Biodiversity is a major determinant of ecosystem functioning. Previous studies have found that primary production increases as terrestrial plant species richness increases in homogeneous conditions. However, what effect does biodiversity have on heterotrophic production for microbial ecosystems? Primary and heterotrophic production are highly correlated in lake ecosystems and studies have found that there is a relationship between phylogenetic diversity and productivity for active bacterial communities in homogeneous conditions. Therefore, we hypothesize with increased bacterial diversity there will be an increase in bacterial heterotrophic production, especially in heterogeneous particulate habitats that could be terrestrially, heterotrophically, or photosynthetically derived. To test our hypothesis, we performed seasonal and spatial sampling across a natural productivity gradient in a dynamic freshwater estuarine lake. We measured bacterial abundance by epifluorescence microscopy, bacterial community diversity of homogenous pelagic free-living and heterogeneous particulate bacterial communities via high throughput sequencing of the 16S rRNA gene, and secondary bacterial production by 3H-leucine incorporation into particle-associated and free-living bacteria. We calculated the bacterial richness, evenness, and abundance-unweighted mean pairwise phylogenetic distance as they compared to bacterial secondary production.
Results/Conclusions
While there was no trend with free-living bacterial (non-phylogenetic) diversity, there was a strong, positive, linear relationship between bacterial heterotrophic production and particle-associated bacterial richness and evenness, which was strongest for the inverse Simpson index (R2 = 0.69, p = 5x10-4). In contrast, there was a negative, linear correlation between abundance-unweighted phylogenetic diversity and heterotrophic productivity within both habitats, suggesting increased heterotrophic production in communities that are more phylogenetically clustered based on species presence-absence. Finally, there was a negative, linear correlation between species richness and unweighted phylogenetic diversity, signifying that as new species are added to the community these new species fall within phylogenetic groups already represented within the community. These results demonstrate a major contribution to how microbial diversity is linked to heterotrophic productivity in particulate habitats compared to free-living habitats, thus fitting microbes into macrobial theories about biodiversity-productivity relationships.