Lichenized unicellular cyanobacteria fix nitrogen in the light

2007 ◽  
Vol 85 (10) ◽  
pp. 1003-1006 ◽  
Author(s):  
P. D. Crittenden ◽  
X. Llimona ◽  
L. G. Sancho
Keyword(s):  
Diurnal Variation ◽  
Acetylene Reduction ◽  
Nitrogenase Activity ◽  
Reduction Rate ◽  
Carbon Flow ◽  
Diurnal Pattern ◽  
Fungal Symbiont ◽  
Minimum Rate ◽  
Isothermal Conditions ◽  
Acetylene Reduction Rate

Diurnal variation in N2-fixation (acetylene reduction) rate was measured in Thyrea girardii (Durieu & Mont.) Bagl. & Carestia and Thyrea confusa Henssen, lichens containing a unicellular cyanobacterial photobiont. In field assays, mean acetylene-reduction rates in the light were 25.8 ± 8.9 (n = 11) and 21.0 ± 5.6 nmol C2H4·g–1·h–1 (n = 13) for T. girardii and T. confusa, respectively, and the respective mean rates in the dark were 8.2 ± 1.8 (n = 26) and 13.5 ± 5.4 (n = 8) nmol C2H4·g–1·h–1. In laboratory assays under relatively isothermal conditions (ca. 19–22 °C), the maximum acetylene reduction rate (52.0 ± 6.0 nmol C2H4·g–1·h–1) was recorded in the light and the minimum rate (20.2 ± 6.0 nmol C2H4·g–1·h–1) in the dark. This diurnal pattern is contrary to expectations for unicellular cyanobacteria. We suggest carbon flow to the fungal symbiont reduces the potential for nitrogenase activity in the dark.

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%.

Nitrogen fixation associated with Scirpus atrovirens and other nonnodulated plants in Massachusetts

1978 ◽  
Vol 56 (21) ◽  
pp. 2636-2640 ◽  
Author(s):  
Todd M. Kana ◽  
John D. Tjepkema
Keyword(s):  
Nitrogen Fixation ◽  
Acetylene Reduction ◽  
Reduction Rate ◽  
Herbaceous Plant ◽  
Soil Incubation ◽  
Old Field ◽  
Fourfold Increase ◽  
Constant Rate ◽  
Moderate Rate ◽  
Acetylene Reduction Rate

Nitrogen fixation was measured using the acetylene reduction technique in soil cores of 13 nonnodulated, herbaceous plant species growing in mesic and wetland habitats. Six species that grew in a well-drained portion of an old field exhibited low rates of N2 fixation (7 g N∙ha−1∙day−1). A bulrush, Scirpus atrovirens, which grew in an area of compacted soil in the old field, showed a moderate rate of N2 fixation (30–100 g N∙ha−1∙day−1). These old field species exhibited a lag of only a few hours before a constant rate of acetylene reduction occurred. The estimated rates for the six wetland species were generally higher, and there was a lag such that the activity was still increasing after 20 h of incubation. N2 fixation in cores of S. atrovirens was primarily associated with the roots and adhering soil. Incubation of the cores in N2 for 24 h caused a fourfold increase in the acetylene reduction rate over that in air, although the rates during the first 4 h were similar.

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.

Nitrogen fixation and methane metabolism in a stream sediment–water system amended with leaf material

1981 ◽  
Vol 27 (5) ◽  
pp. 511-516 ◽  
Author(s):  
T.-Y. Tam ◽  
C. I. Mayfield ◽  
W. E. Inniss
Keyword(s):  
Methane Production ◽  
Acetylene Reduction ◽  
Reduction Rate ◽  
Water System ◽  
Stream Sediment ◽  
Leaf Material ◽  
Oxidation Of Methane ◽  
Acetylene Reduction Rate ◽  
Low Levels ◽  
Methane Metabolism

The reduction of acetylene and the production and oxidation of methane in a stream sediment–water system amended with either fresh leaves or autumn-shed leaves in the presence and absence of air were studied. Net methane production by the sediment–water system occurred only when leaf material was added, with fresh leaves giving 2.2 times the methane accumulation as autumn-shed leaves. Static incubation in the presence of air had little effect on net methane production, with such production being about the same as (with fresh leaves) or 79% of (with autumn-shed leaves) the anaerobic rates. Acetylene reduction was more affected by the presence of air, with anaerobic rates being at very low levels. The presence of fresh leaves was again stimulatory, with the acetylene reduction rate being 5.5-fold greater than that occurring with autumn-shed leaves.

Nodule biomass and acetylene reduction rates of red alder and Sitka alder on Vancouver Island, B.C.

