UC Riverside

Abstract: Background and aims: 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 these microbial communities affecting natives’ abilities to compete with invaders. At the same time, climate change is leading to more frequent extreme wet and dry events. 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. Methods: 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 microbial shifts. Results: 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. Watering combined with invasion led to fewer shifts. Conclusion: 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. Graphical abstract: Understanding plant community response to global change drivers requires a comprehensive approach that assesses the relationship between plant competition and belowground rhizosphere microbial community responses. (a) In this work, we use a field experiment in a California grassland with a set of native forbs (purple) and invasive grasses (teal) to assess the combined effects of competition and water availability (drought, control, watered) on the rhizosphere microbiome. (b) Drought combined with competition from invaders altered the relative abundance of 36 functions (white) and 22 microbial families (blue) in the native rhizosphere compared to the effects of competition (3 functions, 16 families) or drought alone on natives (not shown: 5 functions, 0 families). (c) Additionally, regardless of watering treatment, invasive grasses sourced more of the taxonomic community in native-invasive mixes and this was exacerbated during drought. Overall, these results suggest invasion-driven shifts in the microbiome may be involved in weakening natives’ ability to cope with climate change, especially drought.