John Brockwell

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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.(More)
Inputs of biologically fixed nitrogen derived from the symbiotic relationship between legumes and their root-nodule bacteria into terrestrial ecosystems amount to at least 70 million metric tons per year. It is obvious that this enormous quantity will need to be augmented as the world's population increases and as the natural resources that supply(More)
The great Order Leguminosae seems to have had its origin in Upper Cretaceous (Gundersen, 1950) or Cretaceous times (Andrews, 1914). The symbiotic relationship between leguminous plants and their root-nodule bacteria, Rhi zob ium spp., evolved subsequently, but how and when is a matter in dispute (Norris, 1956; Parker, 1968). Suffice to say that the rhizobia(More)
BACKGROUND AND OBJECTIVES Interactions between plants and beneficial soil organisms (e.g. rhizobial bacteria, mycorrhizal fungi) are models for investigating the ecological impacts of such associations in plant communities, and the evolution and maintenance of variation in mutualisms (e.g. host specificity and the level of benefits provided). With(More)
A method for estimating the nitrogen-fixing capacity of a population of rhizobia resident in soil is presented. legume test plants, growing under microbiologically-controlled conditions in test tubes packed with a vermiculite substrate moistened with a nitrogen-free plant nutrient solution, are inoculated directly with a suspension of the soil under(More)
Genetic instability within strains of rhizobia maintained on laboratory media is well recognized, although rarely has the mutation been characterized. Variability within a strain introduced into the field is very difficult to recognise due to poor understanding of naturally-occurring populations of rhizobia. We have examined populations of Rhizobium(More)
Hydrogen (H2) is a by-product of the symbiotic nitrogen fixation (N2 fixation) between legumes and root-nodule bacteria (rhizobia). Some rhizobial strains have an uptake hydrogenase enzyme (commonly referred to as Hup+) that recycles H2 within the nodules. Other rhizobia, described as Hup−, do not have the enzyme and the H2 produced diffuses from the(More)
The effect of rice culture on changes in the number of a strain of soybean root-nodule bacteria, (Bradyrhizobium japonicum CB1809), already established in the soil by growing inoculated soybean crops, was investigated in transitional red-brown earth soils at two sites in south-western New South Wales. At the first site, 5.5 years elapsed between the harvest(More)
Six cultivars of lucerne (Medicago sativa L.) were grown in all possible combinations with eight strains of Rhizobium meliloti in order to assess genetic variation in symbiotic nitrogen fixation. Host genotype and Rhizobium genotype effects on nitrogen fixation were respectively 4.8% and 21.0% of total phenotypic variance. Genetic variation due to host(More)
Two field experiments on symbiotic nitrogen fixation by nodulated legumes are described, one relatively complex in design and the other very simple. An appraisal has been made of the feasibility of each experiment as a model for world-wide trials intended to provide data about the contribution to nitrogen fixation by useful legumes that can be made by(More)