Response of <i>Nodularia spumigena</i> to <i>p</i>CO<sub>2</sub> – Part 1: Growth, production and nitrogen cycling

Abstract

Abstract. Heterocystous cyanobacteria of the genus Nodularia form extensive blooms in the Baltic Sea and contribute substantially to the total annual primary production. Moreover, they dispense a large fraction of new nitrogen to the ecosystem when inorganic nitrogen concentration in summer is low. Thus, it is of ecological importance to know how Nodularia will react to future environmental changes, in particular to increasing carbon dioxide (CO2) concentrations and what consequences there might arise for cycling of organic matter in the Baltic Sea. Here, we determined carbon (C) and dinitrogen (N2) fixation rates, growth, elemental stoichiometry of particulate organic matter and nitrogen turnover in batch cultures of the heterocystous cyanobacterium Nodularia spumigena under low (median 315 μatm), mid (median 353 μatm), and high (median 548 μatm) CO2 concentrations. Our results demonstrate an overall stimulating effect of rising pCO2 on C and N2 fixation, as well as on cell growth. An increase in pCO2 during incubation days 0 to 9 resulted in an elevation in growth rate by 84 ± 38% (low vs. high pCO2) and 40 ± 25% (mid vs. high pCO2), as well as in N2 fixation by 93 ± 35% and 38 ± 1%, respectively. C uptake rates showed high standard deviations within treatments and in between sampling days. Nevertheless, C fixation in the high pCO2 treatment was elevated compared to the other two treatments by 97% (high vs. low) and 44% (high vs. mid) at day 0 and day 3, but this effect diminished afterwards. Additionally, elevation in carbon to nitrogen and nitrogen to phosphorus ratios of the particulate biomass formed (POC : POP and PON : POP) was observed at high pCO2. Our findings suggest that rising pCO2 stimulates the growth of heterocystous diazotrophic cyanobacteria, in a similar way as reported for the non-heterocystous diazotroph Trichodesmium. Implications for biogeochemical cycling and food web dynamics, as well as ecological and socio-economical aspects in the Baltic Sea are discussed.

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

“…(Sivonen et al, 1989;Finni, 2001;Vahtera et al, 2005). Calm conditions, a salinity of 7-8, temperatures >16 • C, and a N : P ratio <8 promote the formation of extensive Nodularia blooms in the sea surface layer (Wasmund, 1997). Degerholm et al (2006) suggested that Nodularia sp.…”

“…Since nitrogen fixation rates are supposed to increase under higher CO 2 concentrations (Wannicke et al, 2012) additional P (or changing C : N : P ratios) are required. This will be studied as part of two other investigations based on the same experimental setup.…”

“…This will be studied as part of two other investigations based on the same experimental setup. Wannicke et al (2012) and Endres et al (2013) focused on N-cycling, and exudation and extracellular enzyme activities, respectively. Here we investigated dissolved P pools, in particular their variation during the growth of the diazotrophic cyanobacterium Nodularia spumigena under conditions of pCO 2 elevation, and their contribution to Nodularia nutrition.…”

Effect of CO&lt;sub&gt;2&lt;/sub&gt; enrichment on bacterial metabolism in an Arctic fjord

“…However, this has been challenged by Liu et al (2010). For example, there is evidence that some functions such as nitrogen fixation (Wannicke et al, 2012), nitrification and bacterial activity are influenced by changing pCO 2 levels, which would influence biogeochemical processes (summarised in Liu et al, 2010 andin Weinbauer et al, 2011). Also, there is no study on the effect of pCO 2 on specific carbon metabolism components such as BR, BGE and BCD of natural bacterial communities in aquatic environments.…”

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

“…In the Baltic Sea, several studies of CO 2 effects have been undertaken on the organism level of fish (Frommel et al, 2013), zooplankton (Pansch et al, 2012;Vehmaa et al, 2012), macrophytes (Pajusalu et al, 2013), benthic species (Hiebenthal et al, 2013;Stemmer et al, 2013), and filamentous cyanobacteria (Czerny et al, 2009;Eichner et al, 2014;Wannicke et al, 2012). Studies on the impacts of elevated CO 2 at the ecosystem level, however, have thus far been limited to Kiel Bight in the western Baltic Sea (Engel et al, 2014;Rossoll et al, 2013;Schulz and Riebesell, 2013), which may fundamentally differ from other parts of the Baltic Sea.…”