The diel pattern of CH₄ emissions used in field sampling strategies and time-scale extrapolation is generally regarded as peaking during daytime rather than at night. However, under specific conditions such as water limitation and high temperatures that rice widely undergo, the diel patterns of CH₄ emissions remain unclear. We identified diel patterns in CH₄ flux among rice stages that experienced different water and temperature conditions, using continuous high-frequency measurements over three consecutive years of CH₄ flux in rice paddies. The results showed that a pronounced single peak in CH₄ flux occurred during the daytime (13:30–14:30) in the early rice stage. During the reproductive stage, however, the daytime CH₄ flux decreased significantly, resulting in a distinct reverse diel pattern frequently (80–86%) observed. The daytime CH₄ emissions showed no peaks and were averaged only 41.67% of the nighttime levels under water-limited conditions with high temperatures. Missing the nighttime CH₄ flux would underestimate 28.49–32.98% of the daily CH₄ emissions during the reproductive stage if the nighttime CH₄ flux was calculated using the nighttime/daytime ratio at the vegetative stage. The discovery of a distinct nocturnal peak diel pattern of CH₄ flux, contrary to the well-known daytime peak pattern, indicates that measurements and extrapolations based only on daytime data could underestimate CH₄ emissions from rice paddies.

中文翻译：

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稻田夜间峰值甲烷通量 diel 模式


野外采样策略和时间尺度外推中使用的 CH₄ 发射的 diel 模式通常被认为在白天而不是晚上达到峰值。然而，在水稻广泛经历的限水和高温等特定条件下，CH₄ 排放的 diel 模式仍不清楚。我们通过连续三年对稻田中 CH₄ 通量的连续高频测量，确定了经历不同水和温度条件的水稻阶段中 CH₄ 通量的 diel 模式。结果表明，稻早熟期白天 （13：30–14：30） CH₄ 通量出现明显的单峰。然而，在繁殖阶段，白天的 CH₄ 通量显着降低，导致经常观察到明显的反向 diel 模式 （80-86%）。白天的 CH₄ 排放没有显示峰值，在水分受限的高温条件下，平均仅为夜间水平的 41.67%。如果使用营养阶段的夜间/白天比率计算夜间 CH₄ 通量，则缺少夜间 CH₄ 通量将低估繁殖阶段每日 CH₄ 排放量的 28.49-32.98%。与众所周知的白天峰值模式相反，CH₄ 通量在夜间峰值模式的发现表明，仅基于白天数据的测量和推断可能会低估稻田的 CH₄ 排放量。