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Abstract
Atmospheric CO2 concentrations are rising and have the potential to disrupt plant, soil, and microbial processes. In this dissertation we examined the effects of elevated CO2 (eCO2) on plant-microbe-soil interactions between two foundational desert plant species with different photosynthetic strategies: a C4 grass, Bouteloua eriopoda (black grama hereafter) and a C3 shrub, Larrea tridentata (creosotebush; creosote hereafter). We found that eCO2 impacted black grama and creosote from the rhizosphere to community level. eCO2 shifted root exudate composition, microbial community composition, and overall plant-soil feedback and competition dynamics between these species, shifting competition dynamics from exclusion towards neutrality. Additionally, soil organic matter (SOM) dynamics were affected, where eCO2 shifted SOM partitioning towards lower particulate (POM) vs. mineral-associated (MAOM) organic matter ratios. Structural equation modeling revealed root exudate diversity was negatively correlated with POM:MAOM and positively correlated with C:N, suggesting richer exudate profiles stimulated microbial activity that led to POM turnover. Overall, our findings expand on previous work by disentangling the mechanisms that drive plant-soil feedback and SOM dynamics, especially at eCO2.