Abstract Three newly selected strains of Cyclopia rhizobia together with an inoculant strain, which has never been tested in the field with adequate experimental design, was assessed under both nursery and field conditions for symbiotic performance. The three new test strains were initially selected for their superior Nz-fixing abilities under glasshouse conditions, and then evaluated in this study for field performance. Cyclopia subternata Vogel and Cyclopia genistoides (L.) R. Br., which have the potential for producing high quality honeybushtea, were used as host plants in both the nursery and field studies.The effect of seedling inoculation at the nursery level was also examined for the four test strains under nursery conditions. The inoculation of cuttings under nursery conditions produced.significant increases in shoot biomass, shoot %N and shoot N content. More specifically, inoculating C. subternata with strains UCT44b and UCT61a significantly increased shoot biomass and N content relative to strain PPRICI3. Strains UCT44b and UCT61a also showed better nodulation with C. subternata cuttings compared to strains UCHOa and PPRICI3. Field inoculation of Cyclopia increased all growth parameters relative to the uninoculated control, except for leaf %N. Cyclopia subternata inoculated with strains UCT44b, UCT40a and UCT61a produced significantly lower b15N values than the uninoculatedC. subternata reference plant. Using the 15N natural abundance method, C. subternata was estimated to be gaining about half of its N from Nz fixation, while C. genistoides obtained less than half of itsN from symbioticnutrition.

Abstract Data collated from around the world indicate that, for every tonne of shoot dry matter produced by crop legumes, the symbiotic relationship with rhizobia is responsible for fixing, on average on a whole plant basis (shoots and nodulated roots), the equivalent of 30-40 kg of nitrogen (N). Consequently, factors that directly influence legume growth (e.g. water and nutrient availability, disease incidence and pests) tend to be the main determinants of the amounts of N2 fixed. However, practices that either limit the presence of effective rhizobia in the soil (no inoculation, poor inoculant quality), increase soil concentrations of nitrate (excessive tillage, extended fallows, fertilizer N), or enhance competition for soil mineralN (intercropping legumes with cereals) can also be critical. Much of the N2 fixed by the legume is usually removed at harvest in high-protein seed so that the net residual contributions of fixed N to agricultural soils after the harvest of legume grain may be relatively small. Nonetheless, the inclusion of legumes in a cropping sequence generally improves the productivity of following crops. Whilesome of these rotational effects may be associated with improvements in availability ofN in soils, factors unrelated to N also play an important role. Recent results suggest that one such non-N benefit may be due to the impact on soil biology of hydrogen emitted from nodules as a by-product of'N, fixation.

Abstract Three newly selected strains of Cyclopia rhizobia together with an inoculant strain, which has never been tested in the field with adequate experimental design, was assessed under both nursery and field conditions for symbiotic performance. The three new test strains were initially selected for their superior Nz-fixing abilities under glasshouse conditions, and then evaluated in this study for field performance. Cyclopia subternata Vogel and Cyclopia genistoides (L.) R. Br., which have the potential for producing high quality honeybushtea, were used as host plants in both the nursery and field studies.The effect of seedling inoculation at the nursery level was also examined for the four test strains under nursery conditions. The inoculation of cuttings under nursery conditions produced.significant increases in shoot biomass, shoot %N and shoot N content. More specifically, inoculating C. subternata with strains UCT44b and UCT61a significantly increased shoot biomass and N content relative to strain PPRICI3. Strains UCT44b and UCT61a also showed better nodulation with C. subternata cuttings compared to strains UCHOa and PPRICI3. Field inoculation of Cyclopia increased all growth parameters relative to the uninoculated control, except for leaf %N. Cyclopia subternata inoculated with strains UCT44b, UCT40a and UCT61a produced significantly lower b15N values than the uninoculatedC. subternata reference plant. Using the 15N natural abundance method, C. subternata was estimated to be gaining about half of its N from Nz fixation, while C. genistoides obtained less than half of itsN from symbioticnutrition.

