Evaluating soil dissolved organic matter as a proxy for soil organic matter properties across diverse ecosystems

Soil organic matter (SOM) includes the soil dissolved organic matter (SDOM), an active pool in carbon biogeochemistry that contributes to vital ecosystem services such as carbon sequestration. Although SDOM properties could be related to SOM bioavailability and persistence, it needs to be confirmed that SDOM properties are related to SOM dynamics in diverse ecosystems. We collected and analyzed 31 soil samples from three ecosystems (12 croplands, 8 grasslands, and 11 forests) in western China to assess the characteristics of SOM and SDOM using multiple methods, including optical, isotopic, biomarker, and wet chemical extraction methods. Three independent multifunctionality statistical methods were used to evaluate the measured SOM or SDOM properties, and to derive a quantitative metric of the SOM persistence, defined as the organic matter persistence index (PI). The influencial SOM and SDOM properties were further confirmed by feature selection algorithms. We evaluated the relationship between the PI derived from SOM (PI_SOM) and that of the SDOM (PI_SDOM). Generally, forest soil had the highest SOM persistence, followed by grasslands and then croplands. In forests and grasslands, PI_SDOM was highly positively related to PI_SOM, indicating that it is reasonable to evaluate SOM persistence using SDOM properties as proxies in those two ecosystems. In croplands, the SOM persistence was not strongly related to the SDOM properties. We conclude that SDOM properties can be assessed rapidly and conveniently as a surrogate for SOM bioavailability and persistence, the SDOM metrics should be used cautiously because the SDOM-SOM relationship is ecosystem-dependent. Overall, this work advances the application of multi-property statistical methods for better understanding of SOM properties.