Acetylene Reduction Rates Research Articles

Decomposition and potential nitrogen fixation inDicranopteris linearislitter on Mauna Loa, Hawai'i

ABSTRACTAs a consequence of its relatively high productivity in primary successional sites on Mauna Loa, Hawai'i, the mat-forming fernDicranopteris lineariscan influence attributes of soil detrital pools. Decomposition, nutrient release and rates of asymbiotic N fixation inDicranopterislitter were determined over an elevational range of oligotrophic sites. ‘Hot spots’ of nitrogen fixation occurred inDicranopterislitter, as evidenced by acetylene reduction rates as high as 22 nmol g−1h−1. However, potential N fixation rates for the entire litter mass were 0–0.1 g m−2y−1, less than other N inputs such as rainfall.Dicranopteris' decomposition rates were low compared to other tropical species, even under high temperature and rainfall conditions, with ≥50% of the original leaf and >77%of the stem mass remaining after 2 y of decomposition. Slow decomposition was related to high ligninrnitrogen ratios (56–129) in litter and above-ground positioning of unabscised, decomposing litter. As a result of its slow decomposition rates,Dicranopterisis an major contributor to soil detrital pools. Aggradation of the detrital pool is an important process whereby nutrients are accrued within these ecosystems. Consequently,Dicranopterisexerts an important influence on soil genesis and ecosystem development during primary succession on pahoehoe lava.

Nitrogen accumulation and nodule activity of field-grown ‘Jackson’ soybean in response to water deficits

Substantial evidence has accumulated that N 2 fixation in soybean ( Glycine max Merr.) is much more sensitive to drying soil than is leaf gas exchange and plant mass accumulation. In contrast, the soybean cultivar Jackson in controlled environments has been found to have N 2 fixation sensitivity to drying soil that is approximately equivalent to the sensitivity of leaf gas exchange. This study was undertaken to determine if Jackson behaved in a similar way under field conditions. N 2 fixation activity was measured by in situ acetylene reduction rates and N accumulation in shoots. Leaf gas exchange was measured as stomatal conductance and shoot mass accumulation. All measures in this field study indicated that N 2 fixation in Jackson decreased in response to soil drying in about the same proportion as leaf gas exchange. These results with Jackson were in contrast to those with the cultivar Biloxi in which N 2 fixation was decreased to a greater extent by drought than was leaf gas exchange.

Growth, heterocyst differentiation and nitrogenase activity in the cyanobacteria Anabaena variabilis and Anabaena cylindrica in response to molybdenum and vanadium

summaryThis paper reports effects of molybdenum and vanadium on Anabaena variabilis Kutz. (ATCC 29413) and Anabaena cylindrica Lemm. (PCC 7122), previously grown in NH4+‐containing medium deficient in Mo and V (–Mo–V) and then transferred to media lacking combined nitrogen. Diazotrophic growth of A. variabilis was dependent on the presence of Mo or V, with little growth occurring in their absence. Neither Mo nor V was required for heterocyst differentiation in either cyanobacterium, and the highest heterocyst frequencies occurred in cultures showing the lowest growth rates. Although A. cylindrica also showed Mo‐dependent diazotrophic growth and a low rate of growth in the absence of added Mo, the latter was inhibited by addition of 1 μM V. The rate of acetylene reduction by A. variabilis increased rapidly following addition of V to –Mo–V cultures, and increased ethane formation was detected in the acetylene reduction assays. Addition of Mo resulted in a smaller initial increase in the rate of acetylene reduction, but this was also accompanied by increased ethane formation, followed by a slow and much more extensive increase in acetylene reduction with a decrease in ethane formation. These observations indicate that nitrogenase polypeptides, probably those of a V‐nitrogenase, are synthesized in A. variabilis in the absence of added Mo or V, that added Mo can be incorporated into the V‐nitrogenase, and that synthesis of Mo‐nitrogenase is dependent on the presence of Mo. By contrast, A. cylindrica appears either to synthesize only a Mo‐nitrogenase, even in the absence of Mo (though 1 μM V inhibits its synthesis) or to synthesize a Mo‐ and V‐independent nitrogenase, but only in the absence of added Mo and V. Western blots using antisera against the Mo‐Fe and Fe proteins of the Mo‐nitrogenase of Rhodospirillum rubrum indicated the presence of Mo‐nitrogenase polypeptides in both Mo‐grown and –Mo–V grown A. cylindrica, providing evidence in support of the former possibility. Physiologically, the V‐nitrogenase of A. variabilis showed several distinct similarities to the Mo‐nitrogenase of A. cylindrica, including responses to metal concentrations as well as the above responses to addition of V and Mo, respectively.

