Purpose

Nitrogen (N) enrichment can affect the composition and stability of soil organic carbon (SOC) pools by altering vegetation and soil properties. However, the response of plant-derived carbon components in soil to different N addition levels is unclear. We investigated the changes and potential driving processes of plant-derived carbon components (especially lignins and lipids) in meadow grassland soils under long-term N addition in eastern Inner Mongolia, China.

Materials and methods

Biomarker technology was utilised to analyse changes in plant-derived carbon components (C_>20 free lipids, bound lipids, and lignin phenols) in soil under different N addition levels, including changes in soil chemical properties, enzyme activity, plant biomass, and diversity under N addition, as well as the specific pathways involved.

Results and discussion

We found that high levels of N addition significantly reduced the concentration of soil lignin phenols whereas increased the accumulation of lipids (free and bound lipids). Compared with changes in plant biomass and diversity, soil chemical properties and enzyme activity play a more significant role in regulating the accumulation and degradation of plant-derived carbon. Structural equation modelling (SEM) showed that decreases in lignin phenol concentration were related to specific biochemical decomposition processes (increased polyphenol oxidase activity and decreased C/N). The increase in lipids associated with the protective effects of minerals mediated by pH.

Conclusions

In general, plant-derived carbon components showed inconsistent responses to N addition, lignin phenol concentration decreased and lipid concentration increased, which was mainly related to the change of soil biochemical properties. Plant-derived carbon components only showed significant changes under high N addition levels. Furthermore, our research indicates that SOC sequestration and functioning are highly dependent on soil biochemical properties, which weakens the influence of changes in plant carbon input on soil carbon storage.

中文翻译：

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草甸草原土壤脂质和木质素酚对氮添加的不同响应

目的

氮（N）富集可以通过改变植被和土壤性质来影响土壤有机碳（SOC）库的组成和稳定性。然而，土壤中植物来源的碳成分对不同氮添加水平的响应尚不清楚。我们研究了长期施氮条件下内蒙古东部草甸土壤中植物源碳成分（特别是木质素和脂质）的变化和潜在驱动过程。

材料和方法

利用生物标记技术分析不同施氮水平下土壤中植物源碳成分（C _>20游离脂、结合脂和木质素酚）的变化，包括土壤化学性质、酶活性、植物生物量和多样性的变化N添加下的情况，以及所涉及的具体途径。

结果与讨论

我们发现，高水平的氮添加显着降低了土壤木质素酚的浓度，同时增加了脂质（游离和结合脂质）的积累。与植物生物量和多样性的变化相比，土壤化学性质和酶活性在调节植物源碳的积累和降解方面发挥着更显着的作用。结构方程模型 (SEM) 显示，木质素酚浓度的降低与特定的生化分解过程（多酚氧化酶活性增加和 C/N 降低）有关。脂质的增加与 pH 介导的矿物质的保护作用有关。

结论

总体而言，植物源碳组分对氮素添加的响应不一致，木质素酚浓度降低，脂质浓度升高，这主要与土壤生化性质的变化有关。植物来源的碳成分仅在高氮添加水平下才表现出显着变化。此外，我们的研究表明，SOC的封存和功能高度依赖于土壤生化性质，这削弱了植物碳输入变化对土壤碳储存的影响。