The response of microbial necromass C and its contribution to SOC to vinasse biochar based on a pot experiment.

Introduction: Microbial necromass carbon (MNC) is a cornerstone of stable soil organic carbon (SOC), yet how biochar amendments impact its dynamics over time remains poorly understood. Methods: Here, we investigated the temporal response of MNC in a sorghum-cultivated soil amended with vinasse biochar produced at four pyrolysis temperatures (350-650 °C) over a 120-day experiment using amino sugar biomarkers and microbial profiling. Results: We reveal a distinct time-dependent biphasic response. Initially (days 30 and 60), biochar application suppressed both fungal and bacterial MNC, attributed to a nutrient-driven "priming effect" and increased microbial turnover, which accelerated decomposition. Notably, higher pyrolysis temperatures attenuated this initial loss. However, a critical reversal occurred by day 120, where all biochar treatments consistently increased MNC stocks, independent of pyrolysis temperature. This shift likely reflects the attenuation of priming and the onset of stabilization processes like aggregate formation. Discussion: Consequently, the initial negative contribution of necromass to total SOC diminished over time. These findings highlight that short-term assessments may misjudge biochar's potential for stabilizing microbial carbon. Optimizing vinasse biochar strategies requires balancing temporary priming risks against eventual long-term MNC accumulation.