Decreases in priming effect vary with labile carbon type under long-termnitrogen addition in a boreal forest

The priming effect induced by labile carbon inputs can influence soil organic carbon (SOC) decomposition, whichcan be regulated by nitrogen (N) availability. However, how long-term N addition affects the priming effect isstill unclear. Here, we address this issue by combining results from an experiment and a data synthesis. For theexperiment, soils were collected from a 12-year <i>in-situ </i>N addition in a boreal forest, and 13C-labeled glucose,glycine or oxalic acid were added as a rate of 2.5% of SOC. Further, we conducted a global data synthesis with188 observations from 50 studies from forests to compare priming in response to transient incubation addition<i>versus </i>continuous field N addition. The positive priming effect caused by glycine was highest among the three Ctypes especially in the control treatment, <i>i.e.</i>, a significant interaction between N addition and C type. Thesevariations could be attributed to differences in microbial substrate metabolic pathways. N addition significantlysuppressed the priming effect, consistent with trends observed in the global data synthesis. However, the extentof N inhibition from field studies was marginally lower than that from incubation studies, suggesting that the Ninhibition on priming may be to some extent overestimated. Overall, our results emphasize that the inhibition oflong-term N addition on priming may depend on labile C type. More studies with soils from long-term N additionin the field are urgently needed for accurately assessing SOC decomposition via the priming effect in the contextof chronic N deposition in boreal forests.