Rates Of Acetylene Reduction Activity Research Articles

Spartina alternifloraDieback Recovery Correlates with Increased Acetylene Reduction Activity in Saltmarsh Sediments

Spartina alterniflorasalt marshes occasionally exhibit areas where the plants have all died off for no apparent reason. These dieback areas remain devoid of plant growth for months to years. An analysis of microbial acetylene reduction activity (ARA) and porewater chemistry of four such diebacks has been carried out on marshes in the Cooper River estuary, South Carolina, U.S.A. Four different diebacks were studied and sediments in all of them showed low rates of ARA, relative to sediments from the control areas which were populated by healthyS. alternifloraplants. The pore water of all the dieback sediments had higher salinities than the controls when this study began, but this trend was not consistent over the 18-month study period. Furthermore, dissolved ammonium and sulfide in the pore water, microbial biomass, organic matter and macro-organic matter content did not show a consistent trend differentiating the control and dieback sediments over this study period. During the course of this study, one of the diebacks recovered and the recolonisation of the barren area with healthy plants correlated with a full recovery of sediment ARA. The return of ARA to the sediments of this recovered marsh could not be correlated, however, with any of the porewater parameters measured (including NH4+), nor with any of the sediment characteristics. It is concluded that the lower levels of bacterial ARA in the diebacks may be due to the lack of essential factors associated with healthy spartina plants.

Nitrogenase activity, nodulation and seed production inVicia fabaas affected by methabenzthiazuron

SUMMARYThe effects of recommended application rates of the herbicide methabenzthiazuron (MBT) (2·5 and 4 kg ha-1) on vegetative growth, nodulation and N2fixation in faba bean plants were studied in the field at Barcelona during 1990 and 1991. Nodulation, specific nitrogenase activity (SNA) of excised nodules, dry weight of plants and seed nitrogen content at harvest were compared in MBT-treated, hand-weeded (HW) and control plants. In 1990 the higher MBT application (4 kg ha-1) caused a decrease in nodulation and acetylene reduction activity (ARA) per plant during the mid-period of pod-fill, and also in vegetative growth, seed production and N content of seeds, whereas the lower rate (2·5 kg ha-1) did not have a significant effect on any of these factors. However, in 1991, growth and herbicide effects were different from those in the previous year. No inhibitory effect of MBT on nodulation, SNA or ARA per plant was observed and vegetative growth, seed production and N content of seeds were not significantly different from those of plants from HW plots. In 1991, both 4 kg ha-1of MBT and the HW treatment caused a stimulatory effect on seed N recovery and yield compared to control plants. Rates of ARA per plant at late pod-fill were positively related to N recovery by seeds. These differences could have been due to the low rainfall in 1990, which may have permitted MBT to remain in the soil for a longer period and to inhibit N fixation and plant growth in theVicia fabacrop.

Biological nitrogen fixation (acetylene reduction) associated with decomposing Avicennia marina leaves in the Beachwood Mangrove Nature Reserve

Nitrogen fixation of decomposing Avicennia marina (Forssk.) Vierh. leaves was studied over a period of 16 weeks under exposed and submerged conditions. Rates of acetylene reduction activity (ARA) were highest under exposed conditions and reached a maximum after three to four weeks. Percentage total nitrogen increased during decomposition, the increase being greatest under submerged conditions, but this was not directly related to nitrogen fixation. Bacteria were considered to be the main agents of nitrogen fixation. Rates of decomposition were highest under exposed conditions. The contribution of nitrogen fixation to the nitrogen budget is significant.

Nitrogenase activity in the papyrus swamps of Lake Naivasha, Kenya

Nitrogenase activity (acetylene reduction activity) was found to occur universally in the Cyperus papyrus swamp in Lake Naivasha. Low rates of acetylene reduction activity (0.9–104.9 nmol C2H4 g d.wt. roots-1 h-1) were associated with excised roots of C. papyrus but higher rates of activity (89.0–280.4 nmol C2H4 g d.wt. roots-1 h-1) were associated with intact root systems of the plant. It was estimated that nitrogen fixation associated with young roots alone could supply about 26% of the nitrogen requirements of growing papyrus plants. Acetylene reduction activity in the lake bottom sediments was generally low and associated with adjacent papyrus stands. Plate counts of putative aerobic and facultatively anaerobic N2-fixing bacteria associated with papyrus roots showed the presence of high numbers of diazotrophs (5.4 × 106 CFU g d.wt. roots-1). Fewer numbers of N2-fixing bacteria were detected in the sediments (1.9 × 103-3.2 × 104 CFU g d.wt. sediment-1).

