Concentration and biodegradability of dissolved organic carbon derived from soils: A global perspective

Highlights: • Both the concentration and biodegradability of soil-derived DOC vary considerably on the global scale. • Mean annual precipitation primarily drives the variability in DOC concentration. • DOC composition mainly controls the variations in DOC biodegradability. Dissolved organic carbon (DOC), as active and mobile carbon, plays a critical role in terrestrial and aquatic ecosystems. However, it remains unclear how the concentration and biodegradability of soil-derived DOC (extracted from pore water or soil leachates) vary over a global scale and what determines the variations in DOC concentration and biodegradability. Here we addressed this issue by synthesizing the dataset involved in 121 sites from 39 literatures worldwide, and analyzed the patterns and drivers of DOC concentration and biodegradability. Our results showed that the DOC concentration in either pore water or soil leachates varied considerably, with mean values of 33.2 mg L⁻¹ in pore water and 213.5 mg kg⁻¹ in soil leachates, respectively. Mean annual precipitation (MAP) was the dominant control on the variability in soil-derived DOC concentration. Our results also revealed that the biodegradability of DOC in pore water was significantly lower than that in soil leachates, with the means of 16.5% versus 28.7%, respectively. Specific UV absorbance (SUVA₂₅₄, a parameter used for evaluating dissolved aromatic carbon content) was the primary indicator predicting the spatial variation in DOC biodegradability, whereas MAP exerted limited effects on DOC biodegradability. These results demonstrate the high biodegradability of soil-derived DOC, highlighting its crucial role in the global carbon cycle under climate change.