文獻信息：
Hu Yuntao, Zheng Qing, Noll Lisa, Zhang Shasha, Wanek Wolfgang*. Direct measurement of the in situ decomposition of microbial-derived soil organic matter. Soil Biology and Biochemistry, 2020, 141: 107660. DOI: 10.1016/j.soilbio.2019.107660
摘 要：土壤有機質（SOM）是陸地生態系統中有機碳氮的主要儲存庫，而微生物殘體是其主要輸入。然而，對微生物來源的SOM的穩定機制和分解的直接測定目前仍缺乏相關知識。本文報導了一種新的15N同位素庫稀釋法，使用標記的氨基糖和胞壁肽作為示蹤劑來量化蛋白質和微生物細胞壁的分解，從而可以估算微生物來源的SOM的原位分解速率。研究結果表明，
微生物細胞壁和土壤蛋白質一樣頑固，在不同的生態系統中表現出相似的周轉時間。土壤中細菌肽聚糖主要分解為胞壁肽，微生物可直接利用這些胞壁肽而不需進一步解聚成游離胺基酸。此外，
細菌肽聚糖分解與土壤微生物量有關，而真菌幾丁質和土壤蛋白質分解與高土壤pH值、細質地有關。因此，該方法為微生物源性SOM組分的分解途徑和穩定機制提供了新的見解。
Fig. 1. Scheme of the source of the organic nitrogen polymers in soils and their decomposition products. The grey arrows indicate the depolymerization reaction of the organic nitrogen compounds.
Fig. 2. Boxplots of in situ decomposition rates of HMW organic N fractions across nine sites differing in soil types (Regosols, Gypsisols, Calcisols) and land uses (Forest, Grassland, Cropland). The central mark indicates the median of the in situ decomposition rates (μg N g−1d.w. d−1) of Gram-positive peptidoglycan, Gram-negative peptidoglycan, chitin, and proteins (n = 3).
Fig. 3. Turnover times of HMW organic N fractions across three soil types (Regosols, Gypsisols, Calcisols). Bars show the turnover times (years) of proteins, chitin, and peptidoglycan across the three soil types (n = 9, mean+1SE). Land uses are not differentiated here.
Fig. 4. Schematic representation of HMW organic N decomposition and transformation pathways in soils. Blue arrows indicate extracellular enzymatic decomposition processes, red arrows microbial uptake of bio-assimilable molecules, and the purple arrow microbial biomass turnover and necromass formation. The pools of diverse organic N compounds are shown in orange boxes. The percentages represent the range of relative contributions of specific fluxes to total organic N fluxes in the studied soils. Peptidoglycan is depolymerized to muropeptides that can be directly utilized by soil microbes instead of being further decomposed to LMW amino compounds and to monomers (<300 Da).
Fig. 5. Relative contributions of decomposition fluxes of HMW organic N fractions in soils across three soil types and land uses. Stacked bar plots show the relative abundance (RA) of the decomposition of Gram-positive peptidoglycan, Gram-negative peptidoglycan, chitin, and proteins to total organic N fluxes in soils (n = 3).
Fig. 6. Canonical correspondence analysis of high molecular weight organic N decomposition processes and soil parameters. Arrows indicate soil properties, including Gram-positive bacterial PLFA, Gram-negative bacterial PLFA, fungal PLFA, soil pH, exchangeable calcium, sand content, and clay content. Response variables (process rates) are shown in black asterisks.