Invasive plant species interact with drought to shift key functions and families in the native rhizosphere

Interactions between species invasions and climate change have the potential to drive changes in plant communities more than either factor alone. One pathway through which these effects can occur is via changes to the rhizosphere microbial community. Invasive plants can alter the taxonomic and functional makeup of these microbial communities, which may affect natives' abilities to compete with invaders. At the same time, climate change is leading to more frequent extreme wet and dry events, shifting the composition of microbial taxa available in the soil. Understanding the response of plant communities to these combined global change drivers requires a comprehensive approach that assesses the relationship between plant competition and belowground rhizosphere microbial community responses. Here we use a field experiment in a California grassland with a set of six native annual forbs (i.e., wildflowers) and three invasive annual grasses to test how competition with invasive plants alters both identity and function in the native rhizosphere microbiome, and whether competition between these groups interacts with rainfall to amplify or ameliorate these microbial shifts. Metagenomics of rhizosphere communities revealed that drought combined with competition from invaders altered a higher number of functions and families in the native rhizosphere compared to invasive competition alone or drought alone. This suggests invasion-driven shifts in the microbial community may be involved in weakening natives' ability to cope with climate change, especially drought. Understanding the role of the microbial community under invasion and climate change may be critical to mitigating the negative effects of these interacting global change drivers on native communities. ### Competing Interest Statement The authors have declared no competing interest.