scholarly journals Diurnal Variation in Algal Acetylene Reduction (Nitrogen Fixation) in Situ

1975 ◽  
Vol 55 (2) ◽  
pp. 273-276 ◽  
Author(s):  
Larry N. Vanderhoef ◽  
Paul J. Leibson ◽  
Robert J. Musil ◽  
Chi-Ying Huang ◽  
Robert E. Fiehweg ◽  
...  
Keyword(s):  
Nitrogen Fixation ◽  
Diurnal Variation ◽  
Acetylene Reduction

Nitrogen Fixation and Phosphorus Turnover in a Hypertrophic Prairie Lake

1983 ◽  
Vol 40 (11) ◽  
pp. 1853-1860 ◽  
Author(s):  
B. G. Brownlee ◽  
T. P. Murphy
Keyword(s):  
Nitrogen Fixation ◽  
Light Intensity ◽  
Acetylene Reduction ◽  
Ammonia Volatilization ◽  
Molar Ratio ◽  
Short Term ◽  
Nitrogen Reduction ◽  
The Mean ◽  
Phosphorus Turnover

Nitrogen fixation by Aphanizomenon flos-aquae in a prairie lake in southwestern Manitoba was dependent on the light intensity and in situ oxygen concentrations. The mean molar ratio of acetylene reduction to nitrogen reduction was 5.8:1. High external ammonium concentrations did not appear to inhibit nitrogen fixation over the short term. Nitrogen fixation was not directly initiated by the bloom collapse. We propose that the coupled sequence of ammonia volatilization and nitrogen fixation was triggered by the bloom collapse and that the bloom collapse was caused by coprecipitation of orthophosphate with carbonates. 32PO4 turnover was most rapid during periods when the lake was opalescent, presumably due to carbonate precipitaton.

Seasonal and diurnal variation of nitrogenase activity (acetylene reduction) in barrel medic (Medicago truncatula Gaertn.) grown in pots

1978 ◽  
Vol 29 (5) ◽  
pp. 951 ◽  
Author(s):  
JJ Ruegg ◽  
AM Alston
Keyword(s):  
Nitrogen Fixation ◽  
Diurnal Variation ◽  
Medicago Truncatula ◽  
Acetylene Reduction ◽  
Time Course ◽  
Nitrogenase Activity ◽  
Seasonal Pattern ◽  
Molar Ratio ◽  
Multiple Use ◽  
Seasonal And Diurnal Variation

Seasonal and diurnal variation of nitrogenase activity in Medicago truncatula Gaertn. was measured by means of the acetylene reduction assay on plants grown in pots. In a glasshouse set at 20°C, the seasonal pattern of acetylene reduction (AR) activity was closely correlated with dry weight and photosynthetic area. Short-term fluctuations in AR activity were mainly associated with irradiance. Measurements made of the diurnal variation of AR activity showed that rates of AR at noon were 10–60% (average 33%) higher than the mean daily rates. Effects of defoliation and shading gave further evidence for the importance of light and recent photosynthate for nitrogen fixation in root nodules of legumes. Values for acetylene reduction integrated over time were highly correlated with the total amount of nitrogen in the plant. The molar ratio of acetylene reduced to nitrogen accumulated by the plants at the end of the experiment was 1.2 : 1. The significance of this value is discussed. Multiple use of the same plant material to study the time course of nitrogen fixation by the AR assay was found to be feasible under certain conditions.

