Abstract: Soil dissolved organic matter (DOM), as a key component of the active organic carbon pool in wetland, is deeply involved in organic carbon migration, microbial transformation, and carbon release, and plays an important role in wetland carbon turnover and carbon pool stability. However, the spatial distribution and dominant controlling factors of wetland soil DOM at large geographic scales remain poorly understood. In this study, we selected 57 freshwater wetland sites spanning approximately 4000 km from north to south in eastern China. Using spectroscopic methods, we investigated the spatial distribution of soil DOM in eastern freshwater wetlands, and identified the key driving factors by integrating climatic, vegetation, soil physicochemical, and microbial community variables. The results showed that, along the north-to-south climatic gradient, the quantity and humification degree of wetland soil DOM showed a significant decreasing trend, whereas biogenic characteristics increased signifi-cantly. In terms of component composition, humic-like components dominated in colder regions, whereas protein-like components accounted for a higher proportion in warmer regions. Across different wetland types, peatlands had significantly higher soil DOM quantity than other wetland types, with a relatively high proportion of humic-like components. In contrast, lakeshore and riparian wetlands showed stronger biogenic characteristics and higher proportions of protein-like components, indicating that the specific hydrothermal environments and carbon input-output pathways of different wetland types may jointly regulate DOM accumulation and component differentiation. Results of hierarchical partitioning analysis further showed that DOM quantity, characterized by dissolved organic carbon, was mainly influenced by soil resource conditions, such as total carbon, total nitrogen, and available nitrogen, with a relative contribution of 61.5%. DOM humification degree and biogenic characteristics were mainly driven by bacterial communities and climate, with relative contributions of 34.4% and 35.7%, respectively. Spatial variation in DOM component composition was mainly regulated by climate, with a relative contribution of 64.0%. Overall, the spatial pattern of soil DOM in freshwater wetlands of eastern China is jointly shaped by the synergistic effects of climate and wetland type, while DOM accumulation, optical characteristics, and component composition are driven by different environmental constraints and ecological processes. This study could provide basic data and theoretical reference for evaluating the stability of active carbon pools in wetlands under climate change.

Key words: dissolved organic matter, climatic gradient, wetland type, spatial heterogeneity, climate change