Variation of Soil Microbial Communities within a Consociation Soil Map Unit and a Vegetative Transect through an Oak Motte

by Shawver, Sarah Elizabeth, M.S., TARLETON STATE UNIVERSITY, 2017, 110 pages; 10262708


Soil microorganisms drive biogeochemical cycling. Soil microbial communities differ based on pH, texture, organic carbon, and nutrients. Soil microbial diversity and abundance decrease with depth. Ashe juniper (Juniperus ashei) is encroaching on live oak (Quercus virginiana) savannas, which may alter soil microbial communities and the ability of soil to cycle nutrients. The objectives were to determine whether soil microbial communities differ across a soil map unit and with depth, and determine whether soil microbial communities differ under the canopies of Ashe juniper and live oak.

We sampled 10 sites in a field mapped as a Windthorst consociation. At each site, we dug a pit to parent material and sampled by genetic horizon, and four additional satellite surface samples were collected. In another field, we identified three transects of live oak, Ashe juniper, and grasses. At each transect, we collected four A horizon samples in four areas: under the oak canopy, under the overlapping canopies of oak and juniper, under the juniper canopy, and in the grasses.

We characterized soil pH, texture, CCE, nitrogen, phosphorous, and carbon. Microbial communities were analyzed using massively parallel DNA sequencing, and separated into OTUs based on 97% sequence similarity. We analyzed results through QIIME using Kruskal-Wallis ANOVA, Mann-Whitney U, and Spearman’s rank correlations.

Results showed homogenous soil properties across the Windthorst field. There were no differences in microbial communities within each site. Differences in four phyla and four OTUs were observed among sites. Three phyla and 21 OTUs varied with phosphorus. This suggests soil microbial communities have little variation over short distances, but have greater changes over greater distances. Prokaryotic communities likely change in response to changes in soil nutrients. Participation of many rare microbes as important nutrient cyclers will potentially be lost if soil samples are composited over a large area.

Results across the vegetative transect suggest prokaryotic community diversity differed with vegetation, while fungal community diversity did not. Trends in phyla and genera were mostly associated with vegetation, pH, and CCE, rather than nitrogen and texture. Many prokaryotic genera associated with soil properties were important nutrient cyclers. Many fungal genera associated with pH and vegetation were mycorrhizal fungi, suggesting a plant-specific relationship.

AdviserDonald G. McGahan
Source TypeThesis
SubjectsMicrobiology; Agriculture; Bioinformatics
Publication Number10262708

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