Soil respiration in tropical forests represents a major source of carbon dioxide (CO₂) to the atmosphere. The magnitude of this large flux is projected to change in response to climate change, with global implications due to the disproportionate role of tropical forests in the carbon cycle. Evaluating diel patterns of soil respiration concomitantly with biophysical drivers is a valuable approach for elucidating the mechanisms controlling soil respiration. We measured hourly soil respiration rates in a tropical moist forest in Puerto Rico over a 3‐year period using automated chambers, as well as soil temperature/moisture, air temperature, relative humidity, and photosynthetically active radiation. Hourly soil respiration exhibited as much as threefold variation on diel time scales (monthly diel amplitude ranged from 1 to 7 μmol CO₂ m⁻² s⁻¹), and both the magnitude and shape of diel patterns changed significantly from month to month. Soil respiration peaked in the morning and late afternoon with a midday decline that was evident during the warmest summer months. The relationship between soil respiration and soil temperature differed during daytime versus the night, with a nonlinear relationship in the daytime but a significant positive linear relationship at night. These findings suggest factors other than/in addition to temperature could be controlling soil respiration during the day; however, soil respiration did not correlate with any of the other measured biophysical variables. Overall, our results highlight the potential role of aboveground processes as drivers of soil respiration at diel time scales, especially in closed canopy tropical forests with low diel variation in soil temperature/moisture.

中文翻译：

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土壤呼吸的显着Diel变化表明波多黎各热带潮湿森林的地上和地下控制

热带森林中的土壤呼吸是二氧化碳（CO ₂）到大气中。由于热带森林在碳循环中的作用不成比例，预计这种大通量的大小将响应气候变化而变化，具有全球影响。与生物物理驱动程序一起评估土壤呼吸的迪尔模式是阐明控制土壤呼吸的机制的一种有价值的方法。我们使用自动隔室在3年内测量了波多黎各热带潮湿森林中每小时的土壤呼吸速率，以及土壤温度/湿度，空气温度，相对湿度和光合有效辐射。每小时土壤呼吸在diel时间尺度上表现出多达三倍的变化（每月diel振幅范围为1至7μmolCO ₂  m ^-2  s ^-1），并且diel模式的大小和形状在每个月中都有很大变化。在早晨和下午，土壤呼吸达到峰值，在最热的夏季月份中午出现下降。白天和晚上，土壤呼吸与土壤温度之间的关系有所不同，白天呈非线性关系，而晚上则呈显着的正线性关系。这些发现表明，除了温度以外，还可以控制白天的土壤呼吸。然而，土壤呼吸与其他任何测量的生物物理变量均不相关。总体而言，我们的结果强调了地上过程在diel时间尺度上作为土壤呼吸驱动力的潜在作用，