Native Lespedeza species harbor greater non-rhizobial bacterial diversity in root nodules compared to the coexisting invader, L. cuneata

Abstract

Lespedeza cuneata is a non-native invasive legume that alters the soil bacterial community, associates promiscuously with rhizobia, and benefits more from rhizobial interactions compared to coexisting native Lespedeza in North America. We tested the hypothesis that native congeners differ in their nodule bacteria associations compared to L. cuneata. Plots with high L. cuneata invasion, low L. cuneata invasion with native Lespedeza species present, and uninvaded plots where native Lespedeza species existed without L. cuneata were sampled. Nodules were collected from all Lespedeza species present, and Chamaecrista fasciculata, a common native annual legume. Bacterial DNA from nodules was isolated and sequenced. Nodule bacterial composition differed significantly between hosts. L. cuneata nodules contained high frequencies of rhizobial DNA and low bacterial diversity, while native Lespedeza nodules contained lower rhizobial frequencies and higher non-rhizobial bacterial diversity. Specific non-rhizobial bacterial groups exhibited strong associations with native legumes and uninvaded sites. Significant differences exist in the nodule bacterial composition between native legumes and an introduced congener. The mechanism(s) and ecological importance of these differences remain unknown. These differences in bacterial associations could influence not only the competitive ability of the invader, but recovery of invaded sites as well.