Response of <i>Nodularia spumigena</i> to <i>p</i>CO<sub>2</sub> – Part 3: Turnover of phosphorus compounds

Abstract

Abstract. Diazotrophic cyanobacteria form extensive summer blooms in the Baltic Sea driving the surrounding surface waters into phosphate limitation. One of the main bloom-forming species is the heterocystous cyanobacterium Nodularia spumigena. N. spumigena exhibits accelerated uptake of phosphate through the release of the extracellular enzyme alkaline phosphatase whose activity also serves as an indicator of the hydrolysis of dissolved organic phosphorus (DOP). The present study investigated the utilisation of DOP and its compounds (e.g., ATP) by N. spumigena during growth under different CO2 concentrations, in order to estimate potential consequences of ocean acidification on the cell's supply with phosphorus (P). Cell growth, the phosphorus pool, and four DOP compounds (ATP, DNA, RNA, and phospholipids) were determined in three setups with different CO2 concentrations (average 341 μatm, 399 μatm, and 508 μatm) during a 15-day batch experiment. The results showed stimulated growth of N. spumigena and a rapid depletion of dissolved inorganic phosphorus (DIP) in all pCO2 treatments. DOP uptake was enhanced by a factor of 1.32 at 399 μatm and of 2.25 at 508 μatm compared to the lowest CO2 concentration. Among the measured DOP compounds, none was found to accumulate preferentially during the incubation or in response to a specific pCO2 treatment. However, at the beginning 61.9 ± 4.3% of total DOP were not characterised but comprised the most utilised fraction. This is demonstrated by the decrement of this fraction to 27.4 ± 9.9% of total DOP during the growth phase with a preference at high pCO2. Our results indicate a stimulated growth of diazotrophic cyanobacteria at increasing CO2 concentrations which is accompanied by increasing utilisation of DOP as an alternative P source.

Effects of CO<sub>2</sub> perturbation on phosphorus pool sizes and uptake in a mesocosm experiment during a low productive summer season in the northern Baltic Sea

“…Thus, variations and differences in the treatments can be overseen at daily sampling. Unger et al (2013) demonstrated that an accelerated PO 4 uptake by the cyanobacterium Nodularia spumigena under elevated CO 2 incubations could only be observed during the first hours. Thereafter, the differences were balanced and the same level of radiotracer labelling was reached in all treatments.…”

“…The final volume was recorded. The dATP concentrations were measured in triplicate using the firefly bioluminescence assay and a Sirius luminometer (Berthold Detection Systems Pforzheim, Germany), as described by Unger et al (2013). Standard concentrations were prepared as described above, using aged Baltic Sea water and six ATP concentrations (adenosine 50-triphosphate disodium salt hydrate, SigmaAldrich, A2383) ranging from 1 to 20 nmol L −1 .…”

“…Dissolved DNA and RNA Dissolved DNA and RNA (dDNA and dRNA) concentrations were determined according to Karl and Bailiff (1989) and as described by Unger et al (2013). For each sample, 200 mL of the filtrate was gently mixed with the same volume of ethylene-diamine-tetracetic acid (EDTA, 0.1 M, pH 9.3, Merck, 1.08454) and 4 mL of cetyltrimethyl-ammonium bromide (CTAB, Sigma-Aldrich, H5882) and stored frozen at −20 • C for at least 24 h. After thawing the samples, the precipitate was collected onto combusted (450 • C, 6 h) glass fiber filters (25 mm, GF/F Whatman), placed into annealed vials, and stored frozen at −80 • C until further analysis.…”

“…In CO 2 manipulation experiments, particulate phosphorus dynamics were studied to determine effects on C : P stoichiometry of phytoplankton (Riebesell and Tortell, 2011;Sugie and Yoshimura, 2013) and PO 4 concentration dynamics to estimate its utilization . CO 2 effects on phosphorus pool sizes and PO 4 uptake have so far been studied by Tanaka et al (2008) in the Raunefjorden, Norway and by Unger et al (2013) and Endres et al (2013) in laboratory experiments with cultures of Nodularia spumigena. In order to reduce the gap of knowledge, we studied the impact of elevated CO 2 on phosphorus pool sizes, the DOP composition, and PO 4 uptake of a northern Baltic Sea plankton community.…”

Colorimetric Chemical Differentiation and Detection of Phosphorus in Eutrophic and High Particulate Waters: Advantages of a New Monitoring Approach

“…The functional differentiation of organic and inorganic P requires a big effort which takes much time. It is hardly realizable to measure organic P in its entirety rather its single compounds like DNA and RNA or ATP which have a minor part in the DOP (Unger et al, 2013). Furthermore, when using the molybdenum blue method, labile P components other than DIP, e.g., labile organic P or colloidal bound P, may also be bound to the molybdenum blue complex (Rigler, 1968;Stainton, 1980;Haygarth and Sharpley, 2000;Jarvie et al, 2002).…”