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Root-derived, labile organic compounds are thought to enter the rhizosphere food web mainly via consumption by mycorrhizal fungi and bacteria. Studies tracking the fate of root derived carbon via stable isotope probing (SIP), however, indicate an important role for saprotrophic fungi as consumers of root exudates. In addition, it was shown that a diverse group of rhizosphere bacteria have the ability to withdraw carbon from saprotrophic fungal hyphae. Based on the fast carbon-flow into saprotrophic rhizosphere fungi and the wide-spread occurrence of rhizosphere bacteria with mycophagous abilities, we argue that the current concept of rhizosphere carbon flow should be revised to account for more complex microbial food web interactions. We propose to split the bacteria thriving in the rhizosphere niche into “plant-feeders” and “fungus-feeders”. The latter would include rhizosphere bacteria feeding on all functional groups of fungi, i.e. including mycorrhiza. To indicate the importance of saprotrophic fungi as a food source for rhizosphere bacteria, we introduce a new niche, the “sapro-rhizosphere niche”. We want to stimulate a discussion on rhizosphere carbon flow by challenging the established division into a mere bacterial- and fungal channel consisting of primary consumers, and to point at research directions based on the sapro-rhizosphere concept. [ABSTRACT FROM AUTHOR]

The synergistic interaction between arbuscular mycorrhizal fungi (AMF) and phosphate solubilizing bacteria (PSB) can enhance growth and phosphorous uptake in plants. Since PSBs are well known hyphal colonizers we sought to understand this physical interaction and exploit it in order to design strategies for the application of a combined microbial inoculum. Phosphate-solubilizing bacteria strongly attached to the hyphae of Rhizoglomus irregulare were isolated using a two compartment system (root and hyphal compartments), which were separated by a nylon mesh through which AMF hyphae could pass but not plant roots. Allium ampeloprasum (Leek) was used as the host plant inoculated with R. irregulare. A total of 128 bacteria were isolated, of which 12 showed stable phosphate solubilizing activity. Finally, three bacteria belonging to the genus Pseudomonas showed the potential for inorganic and organic phosphate mobilization along with other plant growth promoting traits. These PSBs were further evaluated for their functional characteristics and their interaction with AMF. The impact of single or co-inoculations of the selected bacteria and AMF on Solanum lycopersicum was tested and we found that plants inoculated with the combination of fungus and bacteria had significantly higher plant biomass compared to single inoculations, indicating synergistic activities of the bacterial-fungal consortium. [ABSTRACT FROM AUTHOR]