17Eukaryotic communities commonly display a positive relationship between biodiversity and 18 ecosystem function (BEF). Based on current studies, it remains uncertain to what extent these 19 findings extend to bacterial communities. An extrapolation from eukaryotic relationships would 20 predict there to be no BEF relationships for bacterial communities because they are generally 21 composed of an order of magnitude more taxa than the communities in most eukaryotic BEF 22 studies. Here, we sampled surface water of a freshwater, estuarine lake to evaluate BEF 23 relationships in bacterial communities across a natural productivity gradient. We assessed the 24 impact of habitat heterogeneity -an important factor influencing eukaryotic BEFs -on the 25 relationship between species richness, evenness, phylogenetic diversity, and heterotrophic 26 productivity by sampling co-occurring free-living (more homogenous) and particle-associated 27 (more heterogeneous) bacterial habitats. Diversity measures, and not environmental variables,
28were the best predictors of particles-associated heterotrophic production. There was a strong, 29 positive, linear relationship between particle-associated bacterial richness and heterotrophic 30 productivity that was strengthened when considering evenness. There were no observable BEF 31 trends in free-living bacterial communities. In contrast, per-capita but not community-wide 32 heterotrophic productivity increased across both habitats as communities were composed of taxa 33 that were more phylogenetically clustered. This association indicates that communities with 34 more phylogenetically related taxa have higher per-capita heterotrophic production than 35 communities of phylogenetically distantly related taxa. Our findings show that lake heterotrophic 36 bacterial productivity can be positively affected by evenness and richness, negatively by 37 phylogenetic diversity, and that BEF relationships are contingent on microhabitats. These results
38. CC-BY-NC 4.0 International license peer-reviewed) is the author/funder. It is made available under a The copyright holder for this preprint (which was not . http://dx.doi.org/10.1101/231688 doi: bioRxiv preprint first posted online Dec. 11, 2017; 3 provide a stepping stone to compare biodiversity-productivity theory developed for Eukarya to 39 bacterial ecosystems.
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