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

Tana E Wood,Matteo Detto,Whendee L Silver,Han Yh Chen

doi:10.1371/journal.pone.0080965

Abstract

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.

Highlights

In an era of significant and rapid environmental change, understanding biophysical controls on soil respiration is of immense importance
In this study we investigated hourly to daily changes in soil CO2 efflux in a relatively a-seasonal humid tropical forest in Puerto Rico to determine (1) the timescale over which CO2 efflux varies, (2) the relationship of this variation to soil temperature and moisture, and (3) how these relationships are affected by experimental reduction in soil moisture
Soil respiration in control plots showed high coherence with soil moisture for a broad range of time scales, with a peak correlation corresponding to a two-day periodicity (Fig. 1)

Summary

Introduction

In an era of significant and rapid environmental change, understanding biophysical controls on soil respiration is of immense importance. While considerable research has addressed seasonal and inter-annual patterns in soil respiration in tropical forests [5,7,10,13], less is known about the role of temperature and precipitation on shorter time-scales (e.g., hours to days) [8,12]. Laboratory incubations of tropical forest soils support this theory, showing increased soil respiration rates with increasing temperature when carbon (C) and nutrients are not limiting [17,18,19]. It follows that soil respiration under field conditions will respond to short-term variation in soil temperature (i.e., hours to days)

Methods

Results

Discussion

Conclusion