Abstract
Many previous research have investigated the spatial distribution of the content of soil organic matter (SOM) and soil humic substance (HS), while few work focused on the chemical composition variation of HS across geographic distance. Paddy soils, collected from different long-term fertilization treatments across a wide geographic area in subtropical China, were used to evaluate the spatial variation of HS chemical composition. The 3-dimensional fluorescence spectroscopy combined with parallel factor analysis was used to evaluate the chemical composition of the soil extractable humic substance (EHS, including humic acid and fulvic acid). Analysis of distance-decay relationship (DDR) was introduced here to study the spatial variation of the chemical compositions of these EHSs. It was found that geographic location impose greater impact on the compositional variation of soil EHS than fertilization practice. Fertilization treatments including NPK (mineral N, P and K fertilizers) and NPKS (NPK fertilizers plus straw return) exhibited significant flattened DDR slopes as compared to CK (no fertilizers), which indicated fertilization (NPK and NPKS) decreased the variation of EHS chemical composition in paddy soils across geographic distance. A positive correlation was found between variations of soil bacterial community and EHS chemical composition, and fertilization (NPK and NPKS) enhanced their relationships. This work demonstrated that although the geographic location mainly dominated the spatial variation of the soil EHS chemical composition across geographic distance, the same long-term fertilization practice could gradually domesticate the paddy soils to display more similar EHS composition.
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