中文摘要：

秸秆是农业生产的主要副产物,也是农业面源污染的新源头。秸秆还田能有效解决其减量化和资源化利用问题,国家＂十二五＂规划已明确提出＂加大秸秆还田力度,保障农业的稳产、增产和可持续发展＂。现阶段,对于典型地区不同环境条件下还田秸秆腐殖化行为的研究不多,同时对于腐殖化组分的精细化检测和分析也有待加强。针对黄土区秸秆还田问题,以紫外光谱法和荧光光谱法为切入点,分析pH值对腐殖化产物溶解性有机质（Dissolved organic matter,DOM）性质的影响,深度揭示秸秆腐殖化过程的内在本质。结果表明：在200-700nm波长范围内,DOM的紫外吸收强度先增加后减小,主要吸收峰出现于240nm附近。相对于中性（pH 7）体系,酸性（pH 6）和碱性（pH 8和9）条件下的最大吸收波长λmax值红移。SUVA254,E3/E4和A253/A203比值的规律性变化说明反应体系腐殖化程度较低,这与秸秆腐殖化周期较短有关。黄土浸提液DOM的荧光峰主要位于λex/em=250/330和λex/em=325/450区域,分别归属为紫外区类富里酸荧光峰和可见光区类富里酸和腐殖酸类物质荧光峰。随着腐殖化体系pH值的升高,荧光峰位发生红移,表明DOM苯环结构逐渐增多,共轭度有所增加,同时在λex/em=250/450附近检测到新荧光峰。pH值对荧光强度的影响主要体现在紫外区类富里酸荧光峰,峰强先升高后下降,而对可见光区荧光峰强影响不大,这与浸提液的缓冲效应、荧光猝灭（或副反应）和DOM组分结构有关。紫外光谱和荧光光谱能够一定程度上阐释pH值对秸秆腐殖化DOM性质的影响。

英文摘要：

Crop straw is the dominant by-product from agriculture and is regarded as the new source of non-point contamination.Straw incorporation is possible to solve the issues of straw reduction and reutilization,which is clearly required in the twelfth five-year-plan for national economic and social development of the People＇s Republic of China.At present,it is of noticeable lack of the investigation on straw incorporation behavior and detail humification product analysis in the representative regions under different environmental conditions.The ultraviolet and fluorescence spectrometry were used to reveal the characteristics of dissolved organic matter（DOM）,affected by pH values,in the straw humification process in loess region.The results showed：the ultraviolet absorbance of DOM samples increased firstly and then decreased with the increasing wavelength from 200 to 700nm,and the maximum absorbance peaks appeared around the wavelength of 240 nm.The maximum absorbance peaks（λmax）were greater at pH values of 6,8and 9than that of 7,and the low degree of humification was indicated from the values of SUVA254,E3/E4 and A253/A203,caused by the short period of humification.The fluorescence peaks of extracted DOM from loess appeared around the regions ofλex/em=250/330andλex/em=325/450,referred as UV fulvic-like fluorescence,and visible fulvic-like and humic-like fluorescence,respectively.The increasing pH values resulted in the greater wavelength of absorbance peak,suggesting the increased aromaticity and conjugated degree,and the novel fluorescence peak was found inλex/em=250/450.The pH values were more effective to change the UV fulvic-like fluorescence peaks intensity（increased firstly and then decreased）than that of visible fulvic-like and humic-like fluorescence,which might be related to buffer effect,fluorescence quenching（side effects）and component structure.The ultraviolet and fluorescence spectrometry were acceptable to illustrate the characteristics variation of DOM affected by pH values in the