Background

Sulfur-containing amino acids, methionine (Met) and cysteine (Cys), are important components of soil-soluble organic S and N. The effects of elemental availability and microbial density (soil or soil solution) on amino acid decomposition remain unclear.

Methods

We traced the decomposition and utilization of Met and Cys by microorganisms in soil and soil solutions using ¹⁴C, ¹⁵N, and ³⁵S labelling. Further, how microbial keep its stoichiometric homeostasis after uptake Cys and Met under various element availability was also explored.

Results

Low concentrations of Met and Cys (50 µM) can be decomposed by microorganisms in both soil and soil solutions rapidly. In soil, Met and Cys undergo three steps: uptake into microorganisms (38.4% for Cys; 56.9% for Met at 2 min), the release of CO₂, NH₄⁺, and SO₄²⁻, and the re-utilization of inorganic ions. In the soil solution, the Met and Cys were also decomposed rapidly, while the produced inorganic ions were not utilized by microorganisms, which may be due to the limited amounts of microorganisms. The Cys and Met uptake process instantly occurred and was driven by microbial carbon demand in both soil and soil solution. The microbial N and S demand regulated the re-utilization process of released inorganic ions. Soil microbes balance their S, N, and C after uptake of Met and Cys, however, this balance was disturbed by high S addition, unlike additional C or N, which may be due to the lower demand of S.

Conclusions

Low-demand elements might regulate soil microbial stoichiometry balance, and a specific fertilization strategy that balanced the high- and low-demand elements can enhance nutrients use efficiency.

中文翻译：

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元素有效性对土壤及土壤溶液中微生物分解利用含硫氨基酸的影响

 背景

含硫氨基酸、蛋氨酸（Met）和半胱氨酸（Cys）是土壤可溶性有机硫和氮的重要组成部分。元素有效性和微生物密度（土壤或土壤溶液）对氨基酸分解的影响尚不清楚。

 方法

我们使用¹⁴ C、 ¹⁵ N 和³⁵ S 标记追踪了土壤和土壤溶液中微生物对 Met 和 Cys 的分解和利用。此外，还探讨了微生物在各种元素可用性下摄取Cys和Met后如何保持其化学计量稳态。

 结果

低浓度的 Met 和 Cys (50 µM) 可以被土壤和土壤溶液中的微生物快速分解。在土壤中，Met 和 Cys 经历三个步骤：被微生物吸收（Cys 为 38.4%；Met 在 2 分钟时为 56.9%），释放 CO ₂ 、NH ₄ ⁺和 SO ₄ ²⁻ ，以及再利用无机离子。在土壤溶液中，Met和Cys也迅速分解，而产生的无机离子没有被微生物利用，这可能是由于微生物数量有限所致。 Cys 和 Met 的吸收过程立即发生，并由土壤和土壤溶液中微生物碳需求驱动。微生物对氮和硫的需求调节了释放的无机离子的再利用过程。土壤微生物在吸收 Met 和 Cys 后平衡其 S、N 和 C，然而，与额外的 C 或 N 不同，这种平衡受到高 S 添加的干扰，这可能是由于对 S 的需求较低。

 结论

低需求元素可能调节土壤微生物化学计量平衡，平衡高需求元素和低需求元素的特定施肥策略可以提高养分利用效率。