Both soil properties and plant traits shape the diversity, composition and functions of plant-associated soil microbial communities. However, the relative influence of these factors is poorly understood, as are interactive effects between factors and the degree to which their influence varies among climate zones. Methods: To address this gap, we compared the diversity and composition of soil microbial communities associated with co-occurring C3 and C4 grasses from arid and mesic environments, and plant traits influencing them. Results: Climate emerged as the main determinant of plant traits and microbial community properties. Within each climatic region, above- and below-ground traits and soil properties differentially affected microbial community composition, and their relative influence varied among communities. In both mesic and arid environments aboveground traits related to quantity and quality of leaf litter (e.g., specific leaf area, leaf C content) and nutrient availability were the most influential variables for community composition. However, in arid regions, belowground traits (i.e., root tissue density and specific root area) significantly contributed to structure the eukaryotic community, supporting the role of roots as important driver of eukaryotic differentiation in constrained environments. Further, the presence of C4 plants in the arid region resulted in higher relative abundance of ciliate protists and higher recruitment of potentially beneficial microbial community members from green algae mediated by drought adaptation traits (e.g. decreased abundance of fine roots). Conclusions: Overall, our study revealed a differential response of microbial communities to environmental conditions, suggesting that soil microbial community composition is influenced by trade-offs between host adaptive traits across distinct climatic regions.

Raw sequences, OTU tables and metadata.