Evaluation of nitrogen fixation by bacteria in association with roots of tropical grasses.

Sandy loam soil, with added glucose, was incubated anaerobically under N2 and subjected to repeated 1-h C2H2 reduction assays In the presence of 1% glucose the addition of 50 μg NH4+ −N/g or of 20 μg NO−3 N/g (untreated soil contained 12 μg NH+4−N and 710 μg NO−3-N/g) caused at least some suppression of nitrogenase activity Activity developed when the KCl-extractable soil inorganic nitrogen concentration dropped below 35 μg/g In the presence of 01 or 005% glucose the addition of 5 μg NH+4−N/g caused some suppression of nitrogenase activity However, activity developed when the soil NH4+-N concentration dropped below about 4 μg/g With 01% glucose and 5 μg added NO−2 N/g, activity did not develop until the soil NO−2 -N concentration dropped to zero Added NO−3 N was rapidly reduced and denitrified to NO−2- N, N2O-N and NH+4 N and furthermore caused some inhibition of CO2 evolution The data from NH4−-addition experiments are consistent with a nitrogenase repression/ derepression threshold of 4 and 35μg NH+4-N/g at 005 and 1% glucose concentrations, respectively The data from NO−2- and NO−3-addition experiments suggest a combination of repression and toxicity effects in the presence of added NO−3 N

Effect of ammonium-, nitrite- and nitrate nitrogen on anaerobic nitrogenase activity in soil

Under different moisture conditions, the concurrent processes of ammonification, nitrification, denitrification, and N2 fixation in soils treated with different levels of farmyard manure (FYM; 0, 1, 2, and 3% of soil dry weight) were analyzed. All the four processes occurred readily only under moisture conditions corresponding to 60% of maximum water-holding capacity (MWHC), and were stimulated by FYM application, whereby anaerobicity was induced by the marked increase of the respiration activity. At moisture levels higher or lower than 60% MWHC, some of the processes were suppressed. Denitrification was prevented when the MWHC was less than 60%, while the nitrification was suppressed at 100% MWHC and under flooded conditions. The application of 1% FYM resulted in a substantial decrease of the ratios of denitrification to N2 fixation, irrespective of the moisture levels, and the ratios increased with the increase of the levels of FYM. In each FYM application, the value of the ratio of denitrifica...

Concurrent observation of several processes of nitrogen metabolism in soil amended with organic materials

SUMMARY: Acetylene reduction by Beijerinckia indica in shaken liquid cultures increased with increase of pC2H2 up to 0·74 atm. Acetylene reduction was linear for at least 40 min. The oxygen partial pressure also affected activity with most acetylene reduction at a pO2 of 0·15 atm for liquid cultures grown in air.

Acetylene Reduction by Beijerinckia under Various Partial Pressures of Oxygen and Acetylene

Acetylene reduction was assayed on soil cores from 23 surface soils from 9 regions in eastern Austria. The highest N2 fixation rates were found in saline soils and in peatlands (39.1–951.9 nmol C2 H4 m−2 day−1). Nitrogen fixation was comparatively higher on grassland than on forest and field plots ranging from 1.3 to 207.6 nmol m−2 day−1. A large number of soil properties were measured and correlated with nitrogenase activity. Principal component analysis (PCA) revealed relationships between N2 fixation and soil texture and C:N ratio. Interactions of N2 fixation with nutrient availability. pH and humus content were demonstrated. Nitrogenase activity seemed to be unaffected by the combined N content and by the N mineralization potential of the investigated systems. Endogenous C2H4 production as determined with the CO-inhibition technique did not affect the experiments. The conversion factor for 15N fixation determined for peat is 5.4 and for saline soils it ranges from 2.1 to 2.8.

Non-symbiotic nitrogen fixation associated with temperate soils in relation to soil properties and vegetation.

Short-term incubation studies of non-symbiotic nitrogen fixation using acetylene as the substrate for nitrogenase were carried out on six soil samples collected from various locations in the Western State of Nigeria, and on one soil sample collected from Wisconsin, U.S.A. Unamended soils reduced a very small amount of acetylene but with added organic materials (5% organic matter, 2% glucose or sucrose) acetylene reduction became substantial and in one case was more than 30,000 times that in the unamended soil. In general, more acetylene was reduced in anaerobic than in aerobic soils. Two of the soils were tested for suppression of acetylene reduction by NH4+-N. With the addition of up to 100 ppm nitrogen as (NH4)2SO4 to the soils incubated with sucrose, no depression of acetylene reduction was observed in one soil while it was reduced by about half in the other.

An assessment of non-symbiotic nitrogen fixation in some Nigerian soils by the acetylene reduction technique

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An assessment of non-symbiotic nitrogen fixation in some Nigerian soils by the acetylene reduction technique