Dark adaptation and ability of pulse-amplitude modulated (PAM) fluorometry to identify nutrient limitation in the bloom-forming cyanobacterium, Microcystis aeruginosa (Kützing)

Harmful algal blooms in inland waters are widely linked to excess phosphorus (P) loading, but increasing evidence shows that their growth and formation can also be influenced by nitrogen (N) iron (Fe). Deficiency N, P, Fe differentially affects cellular photosystems is manifested as changes photosynthetic yield (Fv/Fm). While Fv/Fm has been increasingly used a rapid convenient situ gauge of nutrient deficiency, there few rigorous comparisons instrument sensitivity ability resolve specific stresses. This study evaluated the application cyanobacteria using controlled experiments on single isolate tested three hypotheses: i) measurements taken with different PAM fluorometers distinguish among limitation nutrients, ii) made addition DCMU comparable fluorometers, iii) dark adaptation not necessary for reliable measurements. We compared from bloom-forming Microcystis aeruginosa (UTEX LB 3037) grown nutrient-replete treatment (R) N-, P-, Fe-limited treatments (LN, LP, LFe, respectively), pulse-amplitude modulated (PAM) chemical photosynthesis inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), effects prior measurement. There were significant differences estimates light- versus dark-adapted cell suspensions over whole experiment (21 days), which all significantly higher than DCMU-based However, had no effect when comparing PAM-based values across treatment. All methods could LN LP R LFe none able R, or cultures. These results indicated most applications, necessary, furthermore do provide robust measurement UTEX 3037, potentially other, common freshwater cyanobacteria.