Technical Staff Oak Ridge National Laboratory Knoxville, Tennessee
Body of Abstract: Bacillus are ubiquitous soil bacteria that can form beneficial mutualisms with plants, enhancing their growth. In agriculture, introducing Bacillus strains into soil as biofertilizer is a strategy to improve plant yields but we know little about the efficacy of these inoculations across plant species or their impact on the resident microbiome. Understanding the genetic aspects of these plant-microbe interactions is crucial for predicting plant yields and developing more productive crops with minimal effects on the surrounding ecosystem. To investigate how different Bacillus strains interact with genetically distinct plants, we conducted a greenhouse experiment using four Populus genotypes and five Bacillus strains. Over a 5-week study, we measured plant growth parameters and assessed the effects of microbial invaders on poplar microbiomes with amplicon sequencing of the bacterial and fungal communities in the soil, rhizosphere, leaves, and roots. B. subtilis strains increased leaf number in the F1 P. trichocarpa X P. deltoides hybrid genotype 7300 and stimulated stem growth rates (P < 0.001). Stomatal conductance, a key component of photosynthetic activity, varied significantly based on tree genotype and across Bacillus strain that was added (P = 0.006). The diversity of bacterial and archaeal rhizosphere microbiomes increased marginally with number of leaves (P = 0.07). Rhizosphere, leaf, and root microbial communities were influenced by plant genotype, Bacillus strain, photosynthetic efficiency, and plant growth rates. Soil microbial community composition differed between B. velezensis and B. subtilis inoculations. Overall, Bacillus inoculations in soil had varying effects on Populus physiology driven by genotypic identity and influenced the resident microbiomes. We found specific Bacillus strains could enhance plant productivity but were dependent on host tree genotype highlighting the role that both host and biofertilizer genetics may play in predicting plant yields and crop productivity.