Diverse prokaryotic strategies associated with soil organic matter priming

Labile C inputs can alter soil organic matter (SOM) mineralisation rates through the priming effect, but the microbial communities associated with this process remain poorly understood. This study investigated two soils with contrasting nutrient supply potential, assessing the prokaryotic abundance and composition associated with priming via 16S ribosomal RNA (rRNA) gene and reverse transcript quantitative PCR (qPCR), and sequencing. The RNA:DNA ratio, used as a proxy for protein synthesis potential (PSP), was calculated to indicate microbial growth strategy. We hypothesised that differentiating microbial responses to labile C addition from r- and K-strategists could explain the contrasting priming effects observed. Both soils exhibited increased SOM mineralisation and microbial biomass under priming, though to different extents. Priming was linked to responses in few taxa, particularly from within Actinobacteria and Proteobacteria. Potential r-strategists, such as (Pseud)Arthrobacter , showed rapid growth and decreased PSP in both soils. In contrast, bacterial K-strategists exhibiting increased growth and PSP were more frequently found in one soil and may explain the increased priming observed. We also frequently observed elevated relative rRNA reverse transcript abundance in predatory bacteria, consistent with an activation response. These findings highlight the complexity of microbial responses to labile C inputs and the value of growth and PSP metrics.