Jenny’s soil forming factors—time, parent material, climate, topography, and organisms—represent the major components to describe and quantify soil development. In almost all situations, it is difficult to hold even one of these factors constant when comparing sites. However, in our study site—the East and West side of a narrow North-South running ridge above timberline in SE Wyoming — three factors are nearly constant (time, parent material, and climate). The area was glacial scoured during the last major glacial period (~ 15,000 ybp) and the subsequent soil development has been relatively undisturbed by human impacts. The East side is the leeside of strong and prevailing westerly winds, receiving a large snow pack, while the West is consistently snow-free during winter creating very different moisture and soil temperature regimes. Our objective was to quantify the influence of topography/aspect on soil development and associated soil microbial communities on the two sides. Soil samples were taken for biochemical and isotopic analysis, including microbial community analysis using PLFA, and soil pits were used for soil classification. A seismic study was done to quantify the depth of soil/saprolite to bedrock.
Results/Conclusions
Both sides of the mountain ridge had a similar pH and generally low electrical conductivity, though the East side had a significantly higher EC. The two sides keyed out to the same soil family, with slightly different profile horizonation, and the East side showed an increase of clay with depth in the soil profile. The soil C:N ratios were similar, but the East side showed higher nitrates as well as higher organic matter (OM), which could be explained by the larger number of shrubs and forbs on the East side, while the West side had more mosses and lichens. A seismic study revealed that the depth of soil on the East side is approximately 30% deeper than on the West side. Both East and West showed high biomass of Actinomycetes and bacteria, followed by fungi and arbuscular mycorrhizal (AM) fungi, with the lowest biomass shown by protozoa. Bacteria, protozoa, and AM fungal biomass was slightly higher at the East side while fungal biomass was slightly higher on the West side. These multi-dimensional results from two very near-by sites adds to our understanding of fine-scale soil chemical, biological, and physical heterogeneity over a relatively short time of development.