Interactions among soil carbon cycling, desert shrubs, and microbial communities in a California Great Basin Desert

Across cold deserts C cycling is localized in shrub relative to interspace soils. However, little is known concerning interactions among soil C cycling, shrub belowground processes, and microbial community composition in these ecosystems. These interactions were investigated for soils beneath desert shrubs Artemisia tridentata, Sarcobatus vermiculatus, and Tetradymia tetrameres across a California cold desert dune chronosequence.; Distribution and stable isotopic values of three soil organic matter fractions were linked to C accumulation, humification, and mineralization. Accumulations of all fractions were evident after 85 years of dune development and were mainly localized in surface soils. Reflecting humification, depletion of 13C was greater in heavy fraction organic matter than in light fraction and dissolved organic C. Enhanced depletion of 13C in light fraction and dissolved organic C in shrub relative to interspace soils was associated with higher C and N mineralization, signifying more extensive humification in shrub microsites. Results demonstrate the utility of delta 13C in describing humification in desert soils and emphasize the importance of light fraction and dissolved organic C in rapid C cycling under shrubs.; Impacts of hydraulic redistribution via shrub roots on root litter decomposition were assessed in spring and summer. In summer, hydraulic redistribution created diel drying-rewetting cycles, but the presence of roots depressed mean soil water potential. Despite very negative soil water potentials in summer, hydraulic redistribution by A. tridentata and S. vermiculatus stimulated decomposition. The reverse was true in spring when hydraulic redistribution was nonexistent and roots depressed decomposition rates because of soil drying. These results provide the first evidence that hydraulic redistribution enhances decomposition in dry soils.; Shifts in soil microbial communities beneath shrubs were evaluated and related to 34 belowground characteristics. In surface compared to subsurface soils, microbial communities were specific to shrub species. Microbial community separation was associated with NH4+, NO3 -, phosphorus and chloride concentrations, and % silt. Distributions of Gram-positive bacteria and fungi distinguished shrub versus interspace soils while Actinobacteria and fungi highlighted community differences within shrub soils. This research demonstrates the importance of inorganic N availability and soil texture in influencing microbial community composition in this ecosystem.