Water stress induced changes in concentrations of proline and total soluble sugars in nodulated alfalfa (Medicago sativa) plants

Susceptibility of alfalfa (Medicago sativa L. cv. Aragón) nodules and leaves to water stress has been investigated. Nodule acetylene reduction activity (ARA), leaf CO2 exchange rate (CER) as well as soluble protein, proline and total soluble sugar (TSS) contents were determined during drought. Water status was estimated as water potential (Ψw) and Relative water content (RWC) of the respective tissues. Maximum rates of ARA required higher Ψw than CER. Nodules had lower RWC for a given Ψw than leaves. Water stress reduced soluble protein content in both tissues; however, the decline in soluble protein content was detected at greater Ψw in nodules than in leaves. Proline and TSS increased in leaves and nodules, and again the threshold Ψw triggering such accumulation was higher in nodule tissues. Oior results suggest that alfalfa nodules are more susceptible to water shortage than leaves. Effects of accumulated TSS and proline upon leaf and nodule physiology are discussed in relation to protein stability (proline), pH control (proline) and osmotic adjustment (proiine and TSS). The TSS accumulation induced by water stress suggests that substrate shortage would not be the primary effect of drought on nodule activity.

The Relations of Haemoglobin and Lignin-like Compounds to Acetylene Reduction in Symbiotic Casuarina

Nodules from six Casuarina symbioses ( Casuarina cunninghamiana, C. equisetifolia, and C. glauca inoculated with each of two different Frankia sources) were evaluated for (i) concentrations of haemoglobin (measured as CO-reactive haem) at 124, 144 and 165 d after inoculation, (ii) acetylene reduction and (iii) occurrence of lignin-like compounds in cell walls of the nodules at 165 d after inoculation. Haemoglobin concentration and the occurrence of lignin-like compounds were related to acetylene reduction at final harvest. Concentration of haemoglobin in nodules ranged from 1.56 to 22.27 nmol haem (g FW) -1 . There were marked plant species- Frankia interactions. At final harvest plant growth was greatest in C. cunninghamiana inoculated with Frankia inoculum designated SI, while haemoglobin concentration was intermediate in this symbiosis. Acetylene reduction activity was detected in all the symbioses except C. equisteifolia inoculated with SI, and was highest in C. glauca inoculated with SI. Haemoglobin concentration per fresh weight nodule and acetylene reduction per plant were positively correlated (r= 0.84, n= 12). The highest levels of cumulative nitrogen fixation were always associated with the highest haemoglobin concentrations and the highest rates of acetylene reduction activity. Nitrogen content was lowest in C. equisetifolia inoculated with SI (23.89±3.07 mg) and highest in C. cunninghamiana inoculated with the same inoculum (217.2±22.5 mg). Irrespective of symbiotic performance, lignin-like compounds were found in the cell walls of the nodules in all symbioses in this study. The cells containing these compounds were mainly localized in the infected areas of the nodule. The roles of haemoglobin and occurrence of lignin-like compounds in relation to nitrogen fixation in Casuarina symbioses are discussed.

Some observations on the oxygen sensitivity and seasonal variations of the nitrogenase activity associated with excised soil-plant cores of Phragmites australis (Cav.) Trin.

The sensitivities of Phragmites soil-plant core and litter nitrogenase activity were assayed by the acetylene reduction assay method. Acetylene reduction activity (ARA) of soil-plant cores incubated under ambient O 2 concentration, increased with increasing pC 2H 2 up to 0.20 atm. A Km of 1.05 atm and V ax of 234 nmol C 2H 2g −1h −1 were calculated. The highest rates of ARA overall occurred in the 8–16 cm zone. Within the core profile, mean rates varied with depths: 0–8, 8–16 and 16–20 cm, and incubation pO 2. In the 0–8 cm zone, ARA at pO 2 0.0, 0.10 and 0.20 atm did not differ significantly, but in the 8–16 and 16–20 cm zones, the highest rates were obtained at pO 2 0.0 atm. A lag of approximately 5 h preceded linear rates of litter ARA in time course assays. Change from aerobic to anaerobic atmospheres and the reverse substantially reduced core and excised root ARA for a period. Core ARA increased with incubation temperature between 0 and 20°C; mean rates were the same at 20 and 25°C. ARA, numbers of diazotrophs, soil temperature, pH and Eh showed a seasonal pattern of variability. The highest rates of ARA were obtained between mid May and June; peak numbers of diazotrophs were counted between June and mid July. Variations in soil pH were slight, but the most obvious change (6.3–7.5) occurred when the soil was warmest and most reduced.

