Long-term moderate warming shifts soil carbon cycling but maintains carbon sinks in a subtropical forest

The lack of long-term experimental evidence on how multi-phase plant-soil interactions shape soil organic carbon (SOC) responses to warming—especially in (sub)tropical forests—hinders accurate predictions of carbon-climate feedbacks and the development of forest-based mitigation strategies. Here, we report findings from a 9-year passive ecosystem warming experiment (+0°C, +1.0°C, and +2.1°C) in a subtropical forest. We found that SOC exhibited a two-phase response distinct from previous soil-only warming experiments: initial loss (years 1–4) due to reduced topsoil mineral-associated organic carbon, followed by accumulation (years 6–9) attributed to sustained plant carbon inputs and microbial thermal adjustments that increased particulate organic carbon. Our findings indicate that some subtropical forests could continue to accumulate SOC under future moderate warming, albeit with distinct accumulation patterns of different SOC fractions across soil layers. Changes in plant-soil interactions mediating SOC fate under warming should receive increased conceptual and modeling attention moving forward.