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Understanding the chemical composition of our planet's crust was one of the biggest questions of the 20th century. More than 100 years later, we are still far from understanding the global patterns in the bioavailability and spatial coupling of elements in topsoils worldwide, despite their importance for the productivity and functioning of terrestrial ecosystems. Here, we measured the bioavailability and coupling of thirteen macro‐ and micronutrients and phytotoxic elements in topsoils (3–8 cm) from a range of terrestrial ecosystems across all continents (∼10,000 observations) and in response to global change manipulations (∼5,000 observations). For this, we incubated between 1 and 4 pairs of anionic and cationic exchange membranes per site for a mean period of 53 days. The most bioavailable elements (Ca, Mg, and K) were also amongst the most abundant in the crust. Patterns of bioavailability were biome‐dependent and controlled by soil properties such as pH, organic matter content and texture, plant cover, and climate. However, global change simulations resulted in important alterations in the bioavailability of elements. Elements were highly coupled, and coupling was predictable by the atomic properties of elements, particularly mass, mass to charge ratio, and second ionization energy. Deviations from the predictable coupling‐atomic mass relationship were attributed to global change and agriculture. Our work illustrates the tight links between the bioavailability and coupling of topsoil elements and environmental context, human activities, and atomic properties of elements, thus deeply enhancing our integrated understanding of the biogeochemical connections that underlie the productivity and functioning of terrestrial ecosystems in a changing world. Globally, the most bioavailable elements (Ca, Mg, and K) are amongst the most abundant in the crust, but N is more abundant than predictedBioavailability was controlled by soil pH, organic matter content, texture, plant cover, and climate, and altered by global changeElements were highly spatially correlated (coupled), and coupling was predictable by the atomic properties of elements, particularly mass Globally, the most bioavailable elements (Ca, Mg, and K) are amongst the most abundant in the crust, but N is more abundant than predicted Bioavailability was controlled by soil pH, organic matter content, texture, plant cover, and climate, and altered by global change Elements were highly spatially correlated (coupled), and coupling was predictable by the atomic properties of elements, particularly mass

The effects of growing seedlings of red oak (Quercus rubra) and red ash (Fraxinus pennsylvanica) with Hoagland solutions containing five N-regimes, differing in the N-forms (NH4, NO3) and concentrations (High and Low), in relation to light intensity were investigated by the utilization of enzymatic markers of the N assimilation pathway, nitrate reductase (NR) and glutamine synthetase (GS). Red oak and red ash showed different patterns of N-assimilation. Red oak seedlings assimilated NO3 in low amounts in their roots and leaves, whereas red ash seedlings assimilated high amounts of NO3, mostly in the leaves. A significant amount of constitutive NR activity was found in red oak seedlings supplied with NH4 N-regime. This could be characteristic of a species adapted to soils that are poor in nitrogen. Root GS activity was lower in red oak seedlings than in red ash seedlings, indicating that the rate of NH4 assimilation differed in these two hardwood species. Low irradiance reduced growth of both hardwood species, but greatly affected the specific leaf area of red ash and reduced NO3 assimilation (when data are expressed per leaf area). Both species reacted similarly to N-regimes in terms of relative growth rate.

•Plastic mulch is rarely removed from tree plantations and agroforestry systems.•After 10 years, mulch increased tree growth but degraded riparian soil quality.•Mulch reduced soil carbon, nitrogen, organic matter, earthworms and fine roots.•Two to three times more soil nitrate was still observed in mulch vs. control plots.•Removing plastic mulch can improve ecosystem services provision in riparian buffers.