Plant S deficiency is common, but the role of S-containing amino acids such as cysteine in plant S uptake is unknown. We applied ¹⁴C-, ³⁵S-, ¹³C-, and ¹⁵N-labelled cysteine to wheat and oilseed rape rhizospheres and traced the plants’ elemental uptake. Both plants absorbed 0.37–0.81% of intact cysteine after 6 h with no further increase after 24 h. They absorbed 1.6–11.5% ³⁵S and 12.3–7.6% ¹⁵N from cysteine after 24 h and utilised SO₄²⁻ as their main S source (75.5–86.4%). Added and naturally occurring cysteine-S contributed 5.6 and 1.1% of total S uptake by wheat and oilseed rape, respectively. Cysteine and inorganic S derived from cysteine contributed 24.5 and 13.6% of uptake for wheat and oilseed rape, respectively, after 24 h. Oilseed rape absorbed ~10-fold more S from cysteine and SO₄²⁻ than did wheat. The highest absorption of free cysteine should be in the organic-rich soil patches. Soil microorganisms rapidly decomposed cysteine (t_1/2 = 1.37 h), and roots absorbed mineralised inorganic N and S. After 15 min, 11.7–14.3% of the ³⁵S-cysteine was retained in the microbial biomass, while 30.2–36.7% of the SO₄²⁻ was released, suggesting that rapid microbial S immobilisation occurs after cysteine addition. Plants acquire N and S from cysteine via unidirectional soil-to-root nutrient flow, and cysteine is an important S source for plants.

植物缺硫很常见，但含硫氨基酸（如半胱氨酸）在植物硫吸收中的作用尚不清楚。我们将¹⁴ C-、³⁵ S-、¹³ C- 和¹⁵ N-标记的半胱氨酸应用于小麦和油菜的根际，并追踪植物的元素吸收。两种植物在 6 小时后吸收了 0.37-0.81% 的完整半胱氨酸，24 小时后不再增加。他们在 24 小时后从半胱氨酸中吸收了 1.6–11.5% ³⁵ S 和 12.3–7.6% ¹⁵ N，并利用了 SO ₄ ²⁻作为他们的主要 S 源（75.5-86.4%）。添加的和天然存在的半胱氨酸 S 分别占小麦和油菜总 S 吸收量的 5.6% 和 1.1%。24 小时后，半胱氨酸和源自半胱氨酸的无机硫对小麦和油菜的吸收量分别贡献了 24.5% 和 13.6%。油菜从半胱氨酸和 SO ₄ ^{2− 中}吸收的 S比小麦多 10 倍。游离半胱氨酸的最高吸收应在富含有机物的土壤斑块中。土壤微生物迅速分解半胱氨酸 (t _1/2 = 1.37 h)，根吸收矿化无机 N 和 S。15 分钟后，11.7-14.3% 的³⁵ S-半胱氨酸保留在微生物生物量中，而 30.2-36.7% SO ₄ ²⁻被释放，表明在添加半胱氨酸后发生快速微生物 S 固定。植物通过从土壤到根的单向营养流从半胱氨酸中获取 N 和 S，而半胱氨酸是植物的重要 S 来源。