Soil micronutrients are capital for the delivery of ecosystem functioning and food provision worldwide. Yet, despite their importance, the global biogeography and ecological drivers of soil micronutrients remain virtually unknown, limiting our capacity to anticipate abrupt unexpected changes in soil micronutrients in the face of climate change. Here, we analyzed >1300 topsoil samples to examine the global distribution of six metallic micronutrients (Cu, Fe, Mn, Zn, Co and Ni) across all continents, climates and vegetation types.

We found that warmer arid and tropical ecosystems, present in the least developed countries, sustain the lowest contents of multiple soil micronutrients. We further provide evidence that temperature increases may potentially result in abrupt and simultaneous reductions in the content of multiple soil micronutrients when a temperature threshold of 12–14°C is crossed, which may be occurring on 3% of the planet over the next century.

Altogether, our findings provide fundamental understanding of the global distribution of soil micronutrients, with direct implications for the maintenance of ecosystem functioning, rangeland management and food production in the warmest and poorest regions of the planet. Our global survey reveals consistent patterns of metallic micronutrients across global soils. We identified striking consistencies in the distribution of different micronutrients, which are less abundant in warmer arid and tropical soils closer to the equator. A global temperature threshold appears to govern the content of micronutrients in soils, dividing the world in two distinct micronutrient regimes through a clear climatic boundary that negatively influences the content of micronutrients in warmer ecosystems and suggests potential future exacerbation of micronutrient limitations in a warmer world.

This work further highlights the fundamental importance of conserving soil micronutrients particularly in least developed countries where many regions are already co-limited by multiple nutrients that ultimately determine ecosystem processes and food production. (Eduardo Moreno-Jiménez, Fernando T. Maestre, Maren Flagmeier, Emilio Guirado, Miguel Berdugo, Felipe Bastida, Marina Dacal, Paloma Díaz-Martínez, Raúl Ochoa-Hueso, César Plaza, Matthias C. Rillig, Thomas W. Crowther, Manuel Delgado-Baquerizo -authors)