Temperature dependence of the contribution of soil water content to soil respiration in a monsoon influenced temperate deciduous forest

Soil respiration (Rs) in forest soils is a key flux governing forest carbon balance and the global carbon cycle. Because this flux is expected to respond rapidly to climate warming, understanding the controls on Rs is essential for predicting changes in forest carbon balance induced by warming. In natural field conditions, soil temperature (Ts) and soil water content (SWC) often covary seasonally, which tends to limit our ability to isolate and quantify the independent contribution of SWC and to evaluate how its contribution varies with temperature. Although changes in the Rs response to temperature have been reported, few studies have quantitatively identified such patterns from field observations and examined whether the relative contribution of SWC becomes more evident across temperature conditions. Here, we used two years of continuous automated chamber measurements in a temperate deciduous forest to assess how the relative contribution of SWC varies with Ts by comparing models across temperature ranges, and to evaluate whether a breakpoint occurs in the Rs response to Ts and whether that breakpoint is observed near the temperature range where the contribution of SWC increases. At the annual scale, the explanatory power of SWC alone was limited, but the relationship between SWC and Rs was significant. In contrast, above 15 °C, the relationship between SWC and Rs strengthened consistently, indicating that the relative contribution of SWC became more evident under warm soil conditions. Piecewise regression of the relationship between Rs and Ts identified a breakpoint near 17 °C, and models including this breakpoint improved fit relative to an exponential model. These results suggest a possible difference in the relative importance of controls on Rs across temperature conditions. Therefore, projections of forest Rs may benefit from considering temperature dependent changes in the contribution of SWC, particularly near the temperature range where this contribution becomes more evident.