Effect of plant photosynthesis, carbon sources and ammonium availability on nitrogen fixation rates in the rhizosphere of Zostera noltii

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 12:285-290 (1997) - doi:10.3354/ame012285 Effect of plant photosynthesis, carbon sources and ammonium availability on nitrogen fixation rates in the rhizosphere of Zostera noltii Welsh DT, Bourguès S, de Wit R, Auby I Rates of nitrogen fixation (measured as acetylene reduction) in the rhizosphere of the seagrass Zostera noltii were highly dependent upon plant photosynthetic activity being significantly stimulated at elevated CO2 concentrations and by light, both in the short-term and over diurnal cycles. Stimulation by light became insignificant when 5 mM sucrose was added to the sediment porewater, indicating that in the absence of added carbon sources, light stimulation was due to direct inputs of plant photosynthate to the rhizosphere. Addition of a range of carbon sources to the rhizosphere sediment stimulated rates of acetylene reduction, with this stimulation being significant for sucrose and lactate. Surprisingly, whilst low additions of ammonium to the sediment porewater (10 to 50 μM) inhibited 50% of acetylene reduction activity, approximately 30% of this activity persisted in the presence of 1 mM ammonium chloride; this indicating that in at least a proportion of the N-fixing community, nitrogenase activity was not regulated in the short term by the availability of alternative nitrogen sources. Acetylene reduction · Nitrogen fixation · Rhizosphere · Zostera noltii · Plant photosynthesis · Root exudates · Carbon sources · Ammonium Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 12, No. 3. Publication date: May 29, 1997 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 1997 Inter-Research.

N2 fixation and growth of legumes as affected by sulphur fertilization

The influence of three sulphur application rates in combination with two nitrogen application rates on N2 fixation and growth of different legumes was investigated. N was applied as N-labelled 15NH415NO3. The 15N isotope dilution technique was used to estimate N2 fixation. At both N increments dry matter yield was highest with high S supply. Independently of the N supply, the high S application rate resulted in a significantly higher N accumulation, which was mainly caused by a higher N2 fixation rate. With the grain legumes the weight of nodules was increased by the high S application rate. The higher number of nodules per pot with optimum S supply was the result of a better root growth. Rates of acetylene reduction correlated significantly with S supply.

Seasonal variation in rates of heterotrophic nitrogen fixation (acetylene reduction) in Zostera noltii meadows and uncolonised sediments of the Bassin d'Arcachon, south-west France

Nitrogen fixation (acetylene reduction) rates were measured over an annual cycle in meadows of the seagrass Z. noltii and uncolonised sediments of the Bassin d'Arcachon, south-west France, using both slurry and whole core techniques. Measured rates using the slurry technique in Z. noltii colonised sediments were consistently higher than those determined in isolated cores. This was probably due to the release of labile organic carbon sources during preparation of the slurries. Thus, in colonised sediments the whole core technique may provide a more accurate estimate of in situ activity. Acetylene reduction rates measured by the whole core technique in colonised sediments were 1.8 to 4-fold greater, dependent upon the season, in the light compared with those measured in the dark, indicating that organic carbon released by the plant roots during photosynthesis was an important factor regulating nitrogen fixation. In contrast acetylene reduction rates in uncolonised sediments were independent of light.

