川西平原还田秸秆腐解释放DOM的光谱特征

为掌握川西平原保护性耕作模式下还田秸秆腐解过程的光谱学特性，追溯还田秸秆对川西地区生态系统结构的影响过程，采集了该地区主要种植作物油菜、水稻的秸秆样本，利用紫外-可见吸收光谱(UV-Vis)、三维荧光光谱(3D-EEM)和傅里叶变换红外光谱(FTIR)三种光谱学表征手段，阐明秸秆各腐解阶段溶解性有机质(DOM)的光谱学特征，对比不同农作物秸秆快速淋溶阶段DOM(0~0.5 d)与腐解过程(0.5~90 d)的光谱学特征差异性，解析其变化机理。结果表明： 还田秸秆腐解过程中DOM的光谱学特性差异明显，伴随着芳香性物质的溶出、降解以及新生腐殖类物质的形成；由秸秆快速淋溶阶段释放DOM的E₂/E₃值最大而SUVA₂₅₄值最小可知该阶段溶出的物质芳香性和分子量相对较小；其芳香性组分的溶出主要集中在腐解前期(≤10 d)，表现于该阶段E₂/E₃值逐渐减小且SUVA₂₅₄值逐渐增大，DOM中多糖峰、芳香C和酰胺峰变弱；难分解的纤维素、半纤维素和大分子蛋白质主要在腐解后期被降解；DOM中酚类、羰基类和羧酸类物质数量增加，使得DOM与有机污染物、金属离子的相互作用增强，进而调节农田土壤中污染物的迁移转化过程。本研究为川西平原秸秆还田的环境意义提供了基础数据和新证据，为该地区农业废弃物处理与资源化提供了依据。

Study on Spectral Characteristics of Dissolved Organic Matter Collected from the Decomposing Process of Crop Straw in West Sichuan Plain

The rape and rice straws were collected in the West Sichuan Plain.The spectral characteristics of dissolved organic matter (DOM)released from the decomposing process of crop straws were characterized by the UV-Vis spectrum,Fourier trans-form infrared spectrum (FTIR)and three-dimensional excitation emission matrix fluorescence spectrum (3D-EEM).The differ-ence of spectral characteristics of DOM in rapid leaching stage (0~0.5 days)and straw decomposing process (0.5~90 days) was clarified.The effect of straws to ecosystem structure in the conservation tillage pattern was tracked,and the variation mech-anism was analyzed.The difference of DOM spectral characteristics in decomposing processes was significant.The dissolution of aromatic substances,degradation of components and formation of humus also presented in the processes.The E2/E3 value of DOM released from the rapid leaching stage of the straw was the highest,while the value of SUVA254 was the lowest,which suggested the aromaticity and molecular weight of DOM at the stage were relatively lower than those in other periods.The disso-lution of aromatic components predominantly occurred in the early stage (≤10 days)when the E2/E3 value decreased gradually, but the SUVA254 value increased.And,the peak of polysaccharide,aromatic carbon and amide absorbent apex in DOM weak-ened.However,the persistent cellulose,hemicellulose and macromolecular protein were decomposed in the later period.The IR bands of DOM consisted of the amino acids,peptides,proteins,polysaccharides,phosphate skeleton,purine bases,pyrimidine and other components were mainly caused by the vibration,stretching,bending or hydrogen bonding of N—H,O—H, C—O , C—C ,C—O,C—H and —COO- functional groups.Microorganism activities were vigorous in the early and middle stages of decomposition,which made degradable sugar and protein-like rapidly running out.DOM released from rape straws in the early stage showed a high bioavailability,due to the protein-like with the low molecular weight and unstable characteristics.The DOM of rice straws contained more organic matter than the rape,and had more humus relatively.The —OH and C—O of DOM can disturb the migration and transformation of non-ionic polar OCs through covalent bonds in the soil.With the decomposition,—OH was,to a certain extent,decomposed by microorganisms.In this case,the interaction between DOM and OCs became weaker,and the phenols,carbonyls and carboxylic acids gradually enhanced the interaction between DOM and OCs or metal i-ons.Therefore,DOM regulated the migration and transfer processes of OCs in farmland soils.This study provides the basic data and new evidence for environmental significance of straw-return in the West Sichuan Plain,and the support for agricultural waste treatment and resource recycle in the area.