In Situ Studies on Nitrogen Fixation with the Acetylene Reduction Technique

Science ◽  
1967 ◽  
Vol 158 (3800) ◽  
pp. 536-536 ◽  
Author(s):  
W. D. P. Stewart ◽  
G. P. Fitzgerald ◽  
R. H. Burris
Keyword(s):  
Nitrogen Fixation ◽  
Acetylene Reduction ◽  
Reduction Technique ◽  
In Situ Studies

Nitrogen fixation (acetylene reduction) in nonheterocystous cyanobacterial mats from the Dampier Archipelago, Western Australia

1989 ◽  
Vol 40 (2) ◽  
pp. 147 ◽  
Author(s):  
EI Paling ◽  
AJ McComb ◽  
JS Pate
Keyword(s):  
Nitrogen Fixation ◽  
Species Composition ◽  
Acetylene Reduction ◽  
Sea Water ◽  
The Other ◽  
Salinity Range ◽  
Cyanobacterial Mats ◽  
Microcoleus Chthonoplastes ◽  
Chlorophyll A Content

Discs punched from non-heterocystous cyanobacterial mats, one containing Microcoleus chthonoplastes, Oscillatoria sp. and Phormidium sp., the other Phorrnidium sp. and Aphanocapsa sp., were incubated for 23 days in artificial sea-water of salinity 0 to 140 g L-1. The chlorophyll a content of both mats increased over this salinity range, with lower increases above 100 g L-1. There was little change in the species composition of mats at salinities 240 g L-1; ≥ 40 g L-1, mats produced essentially monospecific thalli containing small quantities of the other species. Acetylene reduction ranged from zero at the highest salinity to a maximum of 1100-1500 pmol C2H2 reduced m-2 h-1 at 20-60 g L-1. Maximum fixation rates were two orders of magnitude higher than in situ measurements (8-60, mean 16 pmol C2H2 reduced m-2 h-1). The salinity range observed in the field was 40-60 g L-1, but maximum fixation rates in the field (60 Fmol C2H2 reduced m-2 h-1) were much lower than those observed in the laboratory.

A survey of nitrogen fixation (acetylene reduction) associated with Typha in Minnesota

1988 ◽  
Vol 66 (12) ◽  
pp. 2419-2423 ◽  
Author(s):  
Nancy A. Eckardt ◽  
David D. Biesboer
Keyword(s):  
Nitrogen Fixation ◽  
Regression Analysis ◽  
Acetylene Reduction ◽  
Substantial Reduction ◽  
Reduction Technique ◽  
Acetylene Reduction Activity ◽  
Typha Angustifolia ◽  
Reduction Activity ◽  
Nitrogen Requirement

The acetylene-reduction technique was used on soil–root cores to examine the three species of Typha (Typhaceae) found in Minnesota for differences in rates of nitrogen fixation by associated rhizosphere diazotrophs. In 20 cattail stands sampled in 1985, Typha angustifolia showed a tendency for lower acetylene-reduction activity per ramet, with an average of 2.9 μmol∙ramer−1∙d−1, than T. latifolia and T. ×glauca, with averages of 6.5 and 7.1 μmol∙ramet−1∙d−', respectively. Regression analysis showed no significant differences in these values due to the variability within as well as between stands, and fixation rates were uncorrelated with the pH, soil percent carbon, and soil moisture of the study stands. In 1986, in situ assays of soil–root cores of ramets of T. angustifolia and T. latifolia from adjacent monospecific stands produced average acetylene-reduction rates of 1.4 for T. angustifolia and 1.8 μmol∙ramet−1∙d−1 for T. latifolia, with a substantial reduction in variability within stands over the 1985 data. It is estimated that, contrary to previously published reports, populations of Typha may receive as little as 1–2% of their annual nitrogen requirement from nitrogen fixation.

Estimating Nitrogenase Activity of Faba Bean (Vicia faba) by Acetylene Reduction (Ar) Assay

1990 ◽  
Vol 17 (5) ◽  
pp. 489 ◽  
Author(s):  
Herdina ◽  
JH Silsbury
Keyword(s):  
Diurnal Variation ◽  
Vicia Faba ◽  
Faba Bean ◽  
Closed System ◽  
N2 Fixation ◽  
Acetylene Reduction ◽  
Nitrogenase Activity ◽  
Electron Flow ◽  
Specific Rate ◽  
Rooting Medium

