What if publication bias is the rule and net carbon loss from priming the exception?

Abstract. Priming effects in soil science describe the influence of labile carbon inputs on rates of microbial soil organic matter mineralisation, which can either increase (positive priming) or decrease (negative priming). While both positive and negative priming effects occur in natural ecosystems, the latter is less documented in the peer-reviewed literature and the overall impact of priming effects on the carbon balance of vegetated ecosystems remains elusive. Here, we highlight three aspects which need to be discussed to ensure (rhizosphere) priming effects are correctly perceived in their ecological context and measured at appropriate scales: (i) We emphasize the importance of evaluating net C balances because usually experimental C inputs exceed C losses meaning even positive priming doesn’t cause net C-loss; (ii) We caution against publication bias, which forces overrepresentation of positive priming effects, neglects negative or no priming, and potentially misguides conclusions about C loss; and (iii) We highlight the need to distinguish between general priming effects and rhizosphere- specific priming, which differ in their scale and driving factors, and hence require different methodological approaches. Future research should explore potential discrepancies between laboratory and field studies and examine the role of rhizosphere priming in nutrient cycling and plant nutrition.