Assessing the relevance of an enhanced root growth due to the activity of rhizobacteria for plant phosporus uptake under low P supply

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Plant growth promoting rhizobacteria help plants to grow at sub-optimal P supply in different ways. They increase P availability in the rhizosphere and they can induce an enhanced root growth which enables plants to exploit larger soil volumes. The objective is to assess for an Enterobacter strain (E. radicincitans) which of these processes is of more importance. Root growth dynamics of maize will be determined in rhizoboxes which allow a daily view on the roots. Furthermore, root growth will also be quantified in field experiments at different P and inoculation levels. The ability of E. radicincitans to increase P soil solution concentration will be investigated in incubation studies with soils differing in their main P source. Additionally, a P fractionation of rhizosphere soil of incubated and non-incubated plants in comparison to bulk soil reveals which P form is mainly solved by E. radicincitans. Finally, all the data of the field, pot, and incubation experiments will be used for modelling sorption processes, soil transport, and uptake. This gives information about the relevance of enhanced root growth and/or P solubilization for a better plant growth at sub-optimal P supply.