Abstract
In freshwaters, algal species are exposed to different inorganic nitrogen (Ni) sources whose incorporation varies in biochemical energy demand. We hypothesized that due to the lesser energy requirement of ammonium (NH4+)‐use, in contrast to nitrate (NO3-)‐use, more energy remains for other metabolic processes, especially under CO2‐ and phosphorus (Pi) limiting conditions. Therefore, we tested differences in cell characteristics of the green alga Chlamydomonas acidophila grown on NH4+ or NO3- under covariation of CO2 and Pi‐supply in order to determine limitations, in a full‐factorial design. As expected, results revealed higher carbon fixation rates for NH4+‐grown cells compared to growth with NO3- under low CO2 conditions. NO3-‐grown cells accumulated more of the nine analyzed amino acids, especially under Pi‐limited conditions, compared to cells provided with NH4+. This is probably due to a slower protein synthesis in cells provided with NO3-. In contrast to our expectations, compared to NH4+‐grown cells NO3-‐grown cells had higher photosynthetic efficiency under Pi‐limitation. In conclusion, growth on the Ni‐source NH4+ did not result in a clearly enhanced Ci‐assimilation, as it was highly dependent on Pi and CO2 conditions (replete or limited). Results are potentially connected to the fact that C. acidophila is able to use only CO2 as its inorganic carbon (Ci) source.
Highlights
Green algae (Chlorophyta), with around 6,500 recognized species (Guiry & Guiry, 2017), can be found in highly diverse habitats, such as in soils, streams, lakes, and even on stones, trees, and animals (Andersen, 1992)
Contrary to our hypothesis that an acidophilic alga might have a preference for ammonium as an Ni‐source, and possibly lacks nitrate reductase (NR) ac‐ tivity as an adaptation to their environment, which consists of 91% NH+4 (Bissinger et al, 2000), we found NR activity in C. acidophila
This effect was only observed under a low CO2 condition, which is consistent with our hypothesis that effects from the Ni‐source might be enhanced under low CO2 due to energy consuming concentrating mechanisms (CCMs) (Raven & Beardall, 2014) or a de‐ creased cellular ATP content (Raven et al, 2014)
Summary
Green algae (Chlorophyta), with around 6,500 recognized species (Guiry & Guiry, 2017), can be found in highly diverse habitats, such as in soils, streams, lakes, and even on stones, trees, and animals (Andersen, 1992). It was previously shown that the influence of the Ni‐source on dif‐ ferent physiological parameters might depend on other factors, such as light (Ruan & Giordano, 2017) and CO2 (Giordano, 1997), but to our knowledge there are no studies combining two factors involved in energy and carbon metabolism in comparison with the effect of a different Ni‐source As both Ci (Tittel, Bissinger, Gaedke, & Kamjunke, 2005) and Pi (Spijkerman 2008) have been identified as potential (co‐)limiting factors for C. acidophila in the acidic Lake 111 (Spijkerman, Stojkovic, Holland, Lachmann, & Beardall, 2016), we included both factors in our setup. The influence of provided Ni‐sources on the ecophysiology of C. acidophila was examined by measuring a wide range of physiological parameters such as Ci‐uptake kinetics, amino acid levels, and NR activity
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
