In soils, cysteine and methionine represent the predominant constituents of the low molecular weight organic S, but their role in plant nutrition and soil S cycling is unclear. Cysteine and methionine uptake by pot-cultivated wheat and oilseed rape and their cycling were evaluated using ¹⁴C and ³⁵S labelling. About 0.16%–0.30% of ¹⁴C from cysteine and methionine was absorbed by the plants after 6 h, indicating that the plants could utilise organic S, with oilseed rape showing higher ability than wheat to take up intact organic S and its derivative inorganic S. Plants utilised organic S with much lower efficiency than inorganic S because most organic S was decomposed by microorganisms. Nitrogen (N) addition enhanced plant S uptake, as high N uptake stimulates S immobilization. About 28%–33% and 67–71% of ¹⁴C from cysteine and methionine, respectively, were retained in the microbial biomass (MB), a much higher proportion of ¹⁴C from cysteine was released as ¹⁴CO₂ from the soil than from methionine. Further, 16%–25% and 61%–72% of ³⁵S from cysteine and methionine, respectively, were retained in the MB, and 35%–42% and 5%–9% were released from it as SO₄²⁻. Microbial carbon (C) and S use efficiency for cysteine was lower than for methionine, whereas plants utilised higher amounts of cysteine-derived S as sulphate. The higher microbial utilisation rate of methionine by soil microorganisms, compared with cysteine, may reduce the bioavailability of this compound in the soil solution, and, consequently, its uptake by plants.

在土壤中，半胱氨酸和蛋氨酸是低分子量有机S的主要成分，但它们在植物营养和土壤S循环中的作用尚不清楚。使用¹⁴ C和³⁵ S标记评估了盆栽小麦和油菜油菜吸收的半胱氨酸和甲硫氨酸及其循环。^14的约0.16％–0.30％半胱氨酸和蛋氨酸中的碳在6小时后被植物吸收，表明植物可以利用有机S，油菜比小麦吸收完整的有机S及其衍生的无机S的能力更高。植物使用的有机S含量低得多效率比无机S高，因为大多数有机S被微生物分解。氮（N）的添加会增加植物对S的吸收，因为高N的吸收会刺激S的固定。来自半胱氨酸和蛋氨酸的¹⁴ C中分别保留了微生物生物量（MB）中的¹⁴ C的28％–33％和67–71％，与土壤中的¹⁴ CO ₂相比，从半胱氨酸中释放的¹⁴ C _2的比例要高得多来自蛋氨酸。此外，在^35中，有16％–25％和61％–72％半胱氨酸和蛋氨酸中的S分别保留在MB中，并以SO ₄ ^2-的形式释放35％–42％和5％–9％。半胱氨酸的微生物碳和碳利用效率低于蛋氨酸，而植物利用的半胱氨酸来源的硫作为硫酸盐的利用率更高。与半胱氨酸相比，土壤微生物对蛋氨酸的微生物利用率较高，可能会降低该化合物在土壤溶液中的生物利用度，从而降低其对植物的吸收。