Soil freeze-thaw induces a pulse of nitrous oxide (N₂O) emissions fueled by a concomitant increase in available organic carbon (C) and nitrogen (N) substrates. These substrates are hypothesized to originate from the disruption of aggregates and microbial biomass, but experiments designed to falsify these hypotheses have been scarce. We therefore conducted a series of column experiments using intact soil cores of silt loam and loamy sand under different freezing rates and durations, factors previously identified as controlling the magnitude of subsequent N₂O emissions. We used a slower freezing rate and shorter freeze duration (6 days) as a Control, to which we compared the same freeze duration but faster freezing rate (Fast, 6 days) and the same freezing rate but longer freeze duration (Long, 21 days). All soils were frozen to ~ -2.5 °C. Upon thaw, only the silt loam emitted N₂O; we therefore focused on silt loam C, N, and aggregate dynamics. Control and Fast soils emitted similar amounts of N₂O, even though Fast soils maintained aggregate mean weight diameter (MWD). Long soils emitted 1.8 times more N₂O than Control, even though Long and Control soils exhibited similar decreases in aggregate MWD. We suggest that because in no instance were differences in N₂O emissions between treatments proportional to differences in aggregate disruption, and some soils emitted N₂O without any detectable aggregate disruption, that aggregate disruption does not play a significant, universal role in providing substrates for N₂O emissions. In contrast, larger N₂O emissions due to longer freezing durations were associated with a delayed decrease in microbial biomass. Although we did not assess microbial communities for features other than their biomass, our observations are consistent with longer freezing durations selecting for slower growing microorganisms and freeze-thaw induced N₂O emissions being fueled by microbial osmolytes.

土壤冻融引起一氧化二氮 (N ₂ O) 排放脉冲，由可用有机碳 (C) 和氮 (N) 底物的伴随增加推动。假设这些底物源自聚集体和微生物生物量的破坏，但旨在证伪这些假设的实验很少。因此，我们在不同冻结速率和持续时间下使用粉砂壤土和壤质沙的完整土芯进行了一系列柱实验，这些因素以前被确定为控制后续 N ₂的量级O排放。我们使用较慢的冷冻速度和较短的冷冻持续时间（6 天）作为对照，我们将相同的冷冻持续时间但更快的冷冻速度（快速，6 天）和相同的冷冻速度但较长的冷冻持续时间（长，21 天）进行比较）。所有土壤都被冷冻到~-2.5°C。解冻时，只有粉砂壤土释放出 N ₂ O；因此，我们专注于粉砂壤土 C、N 和骨料动力学。对照和快速土壤排放相似量的 N ₂ O，即使快速土壤保持了团聚体平均重量直径 (MWD)。长土壤排放的 N ₂ O 是对照的1.8 倍，尽管长土壤和对照土壤的聚集体 MWD 表现出类似的下降。我们建议，因为在任何情况下 N ₂都没有差异处理之间的 O 排放与聚集体破坏的差异成正比，并且一些土壤排放 N ₂ O 而没有任何可检测的聚集体破坏，该聚集体破坏在为 N ₂ O 排放提供底物方面没有发挥重要的、普遍的作用。相比之下，由于较长的冷冻持续时间，较大的 N ₂ O 排放与微生物生物量的延迟减少有关。尽管我们没有评估微生物群落的生物量以外的特征，但我们的观察结果与选择生长较慢的微生物的较长冷冻持续时间和由微生物渗透剂推动的冻融诱导的 N ₂ O 排放一致。