中国东部土壤水溶性有机物荧光特征及地域分异

Spatial Variation of Fluorescence Excitation of Water Soluble Organic Matter in Eastern China

测定中国东部地区 2 0种土类 46个表土样品水溶性有机物的荧光光谱、分子量以及 p H值 ,分析了水溶性有机物荧光光谱的一般特征、荧光光谱与其平均分子量的关系以及荧光强度的地域分异特性 ,与此同时比较分析了土壤富里酸的相关特征。结果表明研究区土壤水溶性有机物和富里酸具有相似的荧光光谱特征和地域分异特性 ,即在所研究的浓度范围内两者的荧光发射光值与有机物浓度成良好的线性正相关关系 ,而荧光强度与分子量分布无直接相关性。研究区土壤水溶性有机物和富里酸荧光强度均具有自北向南递降的趋势 ;土壤 p H可能是影响水溶性有机物荧光特征及空间分异的主要因素。

Forty six top soil samples covering 20 soil types were collected from eastern China mainly in the summer of 1998 and early spring of 2000. Water soluble organic matter (WSOM) of the samples were extracted with 2∶1 weight ratio of soil to water. Fluorescence excitation spectroscopy was recorded with Hitachi F 2500 fluorescent photometer and molecular size distribution of WSOM was determined with Sephadex G 25. All WSOM samples were not processed with pH adjusting and concentrating. Correlation analysis was used to study spatial variation of the intensity of fluorescence excitation per unit carbon of WSOM and its relationship with average molecular size. Also, the same analyses were performed on fulvic acids extracted from part of the soil samples. It was found that no significant negative correlation existed between the intensity of fluorescence excitation per unit carbon of WSOM and molecular size of WSOC, but partial correlation became true with pH as the controlling factor, showing pH is important to excitation intensity of WSOM without pH adjustment. No similar relationship was found for FA samples, which was considered to be partly due to the small amount of samples of FA (only 12 samples). Both the intensity of fluorescence excitation per unit carbon of WSOM and FA showed the same trend, increasing from south to north in the study area, which was similar to the trend of pH, average molecular size of both WSOM and FA, but opposite to that of the temperature and precipitation. The pH value of soil may play an important role in regulating spatial variation of fluorescent property of WSOM, which needs further investigation.