Water Vapor Adsorption Provides Daily, Sustainable Water to Soils of the Hyperarid Atacama Desert.

Water is necessary for all life on Earth. Water is so critical that organisms have developed strategies to survive in hyperarid environments. These regions with extremely low water availability are also unique analogs in which to study the physico-chemical conditions of extraterrestrial environments such as Mars. We have identified a daily, sustainable cycle of water vapor adsorption (WVA) and desorption that measurably affects soil water content (SWC) in the hyperarid region of the Atacama Desert in southern Perú. We pair field-based soil temperature and relative humidity soil profiles with laboratory simulations to provide evidence for a daily WVA cycle. Using our WVA model, we estimate that one adsorptive period-one night-increases SWC by 0.2-0.3 mg/g of soil (∼30 µm rainfall). We can plausibly rule out other water inputs during our field campaign that could account for this water input, and we provide evidence that this WVA cycle is driven by solar heating and maintained by atmospheric water vapor. The WVA may also serve to retain water from infrequent rain events in these soils. If the water provided by WVA in these soils is bioavailable, it could have significant implications for the microorganisms that are endemic to hyperarid environments.

Determination of low bacterial concentrations in hyperarid Atacama soils: comparison of biochemical and microscopy methods with real-time quantitative PCR.

Hyperarid Atacama soils are reported to contain significantly reduced numbers of microbes per gram of soil relative to soils from other environments. Molecular methods have been used to evaluate microbial populations in hyperarid Atacama soils; however, conflicting results across the various studies, possibly caused by this low number of microorganisms and consequent biomass, suggest that knowledge of expected DNA concentrations in these soils becomes important to interpreting data from any method regarding microbial concentrations and diversity. In this paper we compare the number of bacteria per gram of Atacama Desert soils determined by real-time quantitative polymerase chain reaction with the number of bacteria estimated by the standard methods of phospholipids fatty acid analysis, adenine composition (determined by liquid chromatography - time-of-flight mass spectrometry), and SYBR-green microscopy. The number determined by real-time quantitative polymerase chain reaction as implemented in this study was several orders of magnitude lower than that determined by the other three methods and probably underestimates the concentrations of soil bacteria, most likely because of soil binding during the DNA extraction methods. However, the other methods very possibly overestimate the bacteria concentrations owing to desiccated, intact organisms, which would stain positive in microscopy and preserve both adenine and phospholipid fatty acid for the other methods.