Because genotypes within a species commonly differ in traits that influence other species, whole communities, or even ecosystem functions, evolutionary change within one key species may affect community and ecosystem processes. Here we use experimental mesocosms to test how the evolution of reduced cooperation in rhizobium mutualists in response to 20 years of nitrogen fertilization compares to the effects of rhizobium abundance on soil nitrogen availability and plant community composition and diversity. The evolution of reduced rhizobium cooperation caused reductions in soil nitrogen that were as strong, or even stronger, than substantially reducing rhizobium mutualist abundance in a community. Effects of both rhizobium evolution and rhizobium inoculation on legume dominance, plant community composition, and plant species diversity were much smaller in magnitude, but suggest that rhizobium evolution can alter the relative abundance of plant functional groups. Our findings indicate that the consequences of rapid microbial evolution for ecosystems and communities can rival the effects resulting from the presence or abundance of keystone mutualists.

We conducted a greenhouse experiment manipulating rhizobium evolutionary history (rhizobia isolated from long-term nitrogen addition treatments or adajacent control plots) and rhizobium abundance (uninoculated) on experimental mesocosms simulating early successional plant communities. Data was originally collected on hard copy datasheets, was entered into spreadsheets, and proofed for errors. A number of values in the accompanying data files are calculations based on raw data (e.g., diversity indices), but the data has not otherwise been modified.

This dataset includes a number of files:

1) A ReadMe file that introduces the dataset and provides more detailed explanations for each column header

2) SAS code that describes the statistical analyses presented in the main text and in Tables S1-S8.

3) R code that can be used to reproduce the figures in the main text.

4) The plant growth, foliar nutrient content, and soil nitrogen data.

Within the data file, missing values are indicated by n/a.