(157b) Understanding the Poplar Microbiome Structure in Response to Host Stress

Plant roots in the soil provide a rich carbon source through root exudates and organ turnover that attracts soil bacteria. The bacteria associated with plants are diverse, with thousands of unique bacteria measured as operational taxonomic units (OTUs) identified in natural samples. The associated bacteria can have beneficial effects on the host plant through nutrient acquisition, signaling and defense, and buffering of extreme environmental conditions. The plant microbiome has been shown to be dependent on host plant genotype, soil type, and environmental conditions. Given the importance of plants as feedstocks for food and energy, it is important to understand how the microbiome changes in response to natural stresses and how these changes may supplement the host response.

Using Populus trees as host plants, we investigated how abiotic stresses affect the host plant and belowground microbiome. Drought stress was implemented by watering plants at complete wilting to identify potential microbes that are beneficial in buffering the plant against drought. Drought plants were significantly reduced in overall growth, with extreme decreases in photosynthesis rate due to closed stomata especially at the lowest water conditions. The effects of drought on the host plant and environment significantly changed the endophytic microbiome relative to control, with increases in alpha and gamma proteobacteria. Only 15 of the top 20 OTUs were shared between control and drought plants, representing 73% and 65% of the total identified OTUs in the system, suggesting that drought microbiome is more diverse relative to controls. In parallel, a shade stress was induced by limiting light input to near the CO₂ compensation point, affecting carbon allocation and the chemical environment of the host, ultimately leading to changes in the microbiome. 16 OTUs were shared with the control top 20, representing 65% of the total diversity. 4 of the differential OTUs were different than what was observed in drought stress. The microbiome of shade and drought plants clustered together by principal coordinate analysis, suggesting a core microbiome that is enriched under host stress conditions. With this information we can begin to identify bacteria that are conserved in all Populus host growth conditions, as well as bacteria that enriched under specific environmental stresses. This research will lead to holistic understand of how the microbiome community functions to supplement the host phenotype.