Bioavailability of macro and micronutrients across global topsoils: Main drivers and global change impacts

Authors: OCHOA-HUESO, R - University Of Cadiz; DELGADO-BAQUERIZO, M - University Of Seville; RISCH, A - Swiss Federal Institute; ASHTON, L - University Of Hong Kong; Augustine, David; BELANGER, N - University Of Quebec; BRIDGHAM, S - University Of Oregon; BRITTON, A - The James Hutton Institute; CAMARERO, J - Spanish National Research Council; CORNELISSEN, G - Norweigian Geotechnical Institute; Liebig, Mark

Submitted to: Global Biogeochemical Cycles
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/23/2023
Publication Date: 6/20/2023
Citation: Ochoa-Hueso, R., Delgado-Baquerizo, M., Risch, A.C., Ashton, L., Augustine, D.J., Belanger, N., Bridgham, S., Britton, A.J., Camarero, J.J., Cornelissen, G., Liebig, M.A. 2023. Bioavailability of macro and micronutrients across global topsoils: Main drivers and global change impacts. Global Biogeochemical Cycles. 37. Article e2022GB007680. https://doi.org/10.1029/2022GB007680.
DOI: https://doi.org/10.1029/2022GB007680

Interpretive Summary: While scientists have measured the abundance of elements present in the Earth's crust, we know much less about the degree to which these elements occur in surface soils in forms that are available to plant roots and soil microbes. We assembled a world-wide database on topsoil chemical elements in which their availability to biological organisms was measured with a consistent methodology using soil probes that exchange elements with the soil solution. We found that the most bioavailable soil elements across Earth's lands were salt-forming ions consisting of calcium, magnesium, potassium, aluminum, sulfur and nitrogen. A separate, less abundant group of bioavailable elements consisted of iron, manganese, phosphorus, zinc, boron, copper and lead. Availability of these elements in soil solutions covaried predictably based on their atomic mass and ionization energy. The degree to which availability of an element deviated from the predictions was associated with either (1) unusual levels of uptake and release from living organisms, (2) anthropogenic climate change, or (3) agricultural activities. This study represents the first quantification of bioavailability of elements across the planet's topsoils.

Technical Abstract: Understanding the chemical composition of our planet’s crust was one of the biggest questions of the 20th century1. More than one-hundred years later, we know the overall abundance and chemical composition of the Earth’s crust2. However, the global patterns in the bioavailability and coupling of topsoil chemical elements remain largely undetermined despite their importance for the productivity and functioning of terrestrial ecosystems3,4. We buried approximately 100,000 ion exchange membranes across a representative range of terrestrial ecosystems worldwide to demonstrate that the most bioavailable soil elements across Earth’s ecosystems are salt-forming ions like calcium, magnesium, and potassium, followed by aluminum, sulfur, and nitrogen. A third group of elements is iron, manganese, phosphorus, zinc, boron, copper, and lead. Patterns of bioavailability were biome-dependent and were altered by human activities. Based on their co-occurrence patterns, soil elements were highly coupled across biomes, and this coupling was predictable by the fixed laws of physics, particularly atomic mass and the second ionization energy. Deviations from the predictable coupling-atomic mass pattern indicated reorganizational processes that were related to three main destabilizing external forces: (i) life-driven processes such as element uptake and release, (ii) anthropogenic global change effects, and (iii) agriculture. Our work has implications for understanding the biogeochemical links that define the functioning of our planet at different spatiotemporal scales.