Galactosamine can be used as an indicator for microbial extracellular polymeric substances (EPS), an important source of stable organic matter in agricultural soils

四个实验形成了一个连续的计划，以阐明EPS(胞外聚合物)在农业土壤环境中的作用，基于以下两个中心假设：(1)EPS是微生物坏死体的重要组成部分，可以用阳离子交换树脂(CER)从土壤中提取。(2)氨基半乳糖(GalN)指示土壤中微生物的EPS。在第一个实验中，将通过培养土壤细菌和土壤真菌来研究微生物EPS的形成，在没有或存在无SOM无菌沙的情况下，使用甘油和淀粉作为碳源。在第二个实验中，将测试简单(甘油或玉米源淀粉)和复合(玉米源纤维素或玉米秸秆)13C标记底物在四种土壤中形成细菌和真菌EPS的能力，由于土壤pH和施肥历史的不同，它们的真菌/细菌比例不同。在第三个实验中，将监测葡萄糖和纤维素的分解，以研究两种土壤的碳利用效率(CUE)和热力学效率，由于施肥历史的不同以及EPS的存在或不同，两种土壤的真菌与细菌比例不同。在第四个实验中，通过在一种土壤上施加一种简单易得的底物(玉米源淀粉)来促进细菌EPS的形成，以及一种更顽固的底物(玉米源纤维素)来促进真菌EPS的形成，将诱导土壤中微生物EPS的形成。新形成的EPS的持久性和集料稳定效果将被监测70天。底物的C/N比一般将调整为40，在实验1中使用(NH4)2SO4，在实验2、3和4中使用(15NH4)2SO4。在所有实验中，将结合化合物特有的δ13C和δ13N分析来分析CER提取的EPS的氨基糖浓度。此外，还将检查每股收益提取物中的总有机碳、总δ15N、总碳水化合物、总蛋白质和总脱氧核糖核酸。土壤中有机碳、微生物量13C、总15N、微生物量15N、酶活性(N-乙酰--D-氨基葡萄糖苷酶和酪氨酸肽酶)和氨基糖将结合其化合物特有的δ13C和δ13N分析。在土壤大气中，将测量总CO2和13CO2的演变。在实验3中，将使用微量热计对热量产生进行额外监测。

Four experiments form a consecutive programme for elucidating the role of EPS (extracellular polymeric substances) in agricultural soil environments, based on the following two central hypotheses: (1) EPS are an important component of microbial necromass, which can be extracted from soil with cation exchange resins (CER). (2) Galactosamine (GalN) indicates microbial EPS in soil. In the first experiment, microbial EPS formation will be investigated by cultivating soil bacteria and soil fungi, using glycerol and starch as a C source in the absence or presence of SOM-free sterile sand. In the second experiment, simple (glycerol or maize-derived starch) and complex (maize-derived cellulose or maize straw) 13C labelled substrates will be tested for their ability to form bacterial and fungal EPS in four soils, differing in their fungi to bacteria ratio due to differences in soil pH and fertilization history. In the third experiment, glucose and cellulose decomposition will be monitored to investigate carbon use efficiency (CUE) and thermodynamic efficiency in two soils, differing in their fungi to bacteria ratio due to differences in fertilization history and due to the absence or presence of EPS. In the fourth experiment, microbial EPS formation in soil will be induced by applying to one soil a simple and easily available substrate (maize-derived starch) that promotes bacterial EPS formation and a more recalcitrant substrate (maize-derived cellulose) that promotes fungal EPS formation. The persistence and aggregate stabilizing effect of the freshly formed EPS will be monitored for 70 days. The C/N ratio of the substrates will be generally adjusted to 40, using (NH4)2SO4 in experiment 1 and (15NH4)2SO4 in experiments 2, 3, and 4. In all experiments, CER extracted EPS will be analysed for their concentration of amino sugars, combined with their compound-specific δ13C and δ13N analysis. EPS extracts will be additionally checked for total organic 13C, total δ15N, total carbohydrates, total protein, and total deoxy-ribonucleic acid (DNA). In the soil, soil organic 13C, microbial biomass 13C, total 15N, microbial biomass 15N, enzyme activity (N-acetyl--D-glucosaminidase and tyrosine-peptidase) and amino sugars will be measured, combined with their compound-specific δ13C and δ13N analysis. In the soil atmosphere, the evolution of total CO2 and 13CO2 will be measured. In experiment 3, heat productions will be additionally monitored using microcalorimetry.