Purpose

The aims of this study were to investigate how short-term agricultural practices varying in vegetation cover, tillage, and organic amendments affected the chemistry of aggregate-associated C and particulate organic matter (POM) after 8-year soil restoration from parent material (PM) of a Mollisol. The research allowed indicating the effects of perennialization and organic amendments on the chemical compositions of soil organic carbon (SOC) in both aggregates and POM in short-term and thereof helped to unveil the mechanisms of C sequestration and stabilization.

Material and methods

The field surface soils (0–20 cm) under 8-year natural perennials and an arable soil with organic amendments were collected. Soil aggregate fractionation method was applied to obtain three aggregate-sized fractions: macroaggregate (> 250 μm), microaggregate (53–250 μm), and silt-clay unit (< 53 μm). The coarse POM (cPOM, > 250 μm), microaggregate (53–250 μm), and silt-clay units within macroaggregate, the fine POM (fPOM, 53–250 μm), and silt-clay units within microaggregate were further separated. In all, 10 subgroups of aggregates were obtained to determine organic carbon content and chemical structure using ¹³C-NMR spectroscopy technique. The PM for the establishment of the experiment was also used.

Results and discussion

The chemical composition of SOC differed among aggregate sizes, representing different organic compositions with different decomposition stages. Compared with PM, soil restoration under natural perennial and organic amendments increased SOC in both POM and aggregate fractions; higher proportion of POM with larger proportion of plant-derived O-alkyl C was observed in arable soil than in perennials. Meanwhile, the silt-clay units, sequestrating the most of the organic C, contained larger proportions of alkyl C, aromatic C, and carbonyl C, probably due to the microbial-derived by-products. The data partially supported our hypothesis that continuous organic amendments to PM likely promoted aggregate formation and subsequently affected the chemical composition of C therein.

Conclusions

Perennialization and organic amendments increased not only the total SOC stocks in bulk soils and aggregate fractions but also changed the SOM chemistry by varying quantity and quality of plant residues. The silt-clay units contributed largely to the stock and stability of SOC during the soil development stage from PM of a Mollisol. The main mechanisms of plant-derived C sequestrated and SOC accrued were controlled probably not only by the physiochemical protection of soil aggregates but also by the microbial C sequestration capacity in silt-clay fraction at the initial stage of soil formation.

中文翻译：

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软体动物母体早期成土过程中水稳定聚集体组分中土壤有机碳的分子特征

目的

这项研究的目的是调查在从母体土壤中恢复8年后，短期农业实践在植被覆盖，耕作和有机改良剂方面的变化如何影响团聚体相关碳和颗粒有机物（POM）的化学性质。 ）的Mollisol。研究表明，多年生和有机修正对短期内团聚体和POM中土壤有机碳（SOC）化学成分的影响，并有助于揭示碳固存和稳定的机制。

材料与方法

收集了8年自然多年生植物下的田间表层土壤（0–20厘米）和有机改良的耕作土壤。应用土壤骨料分级方法获得三种骨料级分：大骨料（> 250μm），微骨料（53-250μm）和粉土-黏土单元（<53μm）。粗骨料（cPOM，> 250μm），微骨料（53–250μm）和大型骨料中的淤泥-粘土单元，精细POM（fPOM，53-250μm）和微骨料中的淤泥-粘土单元被进一步分离。使用¹³ C-NMR光谱技术，总共获得了10个聚集体亚组，以确定有机碳含量和化学结构。还使用了用于建立实验的PM。

结果和讨论

SOC的化学组成在聚集体尺寸之间有所不同，代表具有不同分解阶段的不同有机组成。与PM相比，天然多年生和有机改良剂对土壤的恢复增加了POM和骨料中的SOC。与多年生植物相比，可耕地土壤中的POM含量较高，而植物来源的O-烷基C含量较高。同时，隔离大多数有机碳的淤泥-粘土单元包含较大比例的烷基碳，芳族碳和羰基碳，这可能是由于微生物衍生的副产物所致。数据部分支持了我们的假设，即对PM进行连续的有机修正可能会促进聚集体的形成，进而影响其中C的化学组成。

结论

多年生植物和有机改良剂不仅增加了散装土壤和集料部分的总SOC存量，而且还通过改变植物残渣的数量和质量改变了SOM化学。在土壤发育阶段，粉质粘土产生的粉尘-粘土单元极大地促进了土壤有机碳的储量和稳定性。植物源碳固存和有机碳累积的主要机制可能不仅受到土壤团聚体的物理化学保护，而且还受到土壤形成初期粉质粘土部分微生物固碳能力的控制。