Microbial ecology of high elevation talus soils

The microbial ecology of unvegetated soils from a high elevation talus slope (3750 m) was investigated in Green Lakes Valley, Colorado Front Range. Talus slope soils are gravel and sand soils wedged among rocks, with a persistent thick snowpack. These cold, oligotrophic soils constitute extreme environments for microbial life. The description of microbial ecology had these goals: (1) to describe the N cycle and relationship between microbial biomass and soil physical factors in unvegetated and vegetated soils, (2) to understand how C availability and microclimate controlled seasonal patterns of microbial biomass, (3) to describe the roles of fungi and bacteria in the degradation of specific compounds, and (4) to describe the diversity of the overall microbial biomass and a specialized functional group.; The N cycling in unvegetated soils was similar to unvegetated and vegetated soils, with the same turnover times of inorganic N but much lower pools and rates. The microbial community structure was different in unvegetated than vegetated soil, with a greater proportion of salicylate mineralizers (SM) and weaker relationships between microbial biomass and soil factors. Seasonal trends in glutamate mineralizer (GM) biomass corresponded to the seasonality of C inputs in both soil types: biomass was highest during snowmelt when dust was deposited in unvegetated soils, and highest in winter and spring in vegetated soils while plants were senesced. In contrast, the SM biomass was highest in summer in both soil types. Niche partitioning occurred among fungi and bacteria in unvegetated soil. Proteobacteria were the most abundant Bacteria, while 6 other bacterial divisions represented a considerable breadth of diversity. The GM mineralizers included members of the gamma-, alpha-, and beta-Proteobacteria, as well as members of the Acidobacterium and Cytophaga/Flavobacterium/Bacterioides divisions. The GM are thus a mix of very phylogenetically distant groups, but they are a subset of the overall soil diversity. This study showed that despite being oligotrophic and cold, unvegetated soils at high elevations have complex microbial communities and processes.