Trace gas oxidation supports sub-surface microbial communities across Namib Desert fog and aridity gradients.

UNLABELLED: Widely accepted climate predictions indicate that drylands will expand to cover more than half of the Earth's terrestrial surface by the end of the 21st century. In these environments, harsh conditions, including nutrient and water limitations, restrict plant and animal life, thereby increasing the importance of soil microbial communities in nutrient cycling and ecosystem functioning. The Namib Desert is a distinctive dryland ecosystem characterized by a steep natural aridity gradient, transitioning from a coastal hyperarid zone influenced by frequent fog deposition to an inland arid region receiving seasonal rainfall. This study investigates the impact of water availability and moisture regime on microbial trace gas oxidation and community composition across this aridity gradient. Quantitative analyses revealed that total microbial abundance and activity indicators, including ATP concentrations and respiration rates, were significantly (P < 0.005) reduced in hyperarid soils compared to their arid counterparts. In contrast, hyperarid fog-dominated soils exhibited significantly (P < 0.0005) elevated rates of atmospheric hydrogen oxidation, even in the absence of water inputs. We propose that sustained high-affinity hydrogen oxidation, coupled with rapid microbial resuscitation following wetting events, supports shallow sub-surface microbial communities in the Namib Desert, particularly in the coastal hyperarid zone. Together, these findings challenge current understanding of the lower limits of microbial activity and reveal alternative metabolic pathways that enable microbial persistence in hyperarid hot desert soils.

IMPORTANCE: Drylands are expanding globally, yet the mechanisms that allow microbial life to persist under extreme and sustained water limitation remain poorly understood. This study demonstrates that atmospheric trace gas oxidation, particularly high-affinity hydrogen oxidation, supports active and resilient microbial communities in hyperarid soils of the Namib Desert, even in the absence of liquid water inputs. By revealing how microbes may couple trace gas metabolism to energy and water generation, our findings provide new insight into the lower limits of microbial activity in dry, hot desert soils and highlight the need to investigate how microbes persist and sustain soil ecosystem functioning.