Mineral stabilization of soil organic sulfur at the continental scale

Zhuojun Zhang, M. Francesca Cotrufo, Benjamin L. Turner, Hai-Ruo Mao, Chao Liang, Mohsen Shakouri, Mengqiang Zhu

Declining atmospheric sulfur (S) deposition makes S an emerging limiting macronutrient to plants, yet the stability and dynamics of soil organic S - the largest terrestrial S pool supplying plant-available sulfate via mineralization - remain unclear. Across North American soils, mineral-associated organic S (MAOS), a stabilized pool by mineral protection, dominates (61 ± 26% of the total soil S) but saturates at ~ 600 µg S g-1 soil. Compared with labile particulate organic S (POS) that does not saturate, MAOS is more decomposed, chemically diverse, and climate sensitive. Projected global warming accelerates S mineralization in both pools, but shifting moisture regimes drive their divergence in supplying available S, with MAOS stabilizing in wetter soils while POS remains labile. This comprehensive reassessment of soil S cycle at the continental scale reveals a mineral “gatekeeper” that both shields organic S and retains sulfate, providing a mechanistic basis for nutrient management and carbon sequestration in response to climate change in a S-scarce future.