In recently deglaciated soils, microbial organisms drive soil transformations by increasing carbon (C) and nitrogen (N) pools while depleting available phosphorous (P), thus improving plant colonization and soil development. However, the rate of soil development can vary in response to local environmental conditions that affect microbial abundance and activity. In this contribution we use observational and experimental approaches to evaluate the interplay between soil biogeochemical features and microbial abundance and function after approximately seventy years of soil development in the forefield of the Exploradores Glacier that is located at the northernmost end of the Northern Patagonian Ice Field. Our findings suggest that after approximately seventy years of soil development, microbial abundance and soil C and N accumulation increase with soil age, soil bulk density and pH decreased, and microbial activity measured as soil chlorophyll a and nifH gene abundance increased. In turn, decomposition increased with fungal abundance, showing higher values in the late stages of soil development where the soil C:N ratio was higher and soil pH was lower. Overall, biogeochemical changes along this chronosequence followed the predicted pattern, with gradual increases in soil nutrients and microbial abundance, in addition to decomposition processes.

Marine fog is a key non-rainfall water source that sustains microbial activity and transports dissolved nutrients inland, influencing early soil development in hyperarid ecosystems. However, the mechanisms through which sustained fog inputs drive soil surface modification and biocrust formation remain poorly understood. This study evaluated the effects of long-term fog augmentation on soil surface development, biocrust dynamics, and associated microbial communities in the Atacama Desert. We implemented a four-year fog addition field experiment with three sampling times (T0, T24, T48) to assess changes in soil physicochemical properties, biocrust composition, and the integrated multi-diversity of archaea, bacteria, fungi and protist. Sustained fog input transformed bare soils into biological soil crusts, particularly lichen- and moss-dominated stages. This transition was accompanied by increases in soil nitrogen, variations in organic matter accumulation, a shift from alkaline to near-neutral pH, and improvements in soil stability and water retention. Multi-diversity increased over time and was positively associated with ecosystem variables linked to water availability, structural stabilization, and decomposition. These functions, integrated into an ecosystem multifunctionality index, also increased under prolonged fog input, revealing a positive relationship between multifunctionality and multi-diversity. Overall, the results demonstrate that sustained fog input strongly enhances early soil surface development and biocrust establishment, highlighting the ecological importance of marine fog in shaping biodiversity and ecosystem functioning in hyperarid landscapes.

Understanding how microbial communities from hyperarid environments respond to sporadic water availability is crucial for predicting ecosystem responses to unpredicta-ble precipitation related to climate change. Here, we experimentally simulated a short-term precipitation pulse (50 mm) in soils from the hyperarid Atacama Desert to evaluate shifts in microbial community composition, diversity, and functional potential, as well as changes in soil physicochemical properties. Using a microcosm experiment with time-structured sampling and high-throughput amplicon sequencing, we found that changes in soil properties after precipitation do not significantly influence micro-bial community composition. However, carbon dynamics exhibit significant variation. Actinobacteria and Proteobacteria dominated bacterial communities, exhibiting func-tional stability over time, which suggests high resilience. In contrast, fungal communi-ties, primarily composed of Ascomycota, displayed greater temporal variation in both taxonomic and functional profiles, particularly during intermediate hydration stages. Notably, fungal functional richness increased despite a limited taxonomic change, in-dicating lower redundancy and, thus, potentially higher community fragility. Our findings highlight distinct microbial strategies for coping with hydration pulses in ex-treme drylands, underscoring the role of fungi in nutrient cycling, decomposition, and soil structure, while also revealing their increased vulnerability to environmental fluc-tuations. Our results reinforce the importance of microbial dynamics in maintaining ecosystem functioning in pulse-reserve systems under ongoing climatic changes.