cyanobacteria in the deep chl maxima, HPLC/CHEMTAX results were significantly correlated with microscopic estimations (diatoms: r = 0.93; cyanobacteria: r = 0.94). Changes in the composition of photosynthetically active pigments were investigated with DF and benefited from excitation spectra that considered all light-harvesting pigments, which made it possible to assess the enhancement of accessory photosynthetically active pigments relative to active chl a (chl aDF₆₇₂). Changes in similarity index, based on normalized DF spectra, confirmed compositional shifts observed by microscopy. At chosen wavelengths of DF spectra, 534 and 586 nm, we generally observed a significantly inverse relationship between normalized DF intensities and temperature and light along both seasonal and depth gradients. The relative increase in photosynthetically active pigments other than chl aDF₆₇₂ under low light and temperature was caused by an increasing dominance of diatoms and/or phycobilin-rich cyanobacteria and Cryptophyta. DF spectra provided a more accurate picture of community pigments acclimated to light and temperature conditions than the β-carotene:chl a ratio derived from HPLC.