PS 13-127 - Covariation of plant and soil microbial communities along a water availability gradient in a north American prairie ecosystem

Background/Question/Methods

Plant and soil microbial communities have major impacts on ecosystem functioning, but how strongly these communities covary and the relative importance of abiotic versus biotic drivers in structuring them are not well understood. Along a natural water availability gradient in two sandhills prairie sites in Nebraska, USA, we tested the hypothesis that covariation in the composition and biomass of plant and soil bacterial communities is driven by plant root traits and soil properties. Specifically, we addressed the following questions. (1) How strongly are plant and rhizosphere bacterial biomass and community structure correlated? (2) Are rhizosphere bacterial biomass and community structure more strongly determined by plant community structure, root traits, or soil properties? In three types of sandhills prairie habitats varying in soil moisture (ridge, swale, and meadow, in order of increasing water availability), we quantified aboveground biomass and plant community composition, and sampled soil properties, microbial biomass, and 16S amplicon sequences.

Results/Conclusions

Along the water availability gradient, microbial biomass was positively correlated with aboveground biomass and soil organic matter content. The meadow (wettest habitat) had the highest plant biomass and soil bacterial biomass, as expressed by both total and bacterial phospholipid fatty acid content. However, bacterial alpha diversity negatively correlated with bacterial biomass, and was only weakly correlated with plant alpha diversity. Nevertheless, for other dimensions of structure, above and belowground communities were strongly related. Plant and soil bacterial beta diversities were significantly correlated, and this relationship depended on soil properties and root traits. Specifically, dissimilarity between soil bacterial communities was greatest when plant communities and root traits, especially root diameter and tissue density, were most dissimilar. The variation in soil bacterial community structure explained purely by soil properties or plant communities or root traits were low, and most variation was explained by the interactions among these three predictors. Although above and belowground communities often covary along environmental gradients, our results suggest that this may not always be the case for all dimensions of community structure. In combination with soil properties, soil bacterial diversity and composition may be driven more by the belowground functional properties than by taxonomic composition of the plants.