Sorption affects amino acid pathways in soil: Implications from position-specific labeling of alanine
Sorption affects amino acid pathways in soil: Implications from position-specific labeling of alanine
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DOI：
10.1016/j.soilbio.2014.01.015
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发表时间：
2014-05
影响因子：
9.7
通讯作者：
M. Dippold;M. Biryukov;Y. Kuzyakov
中科院分区：
文献类型：
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作者：
M. Dippold;M. Biryukov;Y. Kuzyakov
有机-矿物相互作用是土壤中碳长期稳定的最重要机制。然而，部分吸附的低分子量有机物质(LMWOS)仍然是生物可利用的。用14C或13C对物质进行均匀标记只反映了一个LMWOS分子中C原子的平均命运。位置特异性标记的亚分子工具可以分析单个官能团的代谢途径，从而更深入地了解吸附和微生物利用的机理。14C标记的丙氨酸分别被五种吸附剂吸附：两种不同晶体结构的铁氧化物：针铁矿和赤铁矿；两种2：1层的粘土矿物-蒙脱石和1：1层-高岭石；以及活性碳。在随后将这些吸附剂添加到壤质单层Luvisol中后，我们分析了14C在土壤溶液中的释放、微生物的利用以及从丙氨酸的各个C位流出的14CO2。所有的吸附剂都将丙氨酸作为一个完整的分子结合(第一、第二或第三位的吸附相同)。吸附丙氨酸的生物利用度及其微生物转化途径强烈依赖于吸附剂。针铁矿和活性炭吸附丙氨酸的量最高(∼占输入总量的45%)，而吸附的丙氨酸C的微生物利用率最低(分别为26%和22%)。解吸的丙氨酸在前5小时内达到矿化高峰，结合粘土矿物的丙氨酸矿化最为明显。结合丙氨酸对CO2的初始矿化作用总是在C-1位(-COOH基团)最高。C-2和C-3的矿化速率在10-50h后超过了C-1的氧化，反映了经典的生化途径：1)脱氨，2)糖酵解中C-1的脱羧基，3)柠檬酸循环中C-2和C-3的氧化。糖酵解(C-1氧化)和柠檬酸循环(C-2和C-3氧化)这两条代谢途径之间的比例取决于吸附丙氨酸的微生物可利用性。高效性导致糖酵解C-1氧化达到峰值，随后通过柠檬酸循环突然转变为氧化。吸附的丙氨酸的微生物利用率低，进而导致所有三个位置不那么明显的平行氧化，并导致丙氨酸C在微生物化合物中的相对掺入较高。对碳通量的模拟表明，吸附的丙氨酸在78h后被结合到微生物生物量中，并进一步稳定在吸附剂表面。位置特异性标记能够从单个分子位置确定碳利用的途径和速率，以及它对不同吸附机制的依赖。我们的结论是，位置特异性标记是一种独特的工具，可以详细了解土壤中碳稳定的亚分子转化过程、机制和速率。
Organo-mineral interactions are the most important mechanisms of long-term C stabilization in soils. Nevertheless, a part of the sorbed low molecular weight organic substances (LMWOS) remains bioavailable. Uniformly labeling of substances by14C or13C reflects only the average fate of C atoms of a LMWOS molecule. The submolecular tool of position-specific labeling allows to analyze metabolic pathways of individual functional groups and thus reveals deeper insight into mechanisms of sorption and microbial utilization.Alanine labeled with14C in the 1st, 2nd or 3rd position was adsorbed to five sorbents: two iron oxides with different crystalline structure: goethite and haematite; two clay minerals with 2:1 layers – smectite, and 1:1 layers – kaolinite; and activated charcoal. After subsequent addition of these sorbents to a loamy haplic Luvisol, we analyzed14C release into the soil solution, its microbial utilization and14CO2efflux from individual C positions of alanine.All sorbents bound alanine as an intact molecule (identical sorption of 1st, 2nd or 3rd positions). The bioavailability of sorbed alanine and its microbial transformation pathways depended strongly on the sorbent. Goethite and activated charcoal sorbed the highest amount of alanine (∼45% of the input), and the lowest portion of the sorbed alanine C was microbially utilized (26 and 22%, respectively). Mineralization of the desorbed alanine peaked within the first 5 h and was most pronounced for alanine bound to clay minerals. The initial mineralization to CO2of bound alanine was always highest for the C-1 position (–COOH group). Mineralization rates of C-2 and C-3 exceeded the C-1 oxidation after 10–50 h, reflecting the classical biochemical pathways: 1) deamination, 2) decarboxylation of C-1 within glycolysis, and further 3) oxidation of C-2 and C-3 in the citric acid cycle. The ratio between two metabolic pathways – glycolysis (C-1 oxidation) versus citric-acid cycle (oxidation of C-2 and C-3) – was dependent on the microbial availability of sorbed alanine. High availability causes a peak in glycolysis C-1 oxidation followed by an abrupt shift to oxidation via the citric acid cycle. Low microbial availability of sorbed alanine, in turn, leads to a less pronounced, parallel oxidation of all three positions and to a higher relative incorporation of alanine C into microbial compounds. Modeling of C fluxes revealed that a significant portion of the sorbed alanine was incorporated in microbial biomass after 78 h and was further stabilized at the sorbents' surfaces.Position-specific labeling enabled determination of pathways and rates of C utilization from individual molecule positions and its dependence on various sorption mechanisms. We conclude that position-specific labeling is a unique tool for detailed insights into the submolecular transformation processes, mechanisms and rates of C stabilization in soil.