为探究长期氮输入对草甸草原土壤不同组分有机碳含量及化学结构影响，以内蒙古东北草甸草原为研究对象，于2010年设置0（CK）、30（N30）、50（N50）、100（N100）、150（N150）、200（N200） kg/（hm²·a）6个不同施氮水平处理，测定土壤不同组分有机碳含量及红外光谱特征。结果表明：①相比CK，长期氮输入条件下可提高土壤总有机碳（SOC）含量（增幅0.3%~13.6%），且主要表现为颗粒有机碳（POC）含量的增加（9.22%~16.39%），但降低土壤轻组有机碳（LOC）含量。②红外光谱主成分分析（PCA）结果表明，土壤LOC主要来源于脂肪碳、芳香碳、酚醇化合物，POC主要来源于芳香碳和酚醇化合物，矿物结合有机碳（MOC）主要来源于烷基碳和多糖。③相比CK，施氮处理凋落物和LOC官能团中烷氧碳（单糖+多糖）的相对强度降低，烷基碳、芳香碳相对强度增加；土壤POC和MOC官能团中烷氧碳、烷基碳及芳香碳相对强度增加，酚醇化合物相对强度降低；且施氮处理下凋落物及其不同土壤碳组分有机碳结构稳定性（芳香碳/脂肪碳）均高于CK。④结构方程模型（SEM）结果显示，随着施氮水平增加，通过提高土壤地上生物量（AGB）可促进POC和MOC的形成，但由于氮添加导致的土壤pH降低会反过来促进MOC的分解。这些结果表明，长期氮输入SOC含量的提高主要表现为土壤POC的增加，随着施氮水平增加，植物碳的输入提高SOC含量的同时通过促进土壤中凋落物残体中木质素等芳香碳的积累来提高土壤不同组分有机碳化学结构稳定性。综上所述，研究结果强调了氮输入条件下土壤颗粒有机碳的重要性以及凋落物中木质素衍生物的积累可能是介导氮输入下土壤碳固存的关键过程。

In order to explore the effects of long-term nitrogen (N) input on the content and chemical structure of different organic carbon fractions in meadow steppe soil, the meadow steppe in northeast Inner Mongolia was taken as the research object, six N input levels were setup in 2010, i.e., 0 (CK), 30, 50, 100, 150 and 200 kg(/hm²·a), the contents and infrared spectra of different soil organic carbon fractions were determined. The results showed that:1) Compared with CK, soil total organic carbon (SOC) was increased by 0.3%-13.6% under long-term nitrogen input, mainly due to the increase of particulate organic carbon (POC, 9.22%-16.39%), but light organic carbon (LOC) was decreased. 2) The results of principal component analysis (PCA) of infrared spectra showed that LOC mainly came from aliphatic carbon, aromatic carbon and phenolic alcohol compounds, POC came from aromatic carbon and phenolic alcohol compounds, and mineral-bound organic carbon (MOC) was from alkyl carbon and polysaccharides. 3) Compared with CK, the relative strengths of alkoxy carbon (monosaccharide + polysaccharide) in litter and LOC functional groups were decreased, the relative strengths of alkyl carbon and aromatic carbon were increased, the relative strengths of alkoxy carbon, alkyl carbon and aromatic carbon in POC and MOC functional groups were increased, and the relative strength of phenolic compounds was decreased under nitrogen treatment. The structural stability of organic carbon (aromatic carbon/aliphatic carbon) in litter and its different soil carbon fractions under nitrogen treatment was higher than that of CK. 4) SEM results showed that with the increase of nitrogen application, the formation of POC and MOC was promoted by increasing soil aboveground biomass (AGB), but the decrease of soil pH caused by nitrogen addition in turn promotes the decomposition of MOC. These results showed that the increase of SOC under long-term nitrogen input was mainly from the increase of soil POC. With the increase of nitrogen application, the input of plant carbon increased SOC and improved the chemical structure stability of different soil organic carbon fractions by promoting the accumulation of aromatic carbon such as lignin in litter residues. In summary, the results emphasized the importance of soil particulate organic carbon under nitrogen input and the accumulation of lignin derivatives in litter may be the key processes to mediate soil carbon sequestration under nitrogen input.

S153.6

国家重点研发计划项目（2018YFD0800802）资助。