Rhizosphere Microbial Communication in Soil Nutrient Acquisition

Most of the upper layer of the earth’s terrestrial crust is or has been influenced by plant roots, so most soil is actually rhizosphere soil at one time or another. Through their physical, chemical, and biological interactions with the soil, roots play a major role in soil formation (Jenny, 1941) and soil function (Wardle et al., 2004). Microbes factor prominently in global nutrient and energy cycling, facilitating respiration of up to 40% of nonanthropomorphic CO2 into the atmosphere (Raich and Schlesinger, 1992). In the rhizosphere, microbial processes include exudation, water uptake, nutrient mobilization, soil organic matter (SOM) decomposition, and respiration (Lynch and Whipps, 1990). Most organic matter is derived from bacterially fixed nitrogen (N), making organic N the second largest store of nitrogen after N2 (Sylvia et al., 2005). Microbial activity converts Q1 this organic N to plant accessible N, eventually returning much of it to the atmosphere as N2, N2O, and even small amounts of NOx gases (Paul and Clark, 1996). Given that N-limited plants rely on microbial activities for acquisition of soil N, and that this exchange is mediated by carbon (C)-limited soil microbes through transfer of plant C, understanding microbial physiology and community function are critical to plant ecology and health in natural environments. This chapter will review the recent literature concerning bacterial community behaviors in relation to rhizosphere nutrient exchange, discussing first