The effect of ammonium nitrogen on fixation of elemental nitrogen inAlnus andMyrica

Summary 1. A substantial formation of nodules occurred on plants ofAlnus glutinosa andMyrica gale grown in water culture with different levels of ammonium nitrogen labelled with N¹⁵ present in the culture solution. The nodules tended to be fewer but larger than on plants in solution free of combined nitrogen.2. The nodules continued to fix atmospheric nitrogen despite the presence of ammonium nitrogen in the rooting medium, though fixation per unit weight of nodule tissues formed was somewhat lower than in nitrogen-free solution. Among other possible reasons this could have been due to a substitution of ammonium nitrogen for elemental nitrogen at the nitrogen-fixing centres of the nodule, but evidently this does not occur to any great extent.3. In Alnus but not in Myrica fixation per plant was considerably enhanced in the presence of a low level of ammonium nitrogen, owing to greater nodule development. At higher ammonium levels, in excess of the plants' requirements, fixation per plant was still of comparable order to that in nitrogen-free solution, but now only represented some 24 to 45 per cent of the total nitrogen accumulated by the plants.4. The results suggest that under field conditions some fixation of atmospheric nitrogen will always be associated with nodules present.     

Effects of chemical modification of carboxyl groups in the hemolytic lectin CEL-III on its hemolytic and carbohydrate-binding activities

Effects of chemical modification of carboxyl groups in the hemolytic lectin CEL-III on its activities were investigated. When carboxyl groups were modified with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and glycine methyl ester, hemolytic activity of CEL-III decreased as the EDC concentration increased, accompanied by reduction of oligomerization ability and hemagglutinating activity. However, binding ability of CEL-III for immobilized lactose was retained fairly well after modification, suggesting that one of two carbohydrate-binding sites might be responsible for such inactivation of CEL-III.     

The effects of various chemical and physical haulm treatments on the incidence of potato gangrene

In studies of the influence of haulm defoliants on gangrene incidence in storage the use of diquat dibromide was consistently found to exacerbate levels of Phoma exigua vzr.foveata infection particularly on tubers harvested 3–4 wk after burning down. Intermediate levels occurred where the haulm was chemically defoliated with dinoseb or was physically cut and removed and least where the defoliants were sodium chlorate or sulphuric acid. Pycnidia of P. exigua var. foveata developed within 10 days on stems desiccated with diquat dibromide, sulphuric acid or dinoseb and most prolifically on those treated with diquat dibromide but tuber infection was not always related to their abundance. Speed of kill was not considered to be important in determining effect on gangrene incidence.     

The effect of water-logging on fixation of nitrogen by soil incubated with straw

Summary When straw was incubated with a calcareous soil under water-logged conditions nitrogen fixation occurred if the gas above the incubation contained oxygen: no detectable fixation occurred if oxygen was excluded. Moist soil failed to fix nitrogen when incubated with straw in either the presence or absence of oxygen.     

The effect of strA mutation on symbiotic nitrogen fixation by Rhizobium meliloti.

Studies on 3H-dihydrostreptomycin accumulation and binding to ribosomes showed that ineffective strain CMts17 carries strB type mutation changing its membrane permeability to the drug. Introduction of high level streptomycin resistance of strA type into strain CMts17 was correlated with acquisition of effectiveness and membrane permeability to the drug. This suggests that changes in membrane permeability, responsible for ineffectiveness of strain CMts17, can be reversed by strA mutation.     

Factors in the physical and biological environment affecting nodulation and nitrogen fixation by legumes

Summary The effects of root temperature on the four main stages of nodule formation and function are reviewed. Compared with results obtained under optimal conditions, lower root temperatures retard root hair infection more than they affect nodule initiation, nodule development (including bacteroid tissue development and degeneration), or nitrogen assimilation. Higher root temperatures upset the formation of bacteroid tissue and hasten its degeneration. Tropical and subtropical legumes have higher minimum temperatures for nodule formation than temperate species. Low and high shoot temperatures affect nodulation and nitrogen fixation, but the effect is less severe than that of similar root temperatures. Various approaches to minimise adverse environmental effects are considered. These include the selection of appropriate biological material (both host plants and bacterial strains) for the prevailing conditions, and the adoption of management practices designed to utilise the environment or to minimise its adverse effects. The importance of increase in bacteroid volume in relation to increase in rate of nitrogen fixation is considered, and the concept of compensation in nodule production and activity is examined. The limited information on defoliation effects on the nodulation of both temperate and tropical legumes is reviewed and aspects requiring examination are discussed.     

Minimizing the effect of mineral nitrogen on biological nitrogen fixation in common bean by increasing nutrient levels

Although common bean (Phaseolus vulgaris L.) has good potential for N₂ fixation, some additional N provided through fertilizer usually is required for a maximum yield. In this study the suppressive effect of N on nodulation and N₂ fixation was evaluated in an unfertile soil under greenhouse conditions with different levels of soil fertility (low=no P, K and S additions; medium = 50, 63 and 10 mg kg^–1 soil and high = 200, 256 and 40 mg kg^–1 soil, respectively) and combined with 5, 15, 60 and 120 mg N kg^–1 soil of ¹⁵N-labelled urea. The overall average nodule number and weight increased under high fertility levels. At low N applications, nitrogen had a synergistic effect on N₂ fixation, by stimulating nodule formation, nitrogenase activity and plant growth. At high fertility and at the highest N rate (120 mg kg^–1 soil), the stimulatory effect of N fertilizer on N₂ fixation was still observed, increasing the amounts of N₂ fixed from 88 up to 375 mg N plant^–1. These results indicate that a suitable balance of soil nutrients is essential to obtain high N₂ fixation rates and yield in common beans.