## 5 Conclusions  
This study investigated the spatial distribution and influencing factors of Se in soils of a Se-rich karst region in Zheng'an County, Guizhou Province. By comparing soils derived from two parent materials (limestone and sandstone) under different land-use types (paddy fields and drylands), we found that Se content is significantly enriched across the region, with all samples exceeding the national and global background values. Notably, Se was more concentrated in the eastern part of Banzhu Township and central Xiaoya Township.  
Parent material and land use jointly influenced Se distribution, with limestone-derived soils generally exhibiting higher Se levels. SOM emerged as the most consistent predictor of total Se content across different settings, likely due to its role in Se adsorption and redox stabilization. Although pH was not directly correlated with Se content, it may exert an indirect influence through its interaction with parent material and SOM.  
At the macro scale, topographic factors such as elevation and slope showed significant correlations with Se content in specific subregions. Elevation influenced Se indirectly by affecting SOM accumulation through climatic and biological processes, while slope affected Se distribution by altering erosion and leaching dynamics.  
These findings highlight the complex interplay between geological and ecological factors in shaping Se dynamics in karst landscapes. The results provide a scientific basis for improving land management and soil nutrient conservation in Se-rich regions. However, this study is limited by its focus on total Se rather than bioavailable forms. Future research should incorporate Se speciation, plant uptake, and seasonal dynamics to better understand Se cycling and its implications for food security and human health.  
J.B.: Supervision, Writing--Review and Editing, Conceptualization, and Investigation. C.X.: Methodology, Writing--Original Draft, Validation, Formal analysis, Investigation, and Visualization. X.X.: Investigation, Writing--Review and Editing, Funding acquisition, and Project administration. Z.H.: Software and Data Curation. J.Z.: Software, Resources, Visualization, and Data Curation. C.Y.: Investigation, Writing--Review and Editing, Y.H.: Software, Resources, Visualization, and Data Curation. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Natural Science Foundation of Guizhou Province (ZK-2022-227), the Geological Mineral Exploration and Development Fund of Guizhou Province (QDKKH2021-15), the National Natural Science Foundation of China (41907177), and the Open Research Program of the Groundwater Remediation Technology Transformation Pilot Base of Hubei Province (GRTT202003).  
Not applicable.  
The datasets used and analyzed during the current study are available from the corresponding author upon reasonable request. Requests should be directed to [PERSON] ([EMAIL_ADDRESS]).  
The authors express their gratitude to the 106 Geological Brigade of the Guizhou Provincial Bureau of Geology and Minerals for their support in gathering geological and geochemical data, as well as aiding in field surveys and sample collection.  
The authors affirm that there are no financial or personal conflicts of interest that could have influenced the results presented in this paper.