Abstract Data collated from around the world indicate that, for every tonne of shoot dry matter produced by crop legumes, the symbiotic relationship with rhizobia is responsible for fixing, on average on a whole plant basis (shoots and nodulated roots), the equivalent of 30-40 kg of nitrogen (N). Consequently, factors that directly influence legume growth (e.g. water and nutrient availability, disease incidence and pests) tend to be the main determinants of the amounts of N2 fixed. However, practices that either limit the presence of effective rhizobia in the soil (no inoculation, poor inoculant quality), increase soil concentrations of nitrate (excessive tillage, extended fallows, fertilizer N), or enhance competition for soil mineralN (intercropping legumes with cereals) can also be critical. Much of the N2 fixed by the legume is usually removed at harvest in high-protein seed so that the net residual contributions of fixed N to agricultural soils after the harvest of legume grain may be relatively small. Nonetheless, the inclusion of legumes in a cropping sequence generally improves the productivity of following crops. Whilesome of these rotational effects may be associated with improvements in availability ofN in soils, factors unrelated to N also play an important role. Recent results suggest that one such non-N benefit may be due to the impact on soil biology of hydrogen emitted from nodules as a by-product of'N, fixation.

No description available.

Several nitrogen fixers were isolated from the roots and rhizosphere of Quebec crops. Many of these nitrogen fixers were discarded when the production of N(,2)O in the presence of C(,2)H(,2), as a test for denitrifying ability, was included as a selected characteristic. Further characterization of the Nir('+) strains showed that they were Azospirillum lipoferum. / The cytochrome composition of Azospirillum brasilense (a denitrifier) grown under various conditions in a defined medium was investigated. Optical absorbance difference spectra of the particulate fraction of cells grown under aerated conditions indicated the presence of cytochromes of type b, c and a+a(,3). Under low aeration there was a quantitative increase in cytochromes b and c with a concomitant decrease in the a+a(,3)-type cytochrome. At high aeration, a CO spectrum indicated the possible participation of an o-type cytochrome. / At both high and low oxygen concentrations, the supernatant fraction revealed only one c-type cytochrome. Its abundance was increased at low oxygen concentrations. / Cytochrome spectra of anaerobically grown cells using different nitrogen oxides (NO(,3)('-), NO(,2)('-) and N(,2)O) as final electron acceptors revealed the presence of the different cytochromes involved in anaerobic respiration. The reduction of NO(,2)('-) was associated with the cytochrome cd (peak at 620 nm) found only in the supernatant fraction of NO(,2)('-)-grown cells. / Growth on NO(,3)('-) was characterized by a diauxic type of curve in which the first logarithmic phase corresponded to the reduction of NO(,3)('-). The second logarithmic phase corresponded to the reduction of NO(,2)('-). / Growth of Azospirillum brasilense with NO(,2)('-) and N(,2)O as final electron acceptor was possible only when a small amount of NO(,3)('-) was present initially. In contrast with other bacteria, growth of Azospirillum brasilense with tungstate instead of molybdate did not result in NO(,3)('-) reductase-deficient cells. / The NO(,2)('-) accumulation observed with NO(,3)('-)-grown cells possibly resulted from the different NO(,3)('-)- and N(,2)('-)-reductase specific activities. However, the longer lag in the NO(,2)('-) reduction when higher concentrations of NO(,3)('-) were used may be due to a direct effect of NO(,3)('-) on the synthesis or activity of the NO(,2)('-) reductase.

No description available.

The role of Beijerinckia spa and Klebsiella spp in stream litter decomposition was investigated using acetylene reduction method. Beijerinckia and Klebsiella were isolated during the winter and spring of 1980, from the leaves of sugar maple (Acer Saccharum), placed in Bell Creek, Muncie, Indiana. A nitrogen-free media was used to isolate Klebsiella. Both of these organisms were streaked separately on nitrogen-free agar slant tubes, flushed with argon and acetylene added. Gas chromatographic analysis were conducted on the innoculated tubes after incubation for 24 hours at 320 C. Beijerinckia spp, isolated from January, February, and April fixed between 4.48 x 10-7 moles and Klebsiella spp isolated during the same time period was between 1.47 to 8.10 x 10-8 moles. This study indicates that Beijerinckia is a better N2 fixer than Klebsiella in stream litter decomposition.

No description available.

No description available.