Higher priming effect induced by stem than leaf and root litter

Plant litter input can affect soil organic carbon (SOC) decomposition, that is the priming effect. Variation in experimental conditions, litter characteristics and soil properties among individual studies has led to inconsistent reports of priming effects. We aimed to synthesize global patterns and drivers of the litter‐induced priming effect.

Using meta‐analysis, we synthesized 621 observations from 118 publications and performed multiple statistical approaches, including mixed‐effects meta‐regressions and variation partitioning analysis.

We showed that plant litter input stimulated SOC decomposition by an average of 42% globally, indicating an overall positive priming effect. Compared with leaf and root litter, stem litter, which had lower nitrogen (N) content, induced a greater priming effect, particularly in N‐rich cropland soils. Microbial biomass C also increased by an average of 45% following litter addition, with a greater increase under stem litter than under other litter types, consistent with the microbial N‐mining hypothesis. Experimental conditions, including incubation duration and litter addition rate, were more important in explaining priming induced by leaf and stem litter, whereas litter characteristics and soil properties, such as C:N ratio and pH, were more important in explaining root litter‐induced priming, potentially reflecting the relatively high recalcitrance of root litter. Furthermore, the effects of soil properties on the priming effect depended on litter characteristics, with particularly strong interactions observed for root litter, highlighting that root litter‐induced priming is jointly regulated by litter quality and the soil properties.

We emphasize the importance of the specificity of litter type in regulating the priming effect. Future studies should comprehensively investigate litter characteristics and their interactions with experimental conditions and soil properties using long‐term experiments to improve global predictions of SOC decomposition via the priming effect.