Resource availability effects on prairie soil bacterial richness and diversity

Background/Question/Methods

Increases in the availability of a limiting resource can lead to decreases in species richness in plant communities, but limited work has explored this effect belowground. This project takes advantage of an ongoing long-term ecological research site to ask whether shifts in plant inputs and soil resource availability influences bacterial species richness and diversity. To investigate resource effects on species diversity, soil was collected from beneath sixteen monoculture plant species plots that differed in biomass production as well as variation in nutrient contents. DNA extracted from this soil was used to created 16S libraries. The generated sequence data was denoised prior to using the QIIME pipeline to generate richness and alpha diversity measures. All plant and soil measurements used were collected from publicly available LTER databases. One plant species plot had to be removed due to a low number of reads (<1000), possibly due to the extremely low amount of total plant biomass in that plot. Alpha-diversity measures were bootstrapped values based on subsets of 35,000 reads from all of the remaining plots.

Results/Conclusions

There were significant differences in bacterial species richness, but not diversity, between plant functional groups (p=0.00375 and p=0.0991, respectively). These differences could not be explained by variation in plant inputs. There were no significant relationships between either bacterial diversity or richness and measurements of aboveground plant input (as total aboveground C, total aboveground N, aboveground C:N, or total biomass in g/m^2). Similarly, there was no significant relationship between either bacterial diversity or richness and belowground plant inputs (total root biomass, root production, or root C:N). Additionally, the difference among plant functional groups could not be explained by variation in soil resources. There were no significant relationships between either bacterial diversity or species richness and soil C, N, or C:N from soil at any of four depths (0-10, 10-20, 20-40, or 40-60cm). Further, neither soil C flux or soil N flux (ammonification, nitrification, net mineralization) measurements were significantly related to bacterial diversity or species richness. We found no support for the idea that plant inputs or available soil resources influence soil bacterial diversity or species richness at the local scale within a prairie ecosystem; although these patterns may be evident at larger scales.