Distinguishing Between the Impacts of Heat and Drought Stress on the Root Microbiome of Sorghum bicolor

Water deficit and extreme temperatures regularly and considerably reduce crop productivity. Although several studies have explored the role of the plant microbiome in drought tolerance, it remains to be determined how the often co-occurring factor of heat conjunctly shapes plant-microbe interactions. In order to compare the roles that temperature and drought stress play in plant microbial recruitment, we conducted a growth chamber experiment with a series of temperatures (22, 30, and 38 degrees C) and watering (drought versus watered) conditions in Sorghum bicolor, sampling soil mixtures and seedling roots at 7 and 21 days after initial stress initiation. We found that bacterial root communities had the lowest a diversity when under drought and at 38 degrees C, and that temperature influenced the b diversity of soil mixture and root microbiomes to a greater extent than watering treatment. Additionally, we observed that the relative abundances of members of phylum Actinobacteria increased both under drought and, incrementally, with higher temperatures. Furthermore, unique Actinobacteria were indicator species of either temperature or watered conditions, and indicators of high temperature in watered conditions were predominantly in the phylum Actinobacteria. Together, these data suggest that heat and drought stress differentially affect microbiome assembly in significant ways and unique Actinobacteria are recruited under either stress. This work informs our understandings of how abiotic stresses jointly shape crop microbiomes, as well as highlights the need for additional work to describe what mechanisms may be involved in host-mediated microbial recruitment and adaptation under various stresses in field-based studies.