Direct addition and legacy effects of sulphur fertilisation on microbial soil organic matter mineralisation and priming effect

A promising strategy to optimise nitrogen (N) management in agriculture involves accounting for microbial soil organic matter (SOM) mineralisation and incorporating the associated N-flux into fertiliser management. While SOM mineralisation is known to be influenced by C:N stoichiometry, the role of other nutrients, particularly sulphur (S) in regulating the process remains poorly understood. This study investigated SOM priming under four S fertilisation scenarios: no S; Direct S, S legacy, and S legacy + Direct S. Glucose- 13 C was added to soils with all S fertilisation scenarios, and 13 CO 2 and CO 2 measured over a 16-day incubation period. Microbial biomass (C, N, S, P) and enzyme activities were measured, while molecular sequencing and RNA:DNA ratios assessed microbial metabolic potential and life strategies linked to priming. Glucose addition stimulated positive priming via increased enzyme activity and was associated with higher microbial biomass N and P, but not C, indicating stoichiometric regulation. This was accompanied by increased metabolic potential of both r and K-strategist SOM decomposers: Nakamurella , Microlunatus , and Cellvibrio. S legacy increased positive priming by 86% relative to NoS, whereas direct S addition to this soil reduced priming by 31%, along with reductions in enzyme activities. Legacy, but not direct S drove differences in microbial community, indicating the S-legacy-induced change in priming was associated with prevalence of a distinct microbial community with enhanced SOM turnover capacity. Upon direct S addition, this community shifted to use of the added S, reducing reliance on SOM mineralisation. The increased metabolic potential of both r-strategist ( Ohtaekwangia ) and K-strategist ( Kribella and Cellvibrio ) SOM decomposers under S legacy indicate diverse microbial life strategies were associated with priming under S fertilisation. Our findings indicate tailored S management can influence microbial processes regulating SOM mineralisation, with implications for timing and availability of N, P, and S to support more sustainable agricultural production.