Seasonal variations in nitrogen-fixation (acetylene reduction) and sulphate-reduction rates in the rhizosphere of Zostera noltii: nitrogen fixation by sulphate-reducing bacteria

Nitrogen-fixation (acetylene reduction) rates were measured over an annual cycle in meadows of the seagrass Zostera noltii Hornem in the Bassin d'Arcachon, south-west France, between March 1994 and February 1995, using both slurry and whole-core techniques. Measured rates using the slurry technique consistently overestimated those determined on whole cores, probably due to the release of labile organic carbon sources as a result of root damage during preparation of the slurries. Thus, the whole-core technique may provide a more accurate estimate of in situ activity, since disturbance of physicochemical gradients of oxygen, sulphide, nutrients and the relationship between the plant roots and the rhizosphere microflora is minimised. Rates measured by the whole-core method were 1.8- to 4-fold greater (dependent upon season) in the light than those measured during dark incubations, indicating that organic carbon diffusing from the plant roots during photosynthesis was an important factor in regulating nitrogen fixation in the rhizosphere. Additions of sodium molybdate, a specific inhibitor of sulphate-reducing bacteria (SRB) inhibited acetylene-reduction activity by >80% as measured by both the slurry and whole-core techniques throughout the year, inferring that SRB were the dominant component of the nitrogen-fixing microflora. A mutualistic relationship between Z. noltii and nitrogen-fixing SRB in the rhizosphere, based on the exchange of organic carbon and fixed nitrogen is proposed. Acetylene- and sulphate-reduction rates showed distinct summer peaks which correlated with a reduced availability of ammonium in the sediment and the annual growth cycle of Z. noltii in the basin. Overall, these data indicate that acetylene reduction (nitrogen fixation) activity in the rhizosphere of Z. noltii was regulated both by the availability of organic carbon from the plant roots and maintenance of a low NH 4 + concentration in the vicinity of the plant roots due to efficient assimilation of NH 4 + by Z. noltii during the growth season. Nitrogenfixation rates determined from acetylene-reduction rates measured using the whole-core technique ranged from 0.1 to 7.3 mg N m-2d-1, depending on season, and were calculated to contribute between 0.4 and 1.1 g N m-2yr-1, or 6.3 to 12% of the annual fixed nitrogen requirement of Z. noltii.

Effects of formaldehyde-enriched mists on Pseudotsuga menziesii (Mirbel) Franco and Lobaria pulmonaria (L.) Hoffm

The atmosphere in some areas is polluted with formaldehyde (HCHO); however, little is known about effects of HCHO on plants at concentrations resembling those in polluted areas. The effects of simulated fogwater enriched with HCHO on seedlings of Pseudotsuga menziesii (Mirbel) Franco (Douglas fir) and pendants of Lobaria pulmonaria (L.) Hoffm. were assessed. Plants were treated with HCHO-enriched fog (target concentrations of 100, 500, and 1000 μ m) during five 4-night mist sessions. Growth and nitrogenase activity (acetylene reduction rate) for lichens and growth and timing of bud-break for Douglas fir were monitored. Nitrogenase activity was lowest in lichens treated at the highest HCHO concentration after all but the first mist session, and it declined significantly with increasing HCHO concentration after the final mist session ( R 2 = 0.60, p = 0.02 ). However, differences in nitrogenase activity among treatments were generally not statistically significant (most p values from ANOVAs were ≥ 0.20). Formaldehyde did not affect growth of the lichens. Budbreak of Douglas firs was slightly delayed and height growth was slightly depressed with increasing HCHO concentration, although effects were not statistically significant.

Peanut Nitrogen Fixation (C2H2 Reduction) Response to Soil Dehydration

Abstract Peanut (Arachis hypogaea L.) is commonly grown on sandy soils that are susceptible to water deficits. Because symbiotic nitrogen fixation in other grain legumes is especially sensitive to soil drying, the sensitivity of peanut nitrogen fixation to water deficits might be an important limitation on peanut production. This greenhouse study was undertaken to observe the response of nitrogen fixation (acetylene reduction) in six peanut cultivars to soil drying. In contrast to other grain legumes, peanut nitrogen fixation was relatively insensitive to soil drying. Acetylene reduction rates did not begin to decrease until soil water deficits had decreased to where leaf gas exchange was affected. These data indicated that restricted nitrogen fixation during drought stress is not likely to be a serious problem in peanut. Nevertheless, cultivar variation in drought sensitivity was identified indicating that genetic selection might further decrease the susceptibility of peanut nitrogen fixation to drought.