Methods of conducting acetylene reduction (AR) assay were appraised for estimating the nitrogenase activity of nodules of faba bean (Vicia faba L.). Factors considered were: (i) disturbance of plants when removing the rooting medium; (ii) assay temperature; (iii) the use of whole plants rather than detached, nodulated roots; (iv) diurnal variation in nodule activity; and (v) a decline in C2H4 production after exposure to C2H2. Plants growing in jars of 'oil dry' (calcined clay) had the same AR activity when assayed in situ in a closed system as when assayed after removal of the rooting medium. Assay temperatures of 12.5, 17.5 and 22.5°C influenced the specific rate of AR with the optimum at 17.5°C. Removal of the shoot resulted in a rapid decrease in AR activity in both vegetative and reproductive plants but the effect was much larger in the latter. AR and respiration by nodulated roots were closely linked and both varied markedly over a diurnal 12 h/12 h cycle. Since no fluctuation was found after nodules were detached, diurnal variation in the respiration of nodulated roots is attributed to change in nodule activity. Half of the dark respiration of nodulated roots was associated with respiration of the nodules and thus largely with N2 fixation. Since the AR assay provides no information on how electron flow in vivo is partitioned between reduction of N2 and reduction of protons, diurnal variation in hydrogen evolution (HE) in air and Ar/O2 in an open system was used to estimate this partitioning. Diurnal variation in apparent N2 fixation estimated in this manner was examined at a 'low' PPFD (300 μmol m-2 s-1) and at 'high' (1300 μmol m-2 s-1) to explore whether variation could be attributed to change in carbohydrate supply. Although HE in air and in Ar/O2 were both closely linked with the respiration of the nodulated root, apparent N2 fixation showed only a slight diurnal variation at 'low' light and almost none at 'high'. Vegetative plants showed no C2H2-induced decline in activity with exposure to C2H2 but reproductive plants did. This difference appears to be an age effect rather than attributable to flowering per se, since a decline occurred even when plants were kept vegetative by disbudding. A closed system for AR assay appears satisfactory for vegetative faba bean but such an assay over a 40-min period during the reproductive stage would underestimate nitrogenase activity by about 20%.

Overexpression of the dctA gene in Rhizobium meliloti: effect on transport of C4 dicarboxylates and symbiotic nitrogen fixation

1992 ◽  
Vol 38 (6) ◽  
pp. 555-562 ◽  
Author(s):  
Vipin Rastogi ◽  
Monika Labes ◽  
Turlough Finan ◽  
Robert Watson
Keyword(s):  
Nitrogen Fixation ◽  
Acetylene Reduction ◽  
Symbiotic Nitrogen Fixation ◽  
Plasmid Stability ◽  
Rhizobium Meliloti ◽  
Mrna Synthesis ◽  
Dicarboxylate Transport ◽  
Fusion Strain ◽  
Tryptophan Operon ◽  
Specific Mrna

Symbiotic nitrogen fixation may be limited by the transport of C4 dicarboxylates into bacteroids in the nodule for use as a carbon and energy source. In an attempt to increase dicarboxylate transport, a plasmid was constructed in which the Rhizobium meliloti structural transport gene dctA was fused to a tryptophan operon promoter from Salmonella typhimurium, trpPO. This resulted in a functional dctA gene that was no longer under the control of the dctBD regulatory genes, but the recombinant plasmid was found to be unstable in R. meliloti. To stably integrate the trpPO-dctA fusion, it was recloned into pBR325 and recombined into the R. meliloti exo megaplasmid in the dctABD region. The resultant strain showed constitutive dctA-specific mRNA synthesis which was about 5-fold higher than that found in fully induced wild-type cells. Uptake assays showed that [14C]succinate transport by the trpPO-dctA fusion strain was constitutive, and the transport rate was the same as that of induced control cells. Acetylene reduction assays indicated a significantly higher rate of nitrogen fixation in plants inoculated with the trpPO-dctA fusion strain compared with the control. Despite this apparent increase, the plants had the same top dry weights as those inoculated with control cells. Key words: acetylene reduction, genetic engineering, nodule, plasmid stability, promoter.

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