Negative priming effect from tree leaf and root residues with contrasting chemical composition

Changes in soil organic carbon (SOC) decomposition in response to fresh plant residue inputs (i.e., the priming effect) represent an important biogeochemical process controlling soil C dynamics. However, the variations in priming induced by the addition of leaf and root residues with different chemical compositions among tree species and their potential mechanisms are not yet well known. We conducted a 90-day incubation experiment and explored the responses of priming effect to the ¹³C-labelled leaf and root residues of Cyclobalanopsis glauca, Cunninghamia lanceolata, Acacia confusa and Manglietia fordiana and further examined the relationships between the priming and the chemical compositions of these tree residues. Our results show that tree residue inputs decreased native SOC mineralization by approximately 20–59%, and root residues induced more pronounced or comparable negative priming effects than leaf residues. Moreover, the intensities of the negative priming were greater in soils supplemented with C. glauca and C. lanceolata residues than in soils supplemented with A. confusa and M. fordiana residues. The magnitude of the negative priming effect was inversely correlated with K content in plant residues but positively correlated with lignin content, lignin/N ratio and C/N ratio. The structural equation model indicates that residue K content, lignin/N ratio, as well as plant-derived microbial biomass carbon (MBC) and dissolved organic carbon (DOC) were the key derivers of the priming, with these drivers together explaining approximately 82% of the variations in the cumulative priming effects. Overall, our study suggests that tree root residues generally induce a more negative priming than tree leaf residues, but the extent of priming varied with tree species. Chemical properties of tree residues can help to improve our understanding of the priming mechanisms that could lead to a more precise estimation of SOC dynamics.