Influence of phosphorus on nitrogen fixation in chickpea cultivars

Abstract Phosphorus (P) is a major nutrient factor influencing nitrogen (N) accumulation and partitioning of photosynthates in plants, especially the symbiotic N2‐fixation in legumes. This study was conducted to investigate how P application (0, 20, 40, and 60 kg P2O5/ha) affects symbiotic N2‐fixation of three cultivars (C 235, Pusa 408, and Pusa 417) of chickpea (Cicer arietinum L.). Application of P in general significantly increased leaf area, shoot dry weight, and the rate of acetylene (C2H2) reduction. Phosphorus concentration of shoots and roots, soluble sugar content of nodules, and shoot N accumulation were also significantly increased, especially by P at the 40 kg P2O5/ha rate. The P concentration in nodules was, however, not affected by different levels of P. The Pusa 417 cultivar responded better than the others to the P treatments. Phosphorus‐deficient plants accumulated sugar in their leaves. The interaction effect was found significant on leaf area, shoot dry weight, nodule number, and shoot...

Factors Affecting the Acetylene to 15N2 Conversion Ratio in Root Nodules of Myrica gale L.

When nodules of actinorhizal plants are exposed to acetylene, there is often an initial peak rate of acetylene reduction followed by a decline and a partial recovery. Treatment of hydroponically grown Myrica gale L. with water deficiency or dark stress increased the magnitude of the acetylene-induced decline and decreased the extent of the recovery. When N2 fixation was measured with 15N2 in unstressed plants, the ratio of acetylene reduction (peak) to N2 fixation prior to acetylene exposure was 3.73 [plus or minus] 0.14 (mean [plus or minus] SE). This value does not differ significantly (P < 0.05) from the theoretical minimum value of 4.0. In water-stressed plants the conversion ratio for the peak rate was greater (4.32 [plus or minus] 0.10) and in dark-stressed plants it was lower (2.54 [plus or minus] 0.33) than 4.0. The conversion ratio for the recovered rate of acetylene reduction was much lower than 4.0 in all cases, with mean values ranging from 1.16 to 2.60. We conclude that the peak rate of acetylene reduction provides the most reliable estimate of N2 fixation. The recovered rate of acetylene reduction consistently underestimates N2 fixation, sometimes severely, and thus measurements of acetylene reduction made in closed systems also underestimate N2 fixation to varying degrees.

Potential Nitrogen Fixation During Primary Succession in Hawai`i Volcanoes National Park

I determined rates of acetylene reduction and estimated rates of nitrogen fixation in three sites that varied in soil age and nitrogen accumulation on Kilauea Volcano, Hawai'i. The major substrates in which acetylene reduction occurred were lichens of the genus Stereocaulon, liverworts, decaying leaf litter, and decaying wood. Estimated rates of nitrogen fixation were 0.3, 1.2, and 2.8 kg ha-' yr-' in an open-canopied 27 yr old site, a 200 yr old primary successional montane rain forest, and an -2000 yr old montane rain forest, respectively. The sum of nitrogen fixed by these sources plus nitrogen inputs in precipitation was insufficient to explain the quantity of nitrogen accumulated in the 200 yr old site.

Nitrogen fixation (acetylene reduction) on a coral reef

Nitrogen fixation rates associated with various substrates on a fringing reef at Eilat, Red Sea, were estimated by in situ acetylene reduction. High rates of acctylene reduction were associated with bare substrates, such as sand and dead coral skeletons. Low rates of acetylene reduction were associated with substrates covered by macroalgae or living coral tissue. Estimates of nitrogen fixation in various reef zones, based on these measurements, indicate that the sand-covered lagoon is responsible for more than 70% of the fixation in the reef. Consequently, the lagoon may serve as an important source of nitrogen for the coral reef community.

