Contrasting fine root-induced rhizosphere priming effects between coniferous and broadleaved trees

The rhizosphere priming effects (RPE) influence soil organic carbon (SOC) decomposition at the root-soil interface. However, whether different tree species affect the direction and intensity of RPE has been rarely studied. The RPE was measured from the fine roots of three coniferous and four broadleaved trees with a mean age of 20 years by utilizing the 13C natural tracing technique after 135-day in situ incubation. The released carbon dioxide (CO2) from the root-soil system was trapped using an improved CO2 trapping system. The fine root RPE of broadleaved trees is negative, ranging from − 43% to − 21%. Conversely, the fine root RPE of coniferous trees is positive, ranging from 34% to 58%. The fine root non-structural carbohydrates, including soluble sugars, sucrose, and starch, in coniferous trees were all lower than in those of broadleaved trees. The non-structural carbohydrates, such as starch and soluble sugars, are the most critical factors driving the RPE of fine roots on SOC decomposition. Therefore, the direction and degree of the RPE from fine roots of tree species can be used as a reference index for selecting tree species in afforestation, especially under the broad context of carbon neutrality.