Abstract Food waste digestate (FWD) composting is hindered by severe nitrogen loss, primarily through ammonia (NH 3 ) and nitrous oxide (N 2 O) emissions. While biochar amendment is known to mitigate this loss, the optimal pyrolysis temperature to maximize conservation remains unclear. This study decouples the distinct influence of pyrolysis temperature (300, 400, and 800 °C) of hardwood biochar on nitrogen conservation by linking biochar properties to microbial community dynamics. A critical trade-off is revealed: 300 °C biochar maximized NH 3 reduction (39.2% vs. control, n = 2, p < 0.05) but was coincided with the enrichment of nirK/S -harboring denitrifiers (e.g., Luteimonas ), posing a potential challenge from increased N 2 O emissions. Conversely, 800 °C biochar achieved the greatest N 2 O reduction (47.5% vs. control, n = 2, p < 0.05), an outcome consistent with suppressed microbial denitrification. Critically, biochar produced at 400 °C achieved an optimal balance, likely through enhanced NH 3 adsorption and the fostering of a microbial community correlated with lower N 2 O emissions, which ultimately led to a 46.3% reduction in total nitrogen loss (vs. control, n = 2, p < 0.05), the highest performance among all treatments. This work guides the selection of biochar pyrolysis temperature toward targeted nitrogen conservation and sustainable FWD valorization. Graphical Abstract
Li et al. (Wed,) studied this question.