Interest has grown in developing rhizosphere microbiomes that promote crop growth in an effort to promote agricultural sustainability. However, doing so has proven to be difficult given the complexity of the soil environment. We sought to develop microbiomes associated with higher biomass production in Brassica rapa through directed evolution of whole rhizosphere microbiomes in a multi-generation experiment conducted in a growth chamber. Microbiomes were first derived from five different soils (i.e. vermicompost, organic farm soil, conventional farm soil, B. rapa conditioned soil, and a commercial biostimulant, ProBiota), then used to inoculate soils in a growth chamber. Plants were grown to maturity then harvested with rhizosphere soil. Soils from the four plants with the highest biomass in each treatment were selected and composited to formulate inoculants for subsequent generations. The selection process was repeated for five more generations. The second phase of the experiment tested the effects of plant host specificity, microbiome composition, and microbial transfer methods on biomass and seed yield.
Results/Conclusions
While selection for high aboveground biomass was not generated in this experiment, the results show that the initial microbial community impacts the trajectory of the plant biomass trait over the course of multiple plantings. Microbiomes derived from pre-conditioned B. rapa soils and from the commercial ProBiotic sources showed enhanced biomass yield over time, as compared to vermicompost microbiomes that showed inhibitive growth effects after six generations. These results, along with data from plant host and microbiome transfer methods, suggest that selection for whole plant-growth promoting rhizosphere microbiota are feasible.