Nitrogen fixation and photosynthesis in high arctic forms of Nostoc commune

Nostoc commune, a colonial cyanobacterium, has been suggested as an important contributor of nitrogen to terrestrial ecosystems in the Canadian High Arctic, yet little is known about the ecophysiology of this organism in arctic environments. This study focused on the physiological performance of macroscopic colonies of N. commune found on Devon Island, N.W.T. The objectives were to examine the influence of temperature, colony morphology, and seasonal phenology on nitrogen fixation rates and the effects of light and temperature on photosynthesis. Maximum rates of acetylene reduction in N. commune (2119 nmol C2H4∙g−1∙h−1) were higher than those previously recorded for arctic N. commune but lower than values reported for temperate poulations. Depending on the time of the growing season, the temperature optimum for acetylene reduction varied from 15 °C to greater than 20 °C. Photosynthetic temperature optima did not occur below 20–25 °C (the highest temperatures measured). Light saturation of photosynthesis was reached at low levels of irradiance (100–150 μmol∙m−2∙s−1 PPFD). Acetylene reduction rates varied strongly with colony morphology. Thin, fragile, flattened colonies had higher rates than thicker, more resilient, flattened colonies or spherical colonies. Cold post-thaw temperatures appeared to delay the recovery of maximum nitrogen fixation rates for 2–3 weeks following the onset of the growing season. Compared with two other species of cyanobacteria present on Truelove Lowland (Gloeocapsa alpina and Gleotrichia sp.), N. commune had higher rates of nitrogen fixation. Key words: Nostoc commune, cyanobacteria, High Arctic, nitrogen fixation, photosynthesis.

Effects of Atmospheric NO2 on Azolla-Anabaena Symbiosis

Cultures of the water fern Azolla pinnata R, Br. exposed for 1 week to atmospheric NO2 (50, 100 or 200 nl l-1) induced additional levels of nitrate reductase (NaR) protein and nitrite reductase (NiR) activity. At low concentrations of NO2 (50 nl l-1), nitrate derived from NO2 provides an alternative N source for Azolla but does not affect rates of acetylene reduction. However, the symbiotic relationship between Azolla and its endosymbiont, Anabaena azollae is only affected adversely by high concentrations (100 and 200 nl l-1) of atmospheric NO2. The resultant decreases in rate of growth, nitrogen fixation, heterocyst formation, and overall nitrogen cycling are probably due to the additional accumulation of N products derived from higher levels of atmospheric NO2. Parallel increases in levels of polyamines suggest that Azolla partially alleviates these harmful effects by incorporating some of the extra NO2-induced N into polyamines.

Effects of Elevated Selenium Concentration on Selenium Accumulation and Nitrogen Fixation Symbiotic Activity of Melilotus indica L

Biological and soil factors which contribute to the successful colonization of an annual legume species, Melilotus indica L., in soils with elevated selenium (Se) were studied. This species was introduced into the Kesterson Reservoir in the fresh top soil that was brought in under the Kesterson Cleanup Action to fill lowering pond sites and prevent the formation of ephemeral pools containing hazardous levels of Se. In 4 years since its introduction, it has expanded its range of colonization from the fresh soil fill sites to the native soil sites and contributed 10 to 50% of biomass to the grassland communities. The plant and nodule tissue Se concentrations of the field grown plants were found to be negatively correlated with the soil sulfate concentration. Nutrient solution culture studies discovered that M. indica was able to accumulate 500 μg Se g −1 dry weight without a reduction of growth rate. Plants without nodulation were found to accumulate a greater amount of Se and more vulnerable to Se toxicity. Acetylene reduction rate measurements indicate that the nitrogen fixation symbiotic activity appears to be more susceptible to an elevated Se concentration than its host plant. M. indica is a winter weed, and it occurs naturally in the Se-rich soils. It grows actively over the winter and spring and complete its life cycle in May. If the root nodules and root tissues are incorporated into the soil, the rate of soil Se volatilization may be accelerated over the warm summer months. For disposal of the Se-rich plant materials the plant shoot tissues may be harvested for Se-deficient forage supplementation. Therefore, this species may be useful for field management and reclamation of Se-contaminated soils.

Humidity and light affect the growth, development and nitrogenase activity of stem nodules of Sesbania rostrata Brem.

The growth and nitrogenase activity of stem nodules of Sesbania rostrata Brem were strongly influenced by the humidity surrounding the nodule. Nodules developed under high humidity showed the fastest rates of growth and the highest specific nitrogenase activity (determined by acetylene reduction). Development of stem nodules in both the light and dark was similar and showed a similar lowering of growth and activity with decreasing humidity. Stem nodules developed in the dark were pale and unlike the dark green nodules that developed in the light, they did not have chloroplasts in the nodule cortex. Adventitious root development required darkness and relative humidities approaching 100%. In stem nodules that were grown at high humidity and subsequently exposed to lower humidities, there was only a small loss of nitrogenase activity, and high rates of acetylene reduction were maintained for 6 d after treatments were begun. The area of nodule attachment to the stem or root was measured in nodules of many sizes and found to be consistently greater in stem nodules. This may have implications for the comparative water balance of nodules on these two organs.

