Amino sugars and d-amino acid enantiomers are major components of bacterial and fungal cell walls (i.e. peptidoglycan and chitin) and are often used as biomarkers of microbial residue turnover in soils. However, little is known about the in situ decomposition rates of microbial cell wall residues and how soil physicochemical properties affect this process. In this study, we investigated the in situ gross production and consumption rates of free amino sugars (glucosamine and muramic acid) and amino acids (meso-diaminopimelic acid, l-alanine, and d-alanine) by a novel isotope pool dilution assay using ¹⁵N-labeled amino compounds. Soils were obtained from six sites differing in land management (cropland, pasture, and forest) and bedrock (silicate and limestone) and incubated at three temperatures (5, 15, and 25 °C). Free glucosamine released during the decomposition of peptidoglycan and chitin contributed significantly to the extractable soil organic nitrogen pool. Gross production and consumption rates of glucosamine were higher than those of individual amino acids, i.e. L- and d-alanine. Muramic acid had a longer mean residence time (68 h compared to 2.7 h for glucosamine, L- and d-alanine) and made a negligible contribution to soil organic nitrogen fluxes, indicating that free muramic acid was not a major decomposition product of peptidoglycan in soils. Meso-diaminopimelic acid and d-alanine exhibited comparable gross production and consumption rates with l-alanine. These amino acids can be used as indicators to estimate the decomposition of peptidoglycan from bacterial cell wall residues. We found that chitin decomposition was greater in silicate soils, while peptidoglycan decomposition dominated in limestone soils. Glucosamine production rates were not correlated with soil total amino sugars, microbial community structure, or hydrolytic enzyme activities, but were highest in soils with low pH and high sand content, indicating that soil texture and soil pH may strongly influence the decomposition of amino sugar polymers. In contrast, mDAP, L- and d-alanine gross production and consumption rates were positively correlated with soil pH and clay content, due to greater depolymerization of peptidoglycan stem peptides in limestone soils. This isotope pool dilution approach strongly improves our understanding of the mechanisms and environmental controls on microbial cell wall decomposition in soils.

氨基糖和d-氨基酸对映异构体是细菌和真菌细胞壁（即肽聚糖和几丁质）的主要成分，通常用作土壤中微生物残留物周转的生物标志物。然而，人们对微生物细胞壁残留物的原位分解速率以及土壤理化性质如何影响这一过程知之甚少。在这项研究中，我们通过一种新的同位素池稀释测定法研究了游离氨基糖（氨基葡萄糖和胞壁酸）和氨基酸（内消旋二氨基庚二酸、 l-丙氨酸和d-丙氨酸）的原位总产量和消耗率。¹⁵N-标记的氨基化合物。从土地管理（农田、牧场和森林）和基岩（硅酸盐和石灰石）不同的六个地点获得土壤，并在三个温度（5、15 和 25°C）下培养。肽聚糖和几丁质分解过程中释放的游离氨基葡萄糖对可提取土壤有机氮库有显着贡献。氨基葡萄糖的总产量和消耗率高于单个氨基酸，即L-和d-丙氨酸。胞壁酸的平均停留时间更长（68 小时，而氨基葡萄糖、L- 和d为 2.7 小时）-丙氨酸），对土壤有机氮通量的贡献可以忽略不计，表明游离胞壁酸不是土壤中肽聚糖的主要分解产物。内消旋二氨基庚二酸和d-丙氨酸表现出与l相当的总产量和消费率-丙氨酸。这些氨基酸可用作评估细菌细胞壁残基中肽聚糖分解的指标。我们发现硅酸盐土壤中的几丁质分解更大，而石灰石土壤中的肽聚糖分解占主导地位。氨基葡萄糖的产生率与土壤总氨基糖、微生物群落结构或水解酶活性无关，但在低 pH 值和高含沙量的土壤中最高，表明土壤质地和土壤 pH 值可能强烈影响氨基糖聚合物的分解. 相比之下，mDAP、L- 和d-丙氨酸总产量和消耗率与土壤 pH 值和粘土含量呈正相关，这是由于石灰石土壤中肽聚糖茎肽的解聚程度更高。这种同位素池稀释方法极大地提高了我们对土壤中微生物细胞壁分解的机制和环境控制的理解。