Abstract: We explored the responses of the quantity and quality of soil dissolved organic matter (DOM) to short-term nitrogen (N) addition across an addition gradient (0, 40, and 80 kg N·hm^-2·a^-1) and their correlation with bacterial communities in Pinus taiwanensis forest in the Daiyunshan Nature Reserve, Fujian, China. Soil DOM and bacterial community composition were measured using three-dimensional fluorescence and parallel factor analyses combined with high-throughput sequencing. The results showed that compared with the control, N-addition reduced the content of dissolved organic carbon (DOC) and the humification index (HIX) of DOM in the 0-10 and 10-20 cm soil layers, with significant reduction under the high N addition (80 kg N·hm^-2·a^-1). Results of parallel factor analysis further showed that the relative content of humus-like components (C1, C2) in DOM decreased following N addition. Short-term N addition reduced the relative abundance of copiotrophic bacteria (Proteobacteria and Acidimicrobiia), but increased the relative abundance of oligotrophic bacteria (Spartobacteria). The relative abundance of copiotrophic bacteria were positively correlated with the HIX and refractory humus-like components (C1, C2) and negatively correlated with the relatively easily decomposed fulvic acid-like component (C3), whereas the pattern was opposite for oligotrophic bacteria. It is indicated that bacterial communities with different life strategies had obvious preference for difficult- and easy-to-decompose components in DOM under N addition treatments. We speculated that the transformation of soil microbial life strategies under the background of increasing N deposition might alter DOM components.

Key words: simulated nitrogen deposition, forest soil, fluorescent component, microbial strategy, oligotrophic bacteria.