Rhizobial ecology as affected by the soil environment

Abstract

In this paper we review the influence of various soil factors on the legume–Rhizobium symbiotic relationship. Abiotic factors such as extremes in soil pH (highly acidic or alkaline soils), salinity, tillage, high soil temperature and chemical residues, all of which can occur in crop and pasture systems in southern Australia, generally reduce populations of Rhizobium in the soil. Naturally occurring Rhizobium populations, although often found in high numbers, are generally poor in their ability to fix nitrogen and can compete strongly with introduced Rhizobium inoculant. The introduction of new legume genera as a continuing and essential part of change in farming systems usually requires the need to identify new and specific inoculant Rhizobium strains not found in the soil, but necessary for optimum nitrogen fixation. It is therefore necessary to characterise the specific requirements or limitations in the soil for establishing Rhizobium populations to ensure optimal nitrogen fixation following inoculation of legumes. The ability of the introduced Rhizobium to form effective nodules is rarely linked to a single soil attribute; therefore the study of rhizobial ecology requires an understanding of many soil and environmental factors. This paper reviews current knowledge of the influence of soil factors on rhizobial survival, the nodulation process, and nitrogen fixation by legumes.

The effect of soil carbon on symbiotic nitrogen fixation and symbioticRhizobiumpopulations in soil withTrifolium repensas host plant

“…The amount of fixed atmospheric N in T. repens plants in the high C soils was substantially lower. This will subsequently lead to senescence of many nodules and soil N content will increase by rhizodeposition (Keyser et al 1992, Slattery et al 2001). The possible reason for lower soil N content of low C soil is as a result of more plant energy being available for plant growth, rendering biomass production more efficient.…”

“…Success of inoculation is a direct response to the indigenous rhizobial population numbers (Thies et al 1991a). Rhizobia must be prevalent enough in the soil to ensure success in sustainability of legumes in the grass systems (Slattery et al 2001).…”

Test of local adaptation to biotic interactions and soil abiotic conditions in the ant-tended Chamaecrista fasciculata (Fabaceae)

“…Nevertheless, although soil conditions can be considered a temporally less variable selective force than biotic factors (given that environmental temporal variability favors plasticity; Scheiner 1993), plants growing on their native soil did not outperform nonnatives. It is important to mention that we did not consider the role soil biotic conditions might play in this study (e.g., levels of nitrogen-Wxing bacteria; Slattery et al 2001), and these also could inXuence plant Wtness measures and local adaptation. Finally, although not included in this study, we also measured EFN nectar volume production in the greenhouse for the same plants used in the soil source £ population-source experiment, and results showed no home advantage (i.e., plants growing on their native soil did not produce more nectar than nonnatives).…”

Variations in infectivity of indigenous rhizobial isolates of some soils in the rainforest zone of Nigeria

“…It has been asserted that high N or soil fertility prevents nodulation in plant (Amarger 2001;Datta et al 2011), and this may have affected the soil at Idi-Ayunre. Agronomic practices do influence rhizobial population, and planting of different types of legumes can result in multiplication and stimulation of Bradyrhizobial population (Palmer & Young 2000;Slattery et al 2001;Hardarson & Atkins 2003). The size of bradyrhizobia population was taken into cognizance because it is an indication and one of the precursors which throws light on the need to inoculate and predict response to inoculation (Turk et al 1993).…”

“…It is a natural process which involves soil inhabiting bacteria known as rhizobia, infecting the root of legumes, forming nodules and fixing N. Rhizobial population can be few or numerous in the soil depending on several factors which include location, soil properties, presence and types of host plant and history of field use (Slattery et al 2001;McInnes et al 2004). In agricultural systems, rhizobia in the soil are termed native or indigenous and are usually differentiated from the introduced ones.…”