Abstract

Natural ¹³C abundance and chemical structure of different organic matter (OM) pools of Haplic Chernozem in contrasting land use variants (steppe and long-term bare fallow) are described. The sequence of OM decomposition in soils is traced. The pattern of changes in OM chemical structure of virgin chernozems under steppe from free (LF_fr) to occluded states (LF_occ) follows the pattern characteristic of the initial stages in decomposition, namely, the degree of OM aromaticity and hydrophobicity increases as well as the degree of its microbial degradation. The products of LF_occ microbial decomposition adsorb on clay particles of the corresponding fraction. The clay-bound OM has a pronounced aliphatic nature with a considerable contribution of long-chain alkyls; it displays the highest degree of decomposition and the maximum contribution of polypeptides, which is consistent with its “heaviest” isotope signature among all studied OM pools. The chemical structure of the residue fraction is in many respects similar to that of the clay fraction and is enriched in short-chain alkyls of predominantly microbial origin. An almost complete absence of fresh organic material input to the soil of a bare fallow over a long period (52 years) causes a sharp increase in the degree of microbial decomposition of the available organic material in all studied OM pools, which is confirmed by their “heavier” isotope signature. The amount of the most easily available and energetically attractive fragments of organic material (O-Alk) for microbial community decreases, whereas the degrees of OM decomposition and hydrophobicity increase. An increase in the share of aromatic fragments and the degree of OM aromaticity suggests a selective accumulation of the most chemically stable aromatic compounds.

中文翻译：

---

不同土地利用下冰冻钙质有机质的天然 13C 丰度和化学结构

摘要

描述了在对比土地利用变体（草原和长期裸露）中 Haplic Chernozem 不同有机物质 (OM) 池的天然¹³ C 丰度和化学结构。追踪土壤中有机质分解的顺序。草原下原始黑钙土从游离态（LF _fr）到闭塞态（LF _occ）的OM化学结构变化模式遵循分解初始阶段的模式特征，即OM芳香性和疏水性程度增加以及其微生物降解的程度。LF _occ的产品微生物分解吸附在相应馏分的粘土颗粒上。粘土结合的 OM 具有明显的脂肪族性质，长链烷基的贡献相当大；它显示出最高的分解程度和多肽的最大贡献，这与其在所有研究的 OM 库中的“最重”同位素特征一致。残渣部分的化学结构在许多方面与粘土部分相似，并且富含主要来源于微生物的短链烷基。长期（52 年）内几乎完全没有新鲜有机物质输入到裸露的休耕地土壤中，导致所有研究的 OM 池中可用有机物质的微生物分解程度急剧增加，这由它们的“更重”的同位素特征。微生物群落中最容易获得且最具能量吸引力的有机物质 (O-Alk) 片段的数量减少，而 OM 分解和疏水性的程度增加。芳香族片段份额的增加和 OM 芳香性的程度表明化学性质最稳定的芳香族化合物的选择性积累。