Drylands cover more than 40% of the terrestrial surface, and their global extent and socioecological importance will increase in the future due to the forecasted increases in aridity driven by climate change. Despite the essential role of metallic micronutrients in life chemistry and ecosystem functioning, it is virtually unknown how their bioavailability changes along aridity gradients at the global scale. Here, we analysed soil total and available copper, iron, manganese and zinc in 143 drylands from all continents, except Antarctica, covering a broad range of aridity and soil conditions. We found that total and available micronutrient concentrations in dryland soils were low compared with averages commonly found in soils of natural and agricultural ecosystems globally. Aridity negatively affected the availability of all micronutrients evaluated, mainly indirectly by increasing soil pH and decreasing soil organic matter. Remarkably, the available Fe:Zn ratio decreased exponentially as the aridity increased, pointing to stoichiometric alterations. Our findings suggest that increased aridity conditions due to climate change will limit the availability of essential micronutrients for organisms, particularly iron and zinc, which together with other adverse effects (for example, reduced water availability) may pose serious threats to key ecological processes and services, such as food production, in drylands worldwide.
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We thank all members of the EPES-BIOCOM network for the collection of field data, and all members of the Maestre laboratory for help with data organization and management, as well as comments and discussions about this work. We also thank T. Sizmur, R. L. Chaney and J. Behlert for edits and comments on earlier versions of our manuscript. This work was funded by a 2018 Leonardo Grant for Researchers and Cultural Creators of the BBVA Foundation, and by the European Research Council (ERC grant agreements 242658 (BIOCOM) and 647038 (BIODESERT)). C.P. was supported by Marie Skłodowska-Curie grant agreement number 654132 (VULCAN). H.S. is supported by a Juan de la Cierva-Formación grant from Spanish Ministry of Economy and Competitiveness (FJCI-2015-26782).
Supplementary Figures 1–6, Supplementary Table 1, Supplementary References, Model Parameters and R code