Composition and contribution of Stipa bungeana root exudates to soil organic carbon fractions in the Loess Plateau

Root exudates play an important role in carbon sequestration in grassland, but the contribution of root exudates to soil organic carbon (SOC) fractions remains unclear. In this study, Stipa bungeana was analyzed, determined the composition and content of root exudates by GC–MS in a soil culture experiment and labeled with 13CO2 in a rhizibox experiment. Esters accounted for 65.38 % of root exudates, among which 1-propen-1, 2, 3-tricarboxylic acid-tributyl ester, and acetyl-tributyl citrate were the main components. During a 65-day chase period, the contents of SOC and its fractions in the rhizosphere were higher than those in bulk soil. After first day of labeling, the SOC concentration decreased by 16.95 % in the rhizosphere and reached the minimum level. Except for 13C-HC in bulk soil, which was detected three days after labeling, the rest were detected 2 h after labeling. In the rhizosphere soil, the amount of 13C in MBC and HC peaked after one day of labeling. At 65 days after labeling, the 13C-DOC, 13C-HC, and 13C-MBC in the rhizosphere significantly decreased by 59.79 %, 75.99 %, and 55.56 %, respectively. Root exudates had a rapid effect on active organic carbon fractions (MBC and DOC), and also affect the humus carbon (HC) in the short term. This study reveals the mechanism of root exudates on SOC pool during plant growth.