Mineral Stabilization of Soil Organic Sulfur at the Continental Scale

Abstract

Declining atmospheric sulfur (S) deposition makes S an emerging limiting macronutrient for 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, total organic S is dominated by mineral-associated organic S (MAOS; 61% ± 26%); this pool is stabilized by mineral protection but saturates at ~600 μg S/g soil. Compared with particulate organic S (POS), which is relatively labile and does not saturate, MAOS is more decomposed, chemically diverse, and climate-sensitive. Higher temperature accelerates S mineralization in both pools, but their ability to supply available S varies with moisture regime because MAOS stabilizes in wetter soils while POS remains labile. This continental-scale reassessment of the soil S cycle reveals that secondary minerals play a dual role in soil S cycling by stabilizing organic S and retaining sulfate, providing a mechanistic basis for nutrient management and carbon sequestration in response to climate change in an S-scarce future.