Precipitation and temperature are important drivers of soil respiration. The role of moisture and temperature are generally explored at seasonal or inter-annual timescales; however, significant variability also occurs on hourly to daily time-scales. We used small (1.54 m2), throughfall exclusion shelters to evaluate the role soil moisture and temperature as temporal controls on soil CO2 efflux from a humid tropical forest in Puerto Rico. We measured hourly soil CO2 efflux, temperature and moisture in control and exclusion plots (n = 6) for 6-months. The variance of each time series was analyzed using orthonormal wavelet transformation and Haar-wavelet coherence. We found strong negative coherence between soil moisture and soil respiration in control plots corresponding to a two-day periodicity. Across all plots, there was a significant parabolic relationship between soil moisture and soil CO2 efflux with peak soil respiration occurring at volumetric soil moisture of approximately 0.375 m3/m3. We additionally found a weak positive coherence between CO2 and temperature at longer time-scales and a significant positive relationship between soil temperature and CO2 efflux when the analysis was limited to the control plots. The coherence between CO2 and both temperature and soil moisture were reduced in exclusion plots. The reduced CO2 response to temperature in exclusion plots suggests that the positive effect of temperature on CO2 is constrained by soil moisture availability.
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机译：降水和温度是土壤呼吸的重要驱动力。湿度和温度的作用通常在季节或年际尺度上进行探讨；但是，每小时到每天的时间尺度也会发生很大的变化。我们使用小型（1.54 m 2 ）穿透降雨避难所来评估土壤湿度和温度作为暂时控制波多黎各热带热带森林中土壤CO2排放的作用。我们在六个月的控制区和排除区（n = 6）中测量了每小时的土壤CO2排放，温度和湿度。使用正交小波变换和Haar小波相干性分析了每个时间序列的方差。我们在对应于两天周期的控制区中发现了土壤水分和土壤呼吸之间的强烈负相关性。在所有样地中，土壤水分与土壤CO2排放之间存在明显的抛物线关系，在土壤水分体积约为0.375 m 3 / m 3 时出现峰值土壤呼吸。我们还发现，在较长的时间范围内，CO2与温度之间的正相干性较弱，并且当分析仅限于对照图时，土壤温度与CO2外排之间存在显着的正相关。在排除图中，CO2与温度和土壤水分之间的一致性降低了。在排他图中，CO2对温度的响应降低，这表明温度对CO2的积极影响受到土壤水分有效性的限制。
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