典型黑土区不同生态系统下土壤团聚体中胡敏酸的结构特征

STRUCTURE OF HUMIC ACID IN SOIL AGGREGATES UNDER DIFFERENT ECOSYSTEMS IN TYPICAL BLACK SOIL REGION OF NORTHEAST CHINA

为了揭示生态系统类型对土壤团聚体中腐殖质分子结构的影响,本研究以黑土区24 a长期定位试验处理下的自然草地(GL)、耕地(CL)和裸地(BL)土壤为研究对象,采用湿筛法将土壤团聚体分为>2 mm、2～0.25 mm、0.25～0.053 mm和<0.053 mm 4个粒级,运用元素分析、红外光谱和差热分析技术,对团聚体中胡敏酸(HA)的结构性质进行了研究。结果表明,生态系统类型对团聚体中HA的分子结构产生了影响。耕地各级团聚体中HA的O+S含量以及(O+S)/C比值(摩尔比)普遍高于草地相应粒级团聚体,反映了耕地土壤团聚体中HA的氧化程度高于草地;差热分析中,耕地和裸地土壤团聚体中HA的中温放热量低于草地相应粒级团聚体,且二者的热量高/中比值均高于草地,说明耕地和裸地土壤团聚体中HA的芳香性/脂族性高于草地;草地和耕地土壤团聚体中HA在2 920和2 850 cm-1处代表脂族聚亚甲基和末端甲基中C-H伸缩振动的吸收峰明显强于裸地,脂族碳/羧基碳(2 920/1 720)以及脂族碳/芳香碳(2 920/1 620)比值高于后者。与自然草地相比,耕地和裸地生态系统会增强土壤团聚体中HA的缩合度、氧化度和芳香性,提高其分子结构的稳定性。

To explore effects of ecosystems on molecular structure of humus （HS） in soil aggregates, soil samples were collected from plots of grass land（GL）, cultivated land（CL） , and bare land（BL） in a long-term （24 years） field experiment in the black soil region of Northeast China for fractionation of soil aggregates into four particle-size fractions （ 〉2 mm, 2～0.25 mm, 0.25 ～0.053 mm and 〈0.053 mm） with the wet sieving method and further for analysis of structural properties of humic acid （HA） in aggregates with element analysis, infrared spectroscopy （FTIR） and differential thermal analysis （DTA） methods. Results show that the type of an ecosystem has some effects on molecular structure of the HA in soil aggregates. The HA in soil aggregates from CL was higher that from GL in O ＋ S content and （O ＋ S）/ C ratio, which indicates that the HA in soil aggregates from CL is higher than that from GL in oxidation degree. The DTA analysis reveals that the HA in soil aggregates from CL and BL was lower than that from GL in thermal discharge under moderate temperature, but higher in high to moderate heat ratio, suggesting that the former is higher than the latter in aro- maticity/aliphaticity ratio. The HA in soil aggregates from GL and CL displays higher peaks than that from BL did at 2 920 and 2 850 cm-1, representing C-H stretching vibration of asymmetric and symmetric aliphatic （CH3 and CH2 ） , and the former was also higher than the latter in aliphatic-C/carboxylic-C （2 920/1720） and aliphatic-C/aromatic-C （2 920/ 1 620） ratios. Compared with GL, the ecosystems of CL and BL both increased condensation, oxidation and aromaticity of HA in soil aggregates, thus enhancing stability of the molecular structure of HA in soil aggregates.