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High CO2 has been shown to increase plant growth and to affect symbiotic activity in many legumes species, including soybean ( Glycine max [L.] Merr.). In order to assess the interaction between elevated CO2 and rhizobial symbionts on soybean growth and nodulation, we combined the effects of CO2 with those of different bradyrhizobial strains and methods of inoculation. Soybean seeds were sown in agricultural soil in pots and inoculated with three strains of Bradyrhizobium japonicum (5Sc2 and 12NS14 indigenous to Quebec soils, and 532c, a reference strain), the inoculum being either applied directly to the seed or incorporated into the soil. Plants were grown in growth chambers (22/17ºC) for 6 weeks, under either near ambient (400 μmol mol−1) or elevated (800 μmol mol−1) concentrations of CO2. Elevated CO2 increased mass (63%) and number (50%) of soybean nodules, particularly medium and large, allowed a deeper nodule development, and increased shoot dry weight (+30%), shoot C uptake (+33%) and shoot N uptake (+78%), compared to ambient CO2. The two indigenous strains induced more medium and large nodules under elevated CO2 than the reference strain and showed the greatest increases in shoot dry weight. Soil inoculation induced higher number of small nodules than seed inoculation, specifically for the two indigenous strains, but did not affect plant growth parameters. We conclude that soybean yield enhancements due to elevated CO2 are associated with the production of large and medium-size nodules and a deep nodulation, that the two indigenous strains better respond to elevated CO2 than the reference strain, and that the method of inoculation has little influence on this response. [ABSTRACT FROM AUTHOR]

Fatty acid composition was determined in cells of strains CBh5 and CBp7 of Rhizobium leguminosarum bv. viciae grown at four temperatures (10, 15, 22 and 30°C), and in bacteroids and nodules formed with faba bean (Vicia faba L.) grown at two day/night temperature regimes (22/15 and 15/10°C). Growth temperature markedly affected the fatty acid composition of free-living bacteria in both strains studied, and both showed similar variations at each temperature. The proportion of unsaturated fatty acids increased significantly with lowering of temperature. The major fatty acid found in bacteria and bacteroids was cis-vaccenic (C18: 1Δ11), which comprised up to c. 78 (bacteria) and 56% (bacteroids) of total fatty acids. The presence of polyunsaturated fatty acids (linoleic (C18 :Δ9, 12) and linolenic (C18 : 3Δ9, 12, 15) acids) was noted only in bacteroids, indicating changes following the differentiation of bacteria into bacteroids in the nodules. The fatty acid composition of nodules was similar to that of bacteroids, although major differences were found in their proportions. The different day/night temperature regimes had contrasting effects in bacteroids and in nodules. In bacteroids of both strains, the proportions of stearic (C18 : 0) and linoleic (C18 :Δ9, 12) acids decreased at the lower temperature regime. In nodules, the proportion of stearic 1C18 : 0) acid decreased, while that of linolenic (C18 : 3Δ9, 12, 15) acid increased at the lower temperature regime. However, those of cis-vaccenic (C18 : 1Δ11), linoleic (C18 : Δ9, 12) and palmitic (C16 : 0) acids increased or decreased depending on the rhizobial strain. The proportion of unsaturated fatty acids increased with the lowering of temperatures in bacteroids of both strains, and varied in whole nodules depending on the strain. Strain GBp7 showed a greater symbiotic efficiency (dry matter yield) than strain CBh5 under both temperature regimes. but no relationship was found with the proportion of unsaturated fatty acids of bacteria, bacteroids or nodules. [ABSTRACT FROM AUTHOR]

Dicarboxylic acid transport mutants of Rhizobium species are usually deficient in their ability to fix atmospheric dinitrogen. We report here a study comparing the physiology of root nodules on Phaseolus vulgaris L. cv Goldie induced by an effective strain of Rhizobium leguminosarum biovar phaseoli and a C4-dicarboxylic acid utilization mutant The mutant, while able to form nodules, was ineffective in N2 fixation. Carbohydrates and organic acids of roots and nodules formed by the 2 strains were monitored at 3-day intervals from 13 to 34 days after inoculation. Both carbohydrates and organic acids accumulated in ineffective nodules in comparison with the effective nodules The concentration of malic acid was tenfold higher in ineffective nodules than in effective nodules Other organic acids, i.e , lactate, malonate, ascorbate and gluconate, were also detected. Lactate and ascorbate were the only other organic acids accumulating in ineffective nodules The most prevalent carbohydrates found in both types of nodules were sucrose, glucose and fructose. Myo-inositol was the only cyclitol detected in both types of nodules. Carbohydrates and organic acids were present in lower concentration in roots than innodules, except for lactate. These compounds were not consistently detected in higher concentration in roots from plants inoculated with the mutant strain, as was the case in nodules. [ABSTRACT FROM AUTHOR]

Abstract: Knowledge of the microbiology of dinitrogen (N2)-fixing bacteria in compost rich in de-inking paper sludge (DPS) is limited. Dinitrogen (N2)-fixing bacteria from DPS composts were isolated and studied for their N2-fixing activity in vitro and in vivo. Two Gram-negative N2-fixing isolates were identified as Pseudomonas. At 20°C, both isolates revealed that N2-fixing activity was higher than that of three arctic Pseudomonas strains. Their N2-fixing activity was found to occur between 18 and 25°C, a pattern that was similar to the reference isolate Azotobacter ATCC 7486. Composts successfully showed N2-fixing activity after carbohydrate amendments both with and without inoculation of a N2-fixing isolate. These results suggest that DPS composts support N2-fixing bacteria and that N2-fixing activity is dependent on a usable carbohydrate source. [Copyright &y& Elsevier]