Whole soil warming promotes surface soil carbon loss but deep soil carbon gain, depending on land management practices in temperate climate

The impact of management practices on the response of biogeochemical cycles to soil warming remains poorly understood. This study aimed to investigate (1) the effects of warming on soil organic carbon (SOC) and nitrogen (N) storage across soil profiles in cropland and grassland and (2) the microbial metabolism involved in these processes. To achieve these objectives, we conducted an in-situ soil warming experiment (+4°C) down to 1.0-m depth in an agricultural Cambisol in Lusignan, France. We analyzed soil microbial community composition using ester-linked fatty acid methyl ester (EL-FAME) profiling and measured extracellular enzyme activities related to SOC and nutrient cycling under both land management practices. Our results indicated that three years of soil warming had no effect on SOC and N stocks in grassland soils across the profile. In contrast, cropland surface soils (0-15 cm) showed an 18.1% and 15.0% decrease in SOC and N stocks, respectively, while deeper layers (70–90 cm) exhibited an 86.7% and 68.8% increase. These shifts in SOC and N stocks corresponded with changes in extracellular enzyme activities (C- and N-acquisition), eco-enzymatic stoichiometry, and bacterial community composition. Additionally, warming led to a slight decrease in aboveground biomass production in cropland. Furthermore, microbial biomass and community composition in surface soil exhibited management-specific responses to warming. Overall, our findings suggest that the effect of warming on SOC and N stocks depends on both soil depth and land management. Consequently, agricultural management practices could regulate SOC responses to warming by altering carbon inputs into the soil system, with implications for microbial community composition and activity. Schematic illustration of whole-soil profile warming (+4°C) responses of SOC dynamics under contrasting agricultural land management. In this illustration, the sizes of the elements denote the increase or decrease of key parameters under both land management practices in response to warming. • Warming effects on SOC and N stocks were depth-dependent in cropland but no effects were observed in grassland. • Warming effects on CN-acquisition enzymes were depth-dependent and mediated by land management. • Warming altered microbial biomass and composition in cropland but not in grassland.