Hydro-physical and carbon properties of peat across peatland types and climate zones

• The relationships between BD and hydro-physical parameters were investigated across different peatland types. • Carbon density can be derived from BD for peat soils with carbon content ≥ 35 %. • Relationships between BD and carbon density differed across peatland types. • Total porosity decreased linearly with BD, while macroporosity followed a power-law with BD. • K s followed a log–log relationship with BD, but functions varied by peatland type. The hydro-physical properties of peat play a pivotal role in regulating the water, nutrient, and carbon cycles of peatland ecosystems. However, our understanding of peat hydraulic properties remains limited, especially at a global perspective. In this study, we compiled a comprehensive global database of the peat physical, hydraulic, and chemical properties, including bulk density (BD), porosity, macroporosity, saturated hydraulic conductivity ( K s ), carbon content, and carbon density, encompassing tropical peatlands, boreal and temperate fens and bogs, and permafrost regions. Our primary objective was to examine how these properties varied along a BD gradient across peatland types and climate zones. The results revealed a robust linear relationship between carbon density and BD for various peatland types with carbon content exceeding 35 % ( R 2 > 0.93, p < 0.001). The carbon density of tropical peatlands was more sensitive to changes in BD than that of boreal and temperate peatlands. Total porosity was found to decrease linearly as BD increased, while macroporosity followed a power-law relationship with BD. These trends were consistent across all peatland types, underscoring a strong and reliable association between BD and both total porosity and macroporosity. Additionally, K s exhibited a general decline with increasing BD, with the relationship characterized by log–log functions that varied among peatland types and climate zones. These findings indicated that hydraulic functions of peat (e.g., carbon density, K s ) were significantly influenced by the peat-forming vegetation such as woody plants, Sphagnum , sedges, and the prevailing climatic conditions of the peatland. This study demonstrated that the key peat hydro-physical–chemical parameters—including carbon density, porosity, macroporosity, and K s could be reliably estimated using the BD, with relatively high coefficients of determination ( R 2 > 0.4), highlighting the critical importance of determining BD as a proxy for estimating other hydro-physical properties of peat when direct measurements are unavailable and potentially serving as reliable tools for estimating the carbon stock of peatlands across peatland types and climate zones.