The input of fresh carbon can either enhance or suppress the mineralization rate of native soil organic carbon (SOC), a process known as the priming effect. The priming effect plays a crucial role in terrestrial carbon cycling. Although previous studies have attempted to elucidate its mechanisms and responses to nitrogen (N) addition, existing findings remain inconsistent. Using soils from different forest types and soil layers with contrasting soil physico-chemical and microbial properties along an elevation gradient, this study demonstrated that priming intensity peaked in the early stage and then declined and remained stable in the late stage, and the involving mechanisms also shifted with time. Moreover, carbon-induced priming intensity was not affected by nitrogen addition. The researchers’ finding appeared August 2, 2025 in Soil Ecology Letters.

A series of studies associated in soil priming have been conducted by Feng Liu's team at the Wuhan Botanical Garden, Chinese Academy of Sciences. For example, they find deep soil in subtropical forest had higher priming intensity than surface soil, and microbial properties control soil priming and exogenous carbon incorporation.

In this study, they selected 51 soil samples from different elevations and depths across the Taibai Mountain in the Qinling Range. A 30-day laboratory incubation experiment was conducted using ¹³C-labeled glucose and N addition. During incubation, they monitored CO₂ emission rates, as well as changes in dissolved organic carbon, dissolved total nitrogen, microbial biomass carbon, microbial biomass nitrogen, extracellular enzyme activities, microbial community composition, and soil pH. By analyzing the relationship between priming intensity and the responses of these variables, they elucidated the mechanisms driving priming effects at different stages and their responses to N addition.

The results showed that priming intensity varied significantly, peaking within the first 4 days of incubation before gradually declining and stabilizing over the remaining 26 days. Following glucose addition, soil microbial biomass, SOC-derived DOC content, qCO₂, and the relative abundance of copiotrophic microbes significantly increased. These responses were strongly correlated with early-stage priming intensity. In the late stage, extracellular enzyme activity significantly increased and showed a positive correlation with priming intensity. This suggests that early-stage priming was primarily driven by increased microbial biomass and abiotic release of mineral-protected organic matter, whereas late-stage priming was driven by enhanced extracellular enzyme activity.

Although N addition suppressed microbial biomass and SOC mineralization, this inhibitory effect did not differ significantly between treatments with or without glucose addition, indicating that N addition did not alter glucose-induced priming.

This study reveals the temporal dynamics of priming intensity and the shift in underlying mechanisms over time, providing insights for a dynamic understanding of ecosystem carbon processes. Additionally, when assessing N effects, it is essential to distinguish the carbon-induced effect and N-induced effect to accurately evaluate the associated processes.
DOI：10.1007/s42832-025-0340-0