Desert Pavements: Interactions with Pedogenic and Microbial Processes

• Applicants: Professorin Dr. Daniela Sauer; Professor Dr. Dirk Wagner
• Subject Area: Physical Geography
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 573188573

Desert pavements cover about 50% of arid land surfaces, controlling key landscape processes such as surface runoff and pedogenesis. Their clast layer provides habitats for microbial communities, while dust accumulation below the clasts drives a causal chain of hydrological, pedogenic, and microbial processes - with fundamental implications for desert ecosystems. Yet, little is known about the underlying mechanisms and feedbacks. Based on existing literature and own previous work, we developed the following hypotheses on that causal chain and potential feedbacks on desert pavements: (i) Desert pavements are effective dust traps. In the aeolian layer that accumulates below the clasts, a vesicular horizon develops that reduces rainwater infiltration rates, thus enhancing surface runoff, which results in an increased redistribution of water in the landscape towards depressions. (ii) In those moister depressions, pedogenesis and microbial activity are enhanced, whereby enhanced microbial activity further stimulates soil aggregate formation through the production of extracellular polymeric substances. (iii) Protection from intense UV light and heat below dense desert pavements leads to greater microbial abundance than under pavements with looser clast coverage and larger spaces between the clasts, where the solar radiation directly hits the soil. The increased spatial soil-moisture variability due to the lateral water redistribution across the landscape further enhances microbial diversity. (iv) The interplay between pedogenesis and microbial activity underneath a desert pavement leads to increased soil aggregate stability, which in turn enhances desert pavement stabilization. These hypotheses will be tested by systematically analyzing soil profiles under desert pavements with DENSE and LOOSE clast coverage, in CONVEX and CONCAVE positions, where also soil moisture and soil temperature will be continuously recorded over two years. Based on soil-chemical and soil-physical analyses in combination with micromorphological analysis of soils, we will characterize and quantify pedogenesis in these systematically selected landscape positions. Modern molecular biological analysis of the abundance and diversity of microbial communities in the same soil profiles will be based on DNA extraction, while functional analysis of the microbial community will be based on RNA extraction. These analyses will be complemented by two soil manipulation experiments in the laboratory, whereby in a first step, aggregate formation with/without microbes will be compared, and in a second step, the aggregates formed with/without microbes will be tested for their stabilizing effect of the soil against erosion. Through this combination of pedological/soil-hydrological and microbiological analyses, complemented by laboratory experiments, this project will lead to a new level of understanding of the ecologically crucial causal chains and potential feedbacks related to desert pavements.

• DFG Programme: Research Grants