Abstract
Beneficial soil-borne bacteria and fungi are central to the performance of most plants. Knowledge of beneficial microorganisms and the processes in topsoils that favour the association of beneficial organisms with plants allows us to better manage soils for higher productivity and environment sustainability. This review describes the main groups of symbiotic and free-living organisms and explores how they contribute to plant and soil health in managed and natural ecosystems. Many field studies have investigated the biodiversity, ecology and function of beneficial organisms in relation to root distribution in topsoils and land management practices. There is scant information however on whether beneficial bacteria and fungi can persist and enhance root function in subsoils. Opportunities for enhancing beneficial plant-microbe interactions in the subsoil deserve scrutiny particularly as crop productivity is becoming more dependent on subsoil moisture with declines in rainfall in many parts of the world.