Relationship between presence of the desert shrub Haloxylon ammodendron and microbial communities in two soils with contrasting textures

Shrubs are usually dominated species for desert ecosystems, and resource islands often occurred around shrubs. It is widely considered that soils beneath shrub canopy have higher microbial diversity and biomass than those outside of the canopy. However, it remains poorly understood how shrubs affect this resource islands along soil profile and functional consequence on soil microbial community changes. Here, we showed distinct patterns of soil physiochemical properties and microbial communities along a soil profile outward from the taproot of Haloxylon ammodendron (C.A. Mey.) in two soils with contrasting textures: Torripsamments and Haplocalcids (USDA Soil Taxonomy). Soil samples were collected in circles with radii of 5, 40, 100 and 200 cm respectively around the taproot in four randomly selected horizontal directions, and from respective depths of 0-20, 20-60 and 60-100 cm. Microbial biomass and community composition were examined using a chloroform fumigation extraction and phospholipid fatty acids method. Redundancy analysis showed that the spatial variability of soil microbial communities was closely correlated with that of soil water and nutrients in both soils. Soil microbial biomass, soil water and nutrient contents had a similar decreasing trend along the increasing distance from the taproot. The coarse-textured Torripsamments showed stronger variability of soil water and nutrient contents than the fine-textured Haplocacids within the resource islands, and similar results were observed for soil microbial biomass. A clear trend of spatial variability (outward from taproot) for various microbial groups was observed in Torripsamments, but not in Haplocalcids. The biomass decreased to a lesser extent for total fungi than bacteria, and for Gram-positive than Gram-negative bacteria in Torripsamments. Our results suggest that the presence of H. ammodendron plays an important role in shaping the spatial variability of microbial communities in these desert ecosystems. Soil texture may determine the intensity of their spatial variability. (C) 2016 Elsevier B.V. All rights reserved.