FrankiaAssemblages Associated withAlnus rubraandAlnus viridisAre Strongly Influenced by Host Species Identity

Abstract

This study examined the effect of host species identity on the structure of Alnus-associated Frankia bacterial assemblages in the Pacific Northwest, United States, using two approaches. First, Frankia in nodules were sampled from six stands of Alnus rubra or Alnus viridis. Second, a bioassay was conducted where A. rubra and A. viridis seedlings were grown in different soils collected from these two hosts. Frankia genotypes were characterized with nifH sequences and bacterial assemblages were compared using taxon- and divergence-based analyses. Strong host associations were evident in the field; the dominant Frankia genotypes showed significant associations with either A. rubra or A. viridis, and there were host-associated groupings at the assemblage level as well. In the bioassay, host associations among Frankia genotypes were evident but less pronounced, reflecting an interaction between host species and other factors. Although nodule abundance varied among bioassay treatments, seedling dry mass was not ...