Soil metabolomics reveals biocrust-mediated carbon and nutrient cycling in arid ecosystems

Biocrusts occur globally in ecosystems where plants are typically sparse, allowing sunlight to reach the soil surface, especially in natural drylands. Important ecosystem services have been attributed to them. Soil metabolomics is an emerging and powerful approach connecting soil chemistry, biology, and ecology. Understanding the role of biocrusts and their metabolic expressions is crucial for explaining how nutrient cycling adapts under arid conditions. Thus, in this study, a total of 56 plots, 20 m x 20 m in size, were surveyed in an arid natural area. For each plot, biocrusts and bulk soils (1-10 cm depth) were described through untargeted metabolomic analysis (LC−QTOF), and fertility properties. Multi and univariate approaches revealed both functional adaptation and spatial heterogeneity linked to biocrust development. A total of 59 differentially expressed metabolites (DEMs) were identified. Biocrusts concentrated a variety of metabolites related to intense biological activity and carbon and phosphorus cycling, as well as stress tolerance. Meanwhile, the bulk soils below serve as a reservoir for more persistent organic compounds and benefit from the nutrients and organic products released by the biocrust. Furthermore, the metabolomic fingerprints of the soils were found to be highly correlated with soil fertility properties. For example, our results reinforce the role of P (and Mn-associated processes) as key components of biocrust-driven biogeochemical cycling in arid soils. Definitely, this study demonstrates the power of untargeted metabolomics in revealing functional chemical expression and offers tools for managing the fertility of degraded soils by promoting healthy biocrusts.