Biological nitrogen fixation (acetylene reduction) associated with blue-green algal (cyanobacterial) communities in the Beachwood Mangrove Nature Reserve. I. The effect of environmental factors on acetylene reduction activity

Nitrogen fixation of blue-green algae (cyanobacteria) associated with Avicennia marina (Forssk.) Vierh. pneumatophores and wet and dry surface sediments was investigated in the Beachwood Mangrove Nature Reserve by means of the acetylene reduction technique. Studies revealed percentage moisture and temperature to be the prime factors influencing ARA (acetylene reduction activity) in these habitats and rates were highest under submerged conditions and at 22°C. High concentrations of inorganic nitrogen (between 1 and 5 mg l−1) significantly depressed ARA in all habitats. Increases in ARA occurred with increase in light intensity up to 40 μE m−2 s−1, with negligible dark rates being recorded in association with the wet and dry surface sediments. Significant dark rates of ARA and stimulation of ARA by sucrose in association with the pneumatophores indicated that bacteria may also be contributing to ARA in this habitat. No organic carbon stimulation was noted in the other sites. Salinity had little effect on ARA over the range generally experienced in each habitat.

Effect of nitrogen on the yield response of Pennisetum americanum, Triticum aestivum and Zea mays to inoculation with Azospirillum brasilense under temperate conditions

A nitrate-respiring strain, a denitrifying strain, and a non-nitrogen-fixing strain of Azospirillum brasilense were compared for their effect on the growth of pearl millet (Pennisetum americanum), wheat (Triticum aestivum) and maize (Zea mays) under temperate conditions in nitrogen-limited pot cultures. Increases in yield of Z. mays shoots occurred with all three strains when inoculation coincided with the addition of low levels of combined nitrogen. The inoculation of A. brasilense did not show any effect on the yield of P. americanum and T. aestivum. Increased numbers of A. brasilense became associated with Z. mays roots following the addition of low levels of combined nitrogen. Low and very variable rates of acetylene reduction activity were observed from excised roots of inoculated Z. mays plants without preincubation. Results indicate that inoculation of cereals with A. brasilense under temperate conditions has only a limited effect on plant growth.

Nitrogen fixation (C 2H 2 reduction) in a salt marsh: Its relationship to temperature and an evaluation of an in situ chamber technique

A temperature controlled chamber for the in situ measurement of nitrogen fixation (acetylene reduction) in a vegetated salt marsh is described. Rates of acetylene reduction activity (ARA) were linear during a 9 h incubation. Measurements of acetylene penetration into the sediment indicate that the chamber technique measures ARA within the top 2–4 cm of the sediment column. This depth of penetration accounted for approx. 60% of the total ARA in the sediment column. Measurements of in situ ARA in three zones of a vegetated salt marsh (tall, medium and short height Spartina alterniflora) over a year were positively correlated with seasonal temperature variations. About 70–80% of the seasonal variation in ARA was explained by the Arrhenius relationship: ARA ( μmol C 2H 4m −2h −1)= α exp(− β/ fT); where T is the ambient air temperature (°C) and α and β are constants. The constant α in this model increased from 20.1 to 40.5 while β increased from 17.5 to 20.7 along a transect from the tall to short height-form S. alterniflora communities. These differences suggest that there is spatial variability within the salt marsh among the variables that affect nitrogen fixation.

Acetylene Reduction Activity of Glycine max in Response to Inoculation, NPK Application, and Soil Environment

Soybean (Glycine max) was grown under natural greenhouse conditions in a non-sterile pot culture system, containing either perlite or soil. Sandy calcareous soil and chernozem soil, 4 levels of nitrogen (0.0, 40, 80, and 160 mg N kg−1 soil), 2 levels of phosphorus (0.0 and 80 mg P kg−1), and 2 levels of potassium (0.0 and 200 kg kg−1) were used. The net values of acetylene reduction activity (ARA) were calculated as the difference between inoculated and non-inoculated plants. 40 mg N kg−1 soil was found to be an optimum dose in addition to either P or K or both together for stimulating the ARA of soybean plants. Rates of ARA were closely related to soil environment and responded to NPK application. In einem Gewächshaus-Gefäßversuch wurde unter unsterilen Bedingungen die Azetylen-reduktions-Aktivität (ARA) von Soja-Pflanzen (Glycine max) untersucht. Krumenboden eines kalkhaltigen Sandes und einer Schwarzerde sowie Perlit erhielten eine Mineraldüngung in Form von 4 N-, 2 P- und 2 K-Stufen. Die Nettowerte der ARA wurden als Differenz zwischen beimpften und unbeimpften Pflanzen kalkuliert. 40 mg N/kg Boden als Ammonnitrat erwiesen sich in Verbindung mit P und/oder K als optimal für die Stimulierung der ARA von Sojapflanzen. Die ARA korreliert eng mit den Bodeneigenschaften und ist abhängig von der NPK-Düngung.

