The Bunsen gas solubility coefficient of ethylene as a function of temperature and salinity and its importance for nitrogen fixation assays

Nitrogenase activity, indicative of N 2 fixation, was measured in the surface waters along a north-south transect in the eastern Atlantic Ocean, from Texel (The Netherlands, 53uN) to Cape Town (South Africa, 35uS) using a sensitive on-line, near real-time acetylene reduction assay. From the beginning of January to the end of February 2000 nitrogenase activity was detected in varying rates, but only between 14uN and 13uS latitudes. Dark incubations yielded an average activity of 2.2 (6 2.4) mmol m 22 d 21 N, but light increased the activity to 3.7 (6 2.9) mmol m 22 d 21 N. However, nitrogenase activity in the light was sensitive to O 2 doubling to 7.6 (6 12.7) mmol m 22 d 21 N when the incubation was anaerobic. In the area where N 2 fixation occurred, phosphate concentrations were fourfold lower than in the area where N 2 fixation was absent, while silicate levels were higher. The water temperature in the area with N 2 fixation was 28uC, while in the adjacent area the temperature was 3uC lower, which might have prevented the proliferation of diazotrophic cyanobacteria. Action spectra revealed that chlorophyll a, phycocyanin, and phycoerythrin are the light-harvesting pigments supporting nitrogenase activity. In one area in the northern latitudes, potential nitrogenase activity was highest during daytime, which is characteristic for Trichodesmium. In areas with a high potential nitrogenase activity, surface waters were dominated by a phycoerythrin-containing cyanobacterium. Since nitrogenase activities were highest at night, these cells may have been unicellular cyanobacteria like Crocosphaera.

Section: Methodsmentioning

confidence: 99%

Nitrogen fixation along a north‐south transect in the eastern Atlantic Ocean

Staal

Hekkert

Brummer

et al. 2007

“…Subsamples of the headspace were removed immediately after the injection of acetylene and at the end of the incubation, and ethylene was analyzed by a flame ionization gas chromatograph (GC-17A, Shimadzu). Then, the ethylene production during the incubation was calculated after Breitbarth et al (2004). The produced ethylene was converted to fixed nitrogen with a molar ratio of 4 : 1.…”

Section: Methodsmentioning

confidence: 99%

Latitudinal distribution of diazotrophs and their nitrogen fixation in the tropical and subtropical western North Pacific

Kitajima

Furuya

Hashihama

et al. 2009

115

Latitudinal distribution of diazotrophs and their nitrogen (N 2 ) fixation activity were investigated in the western North Pacific in winter (Nov to Dec 2004) and summer (May to Jun 2005) along meridional transects from 37uN to the equator. N 2 fixation activity in whole seawater and seawater passed through a 10-mm filter was assayed by acetylene reduction. The whole-water N 2 fixation was markedly elevated in winter throughout the study area compared to that in summer, probably due to the increased upward supply of phosphate as a result of deeper mixed layer in winter. During both periods a distinct latitudinal variation was observed in N 2 fixation of the whole-water samples at the surface; further, higher activity was observed between the Kuroshio Extension and the salinity front in the North Equatorial Current than in the neighboring areas. The elevated N 2 fixation was primarily ascribed to ,10-mm diazotrophs during both seasons. Flow cytometry conducted in summer revealed that distribution of nanoplanktonic cyanobacteria was closely correlated with that of N 2 fixation activity in the ,10-mm fraction, indicating that nanoplanktonic cyanobacteria were the major diazotrophs in that area. In contrast, microplanktonic diazotrophs, Trichodesmium spp. and Richelia intracellularis exhibited different latitudinal distributions from that of nanoplanktonic cyanobacteria, with maximum numerical abundance of R. intracellularis around 8uN and 30uN, and that of Trichodesmium spp. at 26.5uN. Few microplanktonic diazotrophs occurred in the winter. The distribution of the diazotrophs and their N 2 fixation activity may be controlled by the supply of phosphate and aeolian dust deposition.

“…Samples were gently agitated to equilibrate gas concentrations between the headspace and culture samples after injecting acetylene and before measuring ethylene concentrations. We used a Bunsen coefficient for ethylene of 0.082 (Breitbarth et al 2004) and an ethylene production : N 2 fixation rate ratio of 3 : 1, and we calculated N 2 -fixation rates over 14 h (this included the 12 h dark cycle and the first 2 h of the light cycle).…”

Section: Methodsmentioning

confidence: 99%

Colimitation of the unicellular photosynthetic diazotroph Crocosphaera watsonii by phosphorus, light, and carbon dioxide

Garcia

Hutchins

2013

We describe interactive effects of total phosphorus (total P 5 0.1-4.0 mmol L 21 ; added as H 2 NaPO 4 ), irradiance (40 and 150 mmol quanta m 22 s 21 ), and the partial pressure of carbon dioxide (P CO2 ; 19 and 81 Pa, i.e., 190 and 800 ppm) on growth and CO 2 -and dinitrogen (N 2 )-fixation rates of the unicellular N 2 -fixing cyanobacterium Crocosphaera watsonii (WH0003) isolated from the Pacific Ocean near Hawaii. In semicontinuous cultures of C. watsonii, elevated P CO2 positively affected growth and CO 2 -and N 2 -fixation rates under high light. Under low light, elevated P CO2 positively affected growth rates at all concentrations of P, but CO 2 -and N 2 -fixation rates were affected by elevated P CO2 only when P was low. In both high-light and low-light cultures, the total P requirements for growth and CO 2 -and N 2 -fixation declined as P CO2 increased. The minimum concentration (C min ) of total P and half-saturation constant (K K ) for growth and CO 2 -and N 2 -fixation rates with respect to total P were reduced by 0.05 mmol L 21 as a function of elevated P CO2 . We speculate that low P requirements under high P CO2 resulted from a lower energy demand associated with carbon-concentrating mechanisms in comparison with low-P CO2 cultures. There was also a 0.10 mmol L 21 increase in C min and K K for growth and N 2 fixation with respect to total P as a function of increasing light regardless of P CO2 concentration. We speculate that cellular P concentrations are responsible for this shift through biodilution of cellular P and possibly cellular P uptake systems as a function of increasing light. Changing concentrations of P, CO 2 , and light have both positive and negative interactive effects on growth and CO 2 -, and N 2 -fixation rates of unicellular oxygenic diazotrophs like C. watsonii.Within the past 5 yr, new attention has focused on the effects of elevated partial pressures of carbon dioxide (P CO 2 ) on marine dinitrogen (N 2 ) fixation. In particular, three studies initiated this interest by documenting increased N 2 -fixation rates by Trichodesmium erythraeum in response to elevated P CO 2 (Barcelos e Ramos et al. 2007;Hutchins et al. 2007;Levitan et al. 2007). It is, however, particularly important to answer questions about how multiple environmental factors might change and interact with rising P CO 2 to affect ocean biogeochemical cycles. Hutchins et al. (2007) examined the combined effects of P CO 2 , temperature, and P concentration on N 2 -fixation rates by two strains of T. erythraeum. That study concluded that P CO 2 limitation of N 2 -fixation rates by T. erythraeum was independent of P concentration because the relative magnitude of elevated P CO 2 effects on growth and N 2 -fixation rates was nearly identical in P-limited and Preplete cultures. This finding suggests that decreases in P concentrations, which are likely to accompany future changes in surface ocean warming and stratification (Hutchins et al. 2009), would not influence the effect of elevated P CO 2 on oceanic N 2 ...