Permafrost existence is closely associated with soil organic matter preservation: Evidence from relationships among environmental factors and soil carbon in a permafrost boundary area

•Soil organic carbon distribution was examined in a permafrost boundary area.•Permafrost conditions affected contributions of soil variables to organic carbon.•Permafrost existence favors soil organic matter preservation. Permafrost regions store a large amount of soil organic carbon (SOC). Although permafrost degradation with climate warming can stimulate soil organic matter (SOM) decomposition, it remains unknown that whether the permafrost existence benefits SOM preservation. Here, a boundary area of permafrost and non-permafrost zone was selected to test the hypothesis that SOM underlain by permafrost has been better preserved than the area without permafrost under similar climatic conditions. The interactions among topography, vegetation cover, permafrost, soil variables and SOC distribution were examined. The results showed the sites beneath wet meadow land covers, which are usually underlain by permafrost, have higher SOC stocks than those of alpine meadows without permafrost. Based on mixed effects models, both soil water content and bulk density explained higher SOC content variances in the sites without permafrost than the sites underlain by permafrost. The north-facing non-permafrost sites have significantly higher SOC contents than those in south-facing non-permafrost sites. Vegetation cover, aspect, and permafrost have mixing effects on SOC contents both in permafrost and non-permafrost sites. Soil particle size and the rock fragment content are good predictors for prediction of SOC contents, while the best predictor was depending on the presence of permafrost. These results suggested that under similar climatic conditions, permafrost existence favors the preservation of SOM, this should be taken into consideration in the future carbon emission from permafrost regions since permafrost degradation can lag behind climate warming in many areas.