Evidence for NH4+ switch-off regulation of nitrogenase activity by bacteria in salt marsh sediments and roots of the grass Spartina alterniflora.

The regulatory effect of NH4+ on nitrogen fixation in a Spartina alterniflora salt marsh was examined. Acetylene reduction activity (ARA) measured in situ was only partially inhibited by NH4+ in both the light and dark after 2 h. In vitro analysis of bulk sediment divided into sediment particles, live and dead roots, and rhizomes showed that microbes associated with sediment and dead roots have a great potential for anaerobic C2H2 reduction, but only if amended with a carbon source such as mannose. Only live roots had significant rates of ARA without an added carbon source. In sediment, N2-fixing mannose enrichment cultures could be distinguished from those enriched by lactate in that only the latter were rapidly inhibited by NH4+. Ammonia also inhibited ARA in dead and live roots and in surface-sterilized roots. The rate of this inhibition appeared to be too rapid to be attributed to the repression and subsequent dilution of nitrogenase. The kinetic characteristics of this inhibition and its prevention in root-associated microbes by methionine sulfoximine are consistent with the NH4+ switch-off-switch-on mechanism of nitrogenase regulation.

Seasonal changes in rates of nitrogen-fixation (AR) and numbers of potential nitrogen-fixing bacteria associated with excised roots of aquatic angiosperms

Seasonal changes in nitrogen-fixation and numbers of potential nitrogen-fixing bacteria associated with excised roots of angiosperms from Balgavies Loch, a eutrophic loch in eastern Scotland, were studied by the acetylene reduction method. The acetylene reduction activity (ARA) and numbers of bacteria fluctuated seasonally in each plant and from one site to another. Significant rates of ARA were associated more with two C 3 grasses, Phalaris arundinacea L. and Phragmites australis (Cav.) Trin. than with the non-grasses, Juncus effusus L. and Polygonum amphibium L. Correlations were not always obtained between rates of ARA and numbers of nitrogen-fixing bacteria. Optimum pC 2H 2 for nitrogenase activity was variable. Thus, while a pC 2H 2 of 0.06 atm appeared adequate for Polygonum, the optimum for Phalaris seemed to lie somewhere between 0.10 and 0.15 atm. The rates of ARA of Phragmites and Juncus, on the other hand, increased with increases in pC 2H 2 between 0.01 and 0.20 atm. These increases were, however, very small, between 0.10 and 0.20 atm. As has been reported by other workers, the ARA of the angiosperms was both O 2 sensitive and O 2 dependent, with maximum rates being obtained at pO 2 between 0.01 and 0.05 atm. Lag periods of 3–5 h preceded the onset of the evolution of ethylene but these were eliminated by pre-incubating the samples for 6 h either in O 2 (pO 2 0.20 atm) or under anaerobic conditions. The ARA was depressed but not completely inhibited by ammonium and nitrate-nitrogen at concentrations of more than 2000 μg N l −1. This depression suggests that the acetylene reduction activity is by the nitrogenase enzyme system.

Effect of inoculation of Zea mays with Azospirillum brasilense strains under temperate conditions.

Seven strains of Azospirillum brasilense were compared for their effect on the growth of Zea mays grown under temperate conditions in sand--vermiculite pot cultures. Inoculation with all seven strains tested, including Fix(-) mutant strains, increased dry weight and total nitrogen content of shoots, but nitrogen concentrations were unaffected. Low and variable rates of acetylene reduction activity were observed from excised roots of inoculated plants without preincubation. Estimates of N2-fixing A. brasilense associated with inoculated roots showed differences between strains in establishing themselves in the rhizosphere and endorhizosphere. In some strains enrichment in the endorhizosphere of roots occurred following inoculation, but the relative numbers and location of the strains did not appear to affect the yield response.