High nutrient requirement on the photosynthetic performance of a diatom species of the genus Nitzschia (Bacillariophyta) isolated from the high-altitude wetland, Salar de Huasco, Chile

This study characterizes the ecophysiological responses and growth dynamics of Nitzschia palea isolated from Salar de Huasco, Chile, a high-altitude wetland located at 3800 m above sea level. The culture was maintained at 17 degrees C under cool-white fluorescent light with a 14:10 h light/dark photocycle and a photon flux of 50 mu mol photons m-2 s-1. The diatom was identified morphologically and genetically, with phylogenetic analysis confirming its close relationship to known N. palea strains. Photophysiological responses were measured along with a series of media and temperature conditions in N. palea strain. Modified f/2 media supplemented with different concentrations of Si, Se and vitamins were tested. Subsequently, growth in the double-Si f/2 media was assessed at three different temperatures. Lastly, the diatom strain was incubated at 17 degrees C and 27-29 degrees C in f/2 + double-Si (NN: non-extra nutrient addition) and a highly eutrophic state of f/2 (WN: with nutrient enrichment addition). The highest growth was observed using the f/2 media WN at 17 degrees C (day 5, 4.46 x 105 +/- 3.15 x 104 SD cells mL-1). Temperature significantly influenced growth; 17 degrees C supported higher cell densities and more stable photosynthetic parameters compared 27-29 degrees C. Nutrient enrichment further enhanced photosynthetic efficiency (alpha ETR) and maximal quantum yield (Fv/Fm), particularly under control temperature conditions. Photosynthetic performance, assessed via rapid light-response curves, showed significant temperature and nutrient dependent variation. Nitzschia palea cultures at 27-29 degrees C exhibited increased in relative maximal ETR (rETRmax,184.1 mu mol m-2 s-1) compared to control conditions. In nutrient enriched treatments, photosynthetic efficiency peaked on day 5, but declined by day 8. These findings highlight the adaptive capacity of N. palea to fluctuating environmental conditions and underscore its potential as a model organism for studying diatom responses to nutrient and temperature stress in extreme ecosystems.