Ecological genomics of mutualism decline in nitrogen-fixing bacteria

Mutualisms play key roles in natural and managed ecosystems, and these interactions are shifting in the face of anthropogenic changes. The evolutionaryeffects of global changes on mutualisms remain largely unaddressed. In the ecologically important legume-rhizobium symbiosis, rhizobial bacteria trade nitrogen for carbon, making this mutualismsensitive to changes in nitrogen availability. We used whole-genome sequencing to study the genetic differences between field rhizobium populations that either did, or did not, experience 22 years of nitrogen fertilization.