Effects of plant growth regulators on acetylene-reducing associations between Azospirillum brasilense and wheat

Treatment of wheat seedlings with the synthetic auxin, 2,4-dichlorophenoxyacetic acid (2,4-d), induced nodule-like structures or tumours (termed para-nodules) where lateral roots would normally emerge. The formation of these structures promoted increased rates of acetylene reduction at reduced oxygen pressure (0.02–0.04 atm) in seedling inoculated with Azospirillum brasilense, compared to seedlings inoculated without auxin treatment. Fluorescent microscopy, laser scanning confocal microscopy and direct bacterial counts all showed that the 2,4-d treatment stimulated internal colonization of the root system with azospirilla, particularly in the basal region of the nodular structures. Both colonization with azospirilla and acetylene-reducing activity were further stimulated by simultaneous treatment with another synthetic auxin, naphthaleneacetic acid (NAA) and, less reliably, with indoleacetic acid (IAA) and indolebutyric acid (IBA). These auxins produced shortening of many initiated lateral roots, although 20 times the concentration of NAA was required to achieve rounded structures similar to those obtained with 2,4-d. Treatment with NAA, IAA or IBA alone also stimulated colonization with azospirilla and acetylene reduction rates at 0.02 atm oxygen, but less effectively than by treatment with 2,4-d. Such exogenous treatments of wheat seedlings with synthetic growth regulators provide an effective laboratory model for studies on the development of a N2-fixing system in cereals.

Dinitrogen fixation (Acetylene reduction) and nitrogen accumulation in peas cultivated under the standard growth conditions

InPisum sativum cultivated under standard growth conditions the extent of N2 fixation with time estimated by the acetylene reduction assay (PN2F) and rates of the actual nitrogen accumulation of plant biomass (ANA) were calculated from six independent growth experiments. In the plants inoculated with indigenous soilRhizobium populations and cultivated on 0.63 mmol/L nitrate level the percentage PN2F:ANA ratios ranged from 25.7 to 61.5%. In peas inoculated with the inoculant strain the PN2F:ANA ratios were markedly higher, ranging from 59.8 to 65.1%. The plants cultivated on N-free nutrient solutions showed both PN2F:ANA and C2H4N2 ratios to be somewhat higher compared with the 0.63 mmol/L nitrate cultivated plants.

Identification of the Sources of Energy for Nitrogen Fixation and Physiological Characterization of Nitrogen-Fixing Members of a Marine Microbial Mat Community

Experimental manipulations of a microbial mat community were performed to determine sources of energy and reductant used for nitrogen fixation and to physiologically characterize the responsible diazotrophs. The dominant photolithotrophic members of this community were nonheterocystous cyanobacteria, but other potential nitrogen-fixing microorganisms were also present. Pronounced diel variability in rates of acetylene reduction was observed, with nighttime rates a factor of three to four higher than daytime rates. Acetylene reduction measured at night was dependent upon the occurrence of oxygenic photosynthesis the preceding day; mats incubated in the dark during the daytime reduced acetylene at rates comparable to those of light-incubated mats but were not able to reduce acetylene at the normally high rates the following night. The addition of various exogenous carbon compounds to these dark-incubated mats did not elicit nighttime acetylene reduction. Nighttime acetylene reduction apparently proceeds under anoxic conditions in these mats; the highest rates of acetylene reduction occur late at night. Additions of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (an inhibitor of oxygenic photosynthesis) to mats resulted in a pronounced stimulation of acetylene reduction during the day, but acetylene reduction the next night proceeded at greatly reduced rates (relative to untreated mats). This daytime stimulation, under the 3-(3,4-dichlorophenyl)-1,1-dimethylurea-induced anoxic conditions in the experimentally treated mats, was light dependent. These results suggest that nitrogen fixation in these mats may be attributed to the activities of nonheterocystous cyanobacteria utilizing storage products of oxygenic photosynthesis under anoxic conditions at night.