Long‐term fertilization affects chemical composition of dissolved organic carbon by changing soil properties

Abstract Soil dissolved organic carbon (DOC) plays a key role in fundamental biogeochemical processes; however, the influences of different types of fertilization on the chemical composition and properties of DOC molecules in soils are poorly understood. In this study, DOC samples were extracted from gray desert soils treated with five fertilization treatments: (a) chemical nitrogen, phosphorus and potassium fertilizers; (b) pig and cattle manure; (c) 50% nitrogen from manure and 50% nitrogen from chemical fertilizer; (d) total chemical fertilizers and total manure; and (e) no fertilization (control). Results showed that manure application increased the aromatic carbon by 135.7% and decreased the aliphatic carbon levels by 29.6%, implying manure application promotes the labile carbon consumption and the stable carbon enrichment. The available nutrients and available forms of magnesium were positively associated with the labile carbon groups, and the available forms of calcium were positively associated with the stable carbon groups, demonstrating that the availability of soil nutrients and minerals are influential factors on composition of carbon‐containing groups in DOC. Moreover, the fertilization method had negative direct effects and positive indirect effects on composition of carbon‐containing groups in DOC via soil physicochemical factors, and various forms of mineral ions were the strongest explanatory factors (explaining nearly 51%) of composition of carbon‐containing groups variation in DOC. These findings indicated that soil physicochemical factors play an important role as mediators in the influence of fertilization practices on the composition of carbon‐containing groups in DOC.