Weathering and soil formation in hot, dry environments mediated by plant–microbe interactions

Abstract

Bioweathering in arid lands is a complex set of processes comprising a wide variety of organisms, all contributing to soil formation. Weathering starts with outcrop fragmentation by physical forces, later thermal stress and salts produce propagation of cracks that allow colonization by lithobiontic communities. Growth and development of primary colonizers produce pools of C and N available for further establishment of non-vascular plants when moisture is available. Furthermore, plants capable of living in crevices establish interactions with microbial communities and together optimize rock resources (organic or inorganic), enhance nutrient cycling, and accelerate soil development. Cacti and succulents are frequent rock colonizers in hot deserts. These plants exhibit numerous adaptations that enable them to survive in deserts including CAM biochemistry, physiological adaptations, and interactions with their associated microbiome. The associated microbiomes include plant growth-promoting microorganisms that increase essential nutrient supply (N and P) to the plants. We propose a conceptual model of weathering where microbial associates induce higher root exudation of organic acids in succulents. This model has to be experimentally tested; however, it involves several challenges, such as: (a) the difficulty of collecting exudates from the field or emulating experimental conditions similar to nature, and (b) selecting appropriate temporal scales to detect measurable changes since most cacti exhibit remarkably slow growth rates. Therefore, innovative approaches are in order.