Resistance of bacterial communities in the potato rhizosphere to disturbance and its application to agroecology

• Method for monitoring the relative impact of soils on rhizosphere microbiology.
• The first soil a plant encounters has the largest impact on rhizosphere microbiology.
• Modifying the bacterial community first encountered by a plant increased plant mass.

Soil bacteria have the ability to increase agricultural sustainability through the production of biopesticides and biofertilizers. Application of bacteria to field crops often results in sporadic colonization and unpredictable crop performance. This research sought to understand the colonization of the potato (Solanum tuberosum L.) rhizosphere using reciprocal transplants. Plants were grown in a forest or an agricultural soil and then transplanted into either the same soil or the opposite soil. Bacterial communities were profiled using terminal restriction fragment length polymorphism (TRFLP) and analyzed using pairwise comparisons. The results revealed that the bacterial community that colonized the rhizosphere in the first soil remained mostly intact for 30 days after the plants were transplanted into another soil in which the soil bacteria community differed from that found in the original soil. The concept that it may be possible to establish a functional microbiota and to deliver it to an agricultural environment was tested. A nitrogen-fixing bacterial community was established on plants grown under tissue culture conditions and the plants were transplanted into a field soil. Plants inoculated with eight separate nitrogen-fixing communities showed an average fivefold increase in dry biomass when compared to mock-inoculated plants and the microbial profiles remained distinct at 30 days after transplantation. These results demonstrate that the plant rhizosphere is a resistant community and that the first bacterial community that becomes established on the root remains with the plant even when the plant is placed into soil with a vastly different microbiota.