The role of rhizosphere microorganisms in relation to P uptake by plants

The rhizosphere is defined as the soil around the roots that is influenced by the root (Hiltner 1904). Due to the release of easily decomposable compounds by the roots (root exudates), the rhizosphere is characterized by high microbial density. Rhizosphere microorganisms strongly influence nutrient uptake by plants by either enhancing or decreasing nutrient availability.

Rhizosphere microbial communities are a subset of the soil microbial community, but are often quite distinct from those in the bulk soil (Foster 1986; Marilley and Aragno 1999; Gomes et al. 2001; Berg et al. 2002). Rhizosphere communities are influenced by soil and plant factors. Soils can have distinct microbial communities (Gelsomino et al. 1999; Carelli et al. 2000), as a result of the soil physical and chemical characteristics (e.g. soil texture, nutrient and organic matter content and pH) and environmental factors such as climate and vegetation. Plants contribute to these physical and chemical properties by depositing between 1% and 25% of their net photosynthetic production, which includes dead roots, sloughed-off cells and soluble compounds (Merbach et al. 1999). A large proportion of the root exudates such as sugars, organic acid anions or amino acids are easily degradable by microorganisms in the rhizosphere resulting in high microbial density and activity in the rhizosphere (Foster 1986; Kandeler et al. 2001).