Namib Desert Soil Microbial Community Diversity, Assembly, and Function Along a Natural Xeric Gradient

Abstract

The hyperarid Namib desert is a coastal desert in southwestern Africa and one of the oldest and driest deserts on the planet. It is characterized by a west/east increasing precipitation gradient and by regular coastal fog events (extending up to 75 km inland) that can also provide soil moisture. In this study, we evaluated the role of this natural aridity and xeric gradient on edaphic microbial community structure and function in the Namib desert. A total of 80 individual soil samples were collected at 10-km intervals along a 190-km transect from the fog-dominated western coastal region to the eastern desert boundary. Seventeen physicochemical parameters were measured for each soil sample. Soil parameters reflected the three a priori defined climatic/xeric zones along the transect ("fog," "low rain," and "high rain"). Microbial community structures were characterized by terminal restriction fragment length polymorphism fingerprinting and shotgun metaviromics, and their functional capacities were determined by extracellular enzyme activity assays. Both microbial community structures and activities differed significantly between the three xeric zones. The deep sequencing of surface soil metavirome libraries also showed shifts in viral composition along the xeric transect. While bacterial community assembly was influenced by soil chemistry and stochasticity along the transect, variations in community "function" were apparently tuned by xeric stress.

Ancient landscapes of the Namib Desert harbor high levels of genetic variability and deeply divergent lineages for Collembola

“…In support of this finding, a study of the distribution of ant species across a similar Namib Desert transect identified greater species richness at inland sites, where mean annual rainfall and productivity was higher than at more coastal sites (Marsh, ). Furthermore, coastal soils have elevated levels of cations (Scola et al, ), indicative of high salinity, and many of our coastal samples did not contain springtails (see Supporting information Appendix ). The occurrence of dew within soils would also influence the availability of springtail habitat (Belnap & Lange, ).…”

“…In addition to aridity, other physical and chemical parameters within the gravel plains also vary with distance from the coast, generally corresponding with the xeric zones. Scola et al (2018) found significant differences (ANOVA, p < 0.05) between zones for 13 of 17 measured physical and chemical parameters, based on sampling of a 190 km longitudinal transect at 10-km intervals (n = 20 sites).…”

“…Limited moisture in the gravel plains is provided through marine fog events in the west and sporadic rain at higher elevations in the east, leaving a hyperarid area between 60 and 90 km from the coast (Eckardt et al, ). As such, the gravel plains can be categorized into three xeric zones (fog, arid, and rainfall; Figure ) occurring along a gradient from the coast to the Escarpment (~1,000 m asl) (Scola et al, ).…”

“…In addition to aridity, other physical and chemical parameters within the gravel plains also vary with distance from the coast, generally corresponding with the xeric zones. Scola et al () found significant differences (ANOVA, p < 0.05) between zones for 13 of 17 measured physical and chemical parameters, based on sampling of a 190 km longitudinal transect at 10‐km intervals ( n = 20 sites). For example, soils in the coastal fog zone contained higher levels of sodium, calcium, and potassium than soils in the arid and rainfall zones, whereas soils in the rainfall zone contained more organic matter and phosphorus.…”

“…Bacterial diversity was also significantly different between zones (PERMANOVA, p < 0.05; T‐RFLP analyses of 16S rRNA community fingerprints), and enzyme activity increased for sites further inland, suggesting that gradients in the cycling of carbon, nitrogen, and phosphorus may also exist. However, water was still identified as the most important driver of bacterial diversity and function (Scola et al, ), although in an Austrian dry grassland it was vegetation, soil temperature, and soil texture that were the strongest drivers of springtail community composition (Querner et al, ).…”