Sensitivity of Soil Respiration to Variability in Soil Moisture and Temperature in a Humid Tropical Forest

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 m 2 ), throughfall exclusion shelters to evaluate the role soil moisture and temperature as temporal controls on soil CO 2 efflux from a humid tropical forest in Puerto Rico. We measured hourly soil CO 2 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 CO 2 efflux with peak soil respiration occurring at volumetric soil moisture of approximately 0.375 m 3 /m 3 . We additionally found a weak positive coherence between CO 2 and temperature at longer time-scales and a significant positive relationship between soil temperature and CO 2 efflux when the analysis was limited to the control plots. The coherence between CO 2 and both temperature and soil moisture were reduced in exclusion plots. The reduced CO 2 response to temperature in exclusion plots suggests that the positive effect of temperature on CO 2 is constrained by soil moisture availability.