Urbanization altered regional soil organic matter quantity and quality: Insight from excitation emission matrix (EEM) and parallel factor analysis (PARAFAC).

Soil organic matter (SOM) play an important role in soil ecology and global carbon dynamic. As one of the most sever and irreversible land use change, urbanization could alter the regional carbon storage and composition pattern. However how urbanization influence on SOM is still unclear. In this study, we collected soil samples from highly urbanized area of Beijing, China and explore the quantity and quality variations of SOM by using fluorescence spectroscopy in combine with parallel factor analysis (PARAFAC). The results shown that the soil physic-chemical properties were shaped by urbanization. Comparing to nature soil, moisture content, total organic carbon and total nitrogen in urban and rural soil significantly decreased. The fluorescence spectrum demonstrated that SOM quality was also altered by urbanization induced environmental changes. Five fluorescent compounds in SOM was identified by PARAFAC model and three of them was assigned to humic-like substances. The fluorescence intensity of humic-like substances in nature land was significantly higher than of rural and urban land, meanwhile microbial related substance accumulated in urban land in comparison with rural and nature land. The multivariate analyses further reveal the relationship between soil physic-chemical properties and SOM composition. These results suggest that urbanization could not only decrease the SOM quantity but also change the SOM composition. The SOM loss caused by urbanization was mainly consist of humic-like substance loss. Besides urbanization also stimulate the accumulation of microbial related substance in SOM which highlight the importance of microorganism is SOM dynamic.