1981 ◽  
Vol 11 (2) ◽  
pp. 282-287 ◽  
Author(s):  
Dan Binkley
Keyword(s):  
Nitrogen Fixation ◽  
Acetylene Reduction ◽  
Reduction Rate ◽  
Vancouver Island ◽  
Fixation Rate ◽  
Red Alder ◽  
Nodule Biomass ◽  
Closed Canopy ◽  
Management Alternative ◽  
Acetylene Reduction Rate

Three comparisons examined acetylene reduction rate and nodule biomass of red alder (Alnusrubra Bong.) and Sitka alder (Alnussinuata (Regel) Rydb.) on Vancouver Island, British Columbia. The first showed that the acetylene reduction rates of Sitka alder on four sites in early July 1979 varied from 8.8 to 22.0 μmol C2H2•g−1 dry nodule per hour; smaller nodules had the higher rates. In the second comparison, red alder and Sitka alder acetylene reduction rates for young plants were similar when assayed on the same day on the same site. Finally, acetylene reduction rates and nodule biomass were determined for both species growing in closed canopy stands on adjacent sites. In this pair of 20-year-old stands, red alder had double the acetylene reduction rate and three times the nodule biomass of the Sitka alder. Combining the nodule biomass estimates with the seasonal average reduction rates yielded current annual nitrogen fixation estimates (using C2H2) of 130 kg•ha−1•year−1 for the red alder plot and 20 kg•ha−1•year−1 for the Sitka alder plot. These estimates are within published ranges for the species. The lower fixation rate of Sitka alder is still substantial, relative to the nitrogen demands of conifers, and its shrub-like growth form makes it an attractive management alternative to red alder for biological nitrogen fixation in mixed conifer–alder plantations.

Identification of North American soybean lines that form nitrogen-fixing nodules with Rhizobium fredii USDA257

1992 ◽  
Vol 72 (1) ◽  
pp. 49-55 ◽  
Author(s):  
P. A. Balatti ◽  
S. G. Pueppke
Keyword(s):  
United States ◽  
North American ◽  
Acetylene Reduction ◽  
Reduction Rate ◽  
Nitrogen Fixing ◽  
Maturity Group ◽  
Midwestern United States ◽  
Rhizobium Fredii ◽  
Acetylene Reduction Rate

Rhizobium fredii produces nitrogen-fixing (Fix+) nodules on primitive soybean lines, but most strains do not form such structures with the small number of agronomically advanced lines that have been tested. We systematically evaluated the ability of R. fredii USDA257 to produce Fix+ nodules on 197 soybean lines available in the midwestern United States. Thirty-four of 197 such lines were Fix+. The frequency of this response was positively correlated with increasing maturity group. The acetylene-reduction rate of one advanced cultivar, Davis, was greater than that of the primitive cultivar, Peking. Our data indicate that the capacity to nodulate effectively with USDA257 is widespread in contemporary North American soybean lines.Key words: Acetylene-reduction, nodulation, Rhizobium, soybean

Dinitrogen fixation and nodulation by Frankia in Alnus incana as affected by inorganic nitrogen in pot experiments with peat

1983 ◽  
Vol 61 (11) ◽  
pp. 2956-2963 ◽  
Author(s):  
U. Granhall ◽  
T. Ericsson ◽  
M. Clarholm
Keyword(s):  
Acetylene Reduction ◽  
Nitrogenase Activity ◽  
Inorganic Nitrogen ◽  
Experimental Period ◽  
Alnus Incana ◽  
Nitrogen Application ◽  
Noticeable Effect ◽  
Essential Nutrients ◽  
Pot Experiments ◽  
Ph Level

The effects of single large or repeated, exponentially increasing applications of nutrients, with or without inorganic nitrogen and at two pH levels, on the growth, nodulation, acetylene reduction, and nutrient uptake in Alnus incana (L.) Moench were investigated in pot experiments with peat under controlled laboratory conditions. The repeated application of inorganic nitrogen did not suppress nitrogenase activity until the last 2 weeks, whereas an initial, large, nitrogen application effectively inhibited nodulation and activity throughout the 40-day experimental period. The mode of nitrogen application was thus found to be more important than the total amounts applied. Shoot length, leaf area, shoot–root relations, dry-matter production, and nitrogen contents of plants were determined at the end of the experiment, as well as the effect of Frankia inoculations. Nitrogenase activity was determined three times, at 0, 3, and 5 weeks. N2 fixation (balance/acetylene reduction) was found to be maximal, 55% of total nitrogen uptake, in minus-N pots with single applications of essential nutrients. The fastest growth was, however, noted in pots with single applications of all nutrients, including N. Among the latter, pots inoculated with Frankia showed the best growth, in spite of low nitrogenase activity. The only noticeable effect of a raised pH level was a reduced endophyte activity in minus-N pots with single applications of essential nutrients, due to increased N mineralization in the peat.

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