Abstract
Nitrogen is an essential nutrient for all life forms and its availability is periodically limited in marine and freshwater ecosystems. To optimize the growth of the freshwater microalga Chlamydopodium fusiforme and to investigate the cell acclimation process to different amounts of nitrogen, we grew cells in Bristol and BG11, under fixed conditions of 10 h:14 h light/dark cycle. Cultures grown in BG11 exhibited higher biomass accumulation, reaching a cell dry weight of 1.94 ± 0.1 g L−1, while in Bristol it reached 1.58 ± 0.1 g L−1. In cells grown in BG11, chlorophyll content increased continuously up to 79.6 mg L−1 (9th day), while in Bristol it was much lower (29.5 mg L−1). This fact caused a strong difference in their spectrally averaged optical cross-section normalized to chlorophyll a (a*), and consequently in their photosynthetic performance (oxygen evolution and electron transport rates). Carotenoid content followed a similar pattern. It was interesting to note that despite this great difference in chlorophyll concentration, both photosynthesis rate and cell dry weight were not affected proportionally. The chlorophyll a fluorescence measurements indicated a stable effective quantum yield of photosystem II in both culture conditions. During the dark phase of the cycle we observed in both cultures a remarkable reduction of both electron transfer and photosynthesis rates, while maximum quantum yield of PSII remained stable (0.74 ± 0.01). This indicated that the reduction in both photosynthesis rate and maximum electron transport rate (ETRmax) observed during the dark phase were not due to damage of PSII reaction centers but rather to reduced flow of electron subsequent to PSII. Recovery of the fully photosynthetic capacity required about 1 h of illumination.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.