Global plant sulphur (S) deficiency is increasing because of a reduction in sulphate-based fertiliser application combined with continuous S withdrawal during harvest. Here, we applied ¹³C, ¹⁵N, ¹⁴C, and ³⁵S quad labelling of the S-containing amino acids cysteine (Cys) and methionine (Met) to understand S cycling and microbial S transformations in the soil. The soil microorganisms absorbed the applied Cys and Met within minutes and released SO₄²⁻ within hours. The SO₄²⁻ was reutilised by the MB within days. The initial microbial utilisation and SO₄²⁻ release were determined by amino acid structure. Met released 2.5-fold less SO₄²⁻ than Cys. The microbial biomass retained comparatively more C and S from Met than Cys. The microorganisms decomposed Cys to pyruvate and H₂S whereas they converted Met to α-ketobutyrate and S-CH₃. The microbial stoichiometries of C, N, and S derived from Cys and Met were balanced after 4 d by Cys-derived SO₄²⁻ uptake and Met-derived CO₂ release. The microbial C:N:S ratio dynamics showed rapid C utilisation and loss, stable N levels, and S accumulation. Thus, short-term organic S utilisation by soil microorganisms is determined by amino acid structure whilst long-term organic S utilisation by soil microorganisms is determined by microbially controlled stoichiometry.

全球植物硫 (S) 缺乏症正在增加，原因是硫酸盐肥料施用量减少以及收获期间持续停硫。在这里，我们对含硫氨基酸半胱氨酸 (Cys) 和蛋氨酸 (Met)应用¹³ C、¹⁵ N、¹⁴ C 和^{35 S 四元标记来了解土壤中的 S 循环和微生物 S 转化。}土壤微生物在几分钟内吸收了所施用的 Cys 和 Met，并在几小时内释放出 SO ₄ ^2-。SO ₄ ^2-在几天内被 MB 重新利用。初始微生物利用率和 SO ₄ ²⁻释放由氨基酸结构决定。_{Met 释放的 SO 4} ²⁻比 Cys少 2.5 倍。微生物生物质从 Met 中保留的 C 和 S 比 Cys 多。微生物将Cys分解为丙酮酸和H ₂ S，而将Met转化为α-酮丁酸和S-CH ₃。来自 Cys 和 Met 的 C、N 和 S 的微生物化学计量在 4 天后通过 Cys 衍生的 SO ₄ ^2-吸收和 Met 衍生的 CO _2平衡发布。微生物 C:N:S 比率动态显示出快速的 C 利用和损失、稳定的 N 水平和 S 积累。因此，土壤微生物对有机硫的短期利用由氨基酸结构决定，而土壤微生物对有机硫的长期利用由微生物控制的化学计量决定。