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14 páginas.- 6 figuras.- 53 referencias, 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., We acknowledge the following people as additional data contributors: Drs. G. Blume-Werry, V. Bruckman, J. Buss, S. Collins, E. Dorrepaal, K.N. Egger, J. Fridley, Gibson-Roy, R. Harrison, J. Heberling, K. Helsen, E. Hinman, A. K olstad, N. Lemoine, M. Lesser, E. Li, S. E. Macdonald, E. Mallory, E. Massicotte, H.B. Massicotte, T. Moore, C. Morris, L. Nijs, M. Smith, Suojala-Ahlfors, E. Thiffault, K. Trepanier, R. Uusitalo, L. Van Langenhove, S. Vicca, F. Wang, M. Werner, K. White and S. Wilson. R.O.H. was funded by the Ramón y Cajal program of the MICINN (RYC-2017 22032), by the R&D Project of the Ministry of Science and Innovation PID2019-106004RA-I00 funded by MCIN/AEI/10.13039/501100011033, by the program José Castillejo” of the “Ministry of Universities” (CAS21/00125), by a project of the European Regional Development Fund (FEDER) and the Ministry of Economic Transformation, Industry, Knowledge and Universities of the Junta de Andalucía (ERDF Andalucía 2014–2020 Thematic objective “01—Reinforcement of research, technological development and innovation”): P20_00323 (FUTURE-VINES), by the European Agricultural Fund for Rural Development (EAFRD) through the “Aid to operational groups of the European Association of Innovation (AEI) in terms of agricultural productivity and sustainability,” Reference: GOPC-CA-20-0001, and from Fundación Biodiversidad (SOILBIO). M.D-B. was supported by a Ramón y Cajal Grant (RYC2018-025483-I), a project from the Spanish Ministry of Science and Innovation (PID2020-115813RA-I00), and a project PAIDI 2020 from the Junta de Andalucía (P20_00879). JP acknowl-edges funding from MICINN (RYC–2021–033454). S. Bridgham and P. Reed were supported from National Science Foundation Macrosystems Biology Grant 1340847. KVS acknowledges support from the Belgian American Educational Foundation (Paul Vernel Fellow), the Fulbright Program and the Fund for Scientific Research-Flanders. J. Pergl and M. Vítková were partly supported by 17-19025S, EXPRO Grant 19-28807X (Czech Science Foundation), BiodivClim Call 2019 (Grant TACR SS70010001) and long-term research development project RVO 67985939 (Czech Academy of Sciences). Natasja van Gestel was funded by the National Science Foundation Grant 1643871. Stevan Earl was partially supported by the National Science Foundation under Grant DEB-2224662, Central Arizona-Phoenix Long-Term Ecological Research Program (CAP LTER). Lilia Serrano-Grijalva has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 890874. Kevin van Sundert acknowledges support from the Fund for Scientific Research-Flanders. Yuriko Yano acknowledges USDA, National Institute of Food and Agriculture Grant, Award number 2015-67020-23454. A. Leeper, B. Lawrence, and J. LaMontagne acknowledge support from National Science Foundation Grant DEB-1745496, the University Research Council Collaborative Grant from DePaul University, and the Huron Mountain Wildlife Foundation.

1. Drought induces changes in the nitrogen (N) and phosphorus (P) cycle but most plant species have limited flexibility to take up nutrients under such variable or unbalanced N and P availability. Both the degree of flexibility in plant N:P ratio and of root symbiosis with arbuscular mycorrhizal fungi might control plant resistance to drought-induced changes in nutrient availability, but this has not been directly tested. 2. Here, we examined the role of plant N:P stoichiometric status and mycorrhizal symbiosis in the drought-resistance of dominant and subordinate species in a semi-natural grassland. 3. We reduced water availability using rainout shelters (control vs. drought) and measured how plant biomass responded for the dominant and subordinate species. We then selected a dominant (Paspalum dilatatum) and a subordinate species (Cynodon dactylon), for which we investigated the N:P stoichiometric status, mycorrhizal root colonization and water-use efficiency. 4. The biomass of all dominant plant species, but not subordinate species, decreased under drought. Drought increased soil available nitrogen, and thus increased soil N:P ratio, due to decreasing plant N uptake. The dominant P. dilatatum showed a high degree of plant N:P homeostasis and a considerable reduction in biomass under drought. At the opposite, the more flexible subordinate species C. dactylon increased its N uptake and water-use efficiency, apparently due to stronger symbiosis with mycorrhizae, and maintained its biomass. 5. Synthesis. We conclude that the maintenance of N:P homeostasis in dominant species, possibly because of a large root nutrient foraging capacity, becomes inefficient when water stress limits N mobility in the soil. By contrast, we demonstrate that higher stoichiometric N:P flexibility coupled with stronger mutualistic association with mycorrhizae allow subordinate species to better withstand drought perturbations. Using a stoichiometric approach in a field experiment, our study provides for the first time clear and novel understandings of the mechanisms involved in drought-resistance within the plant-mycorrhizae-soil system.