Jeong Soo Park, Seung Jin Joo, Jaseok Lee, Dongmin Seo, Hyun Seok Kim, Jihyeon Jeon, Chung Weon Yun, Jeong Eun Lee, Sei-Woong Choi and Jae-Young Lee. J Ecol Environ 2023;47:. https://doi.org/10.5141/jee.23.077

Although rainfall is a major determinant of soil moisture content (SMC), various factors affect SMC. The effects of these environmental factors contribute to spatial heterogeneity in SMC, which influences diverse ecological processes. To better understand the dynamics in SMC, litter and slope gradient should be considered. To this end, we analyzed the impacts of litter and slope gradient on SMC from 2020 to 2021 on Mt. Jeombong, located in a temperate deciduous broadleaf forest. We classified the study period into foliage (with a developed canopy) and non-foliage (after leaf fall) seasons. Our results indicated that SMC was affected by slope gradient and litter layer. Rainfall absorption occurred more at gentle slope, leading to higher SMC. Additionally, rainfall absorption was interpreted as being intercepted by the litter layer. Consequently, the correlation coefficient between SMC increment and rainfall was lower in the non-foliage season (R² = 0.37–0.56) than in the foliage season (R² = 0.72–0.84). With temporal progression, however, SMC response to rainfall increased where the litter was thickly accumulated, suggesting that litter interception was gradually diminished by decomposition. In this study, spatial heterogeneity in the litter layer and slope gradient substantially influenced the supply of soil moisture from rainfall.

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.

As climate change accelerates, environmental factors are expected to fluctuate as well. To gain insight into soil respiration (Rs) dynamics, it is essential to conduct long-term measurements of Rs alongside environmental variations. To this end, we examined Rs associated with environmental variables from 2018 to 2024 at a site located on Mt. Jeombong, which is situated in a temperate deciduous broadleaf forest. The interannual variation in Rs was not explained by soil temperature but was primarily associated with rainfall regimes. The mean Rs for April–November was substantially different during the study period and was strongly correlated with cumulative rainfall at all measurement points (R² = 0.68–0.94). These variations were largely attributed to changes in autotrophic respiration (Ra). Furthermore, Rs differed significantly between nearby measurement points (p < 0.05), despite their proximity within a 100 m by 100 m plot, apparently reflecting point-level differences in responses of Rs to environmental drivers that were likely modulated by uneven litter accumulation. Overall, at our site located in temperate deciduous forests, Rs primarily fluctuates as a result of rainfall variation, and Rs variations are strongly influenced by the heterogeneity in the litter deposition.

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 moisture content (SMC) often covary seasonally, which tends to limit our ability to isolate and quantify the independent contribution of SMC and to evaluate how its contribution varies with temperature. Although temperature thresholds in Rs have been reported, few studies have quantitatively identified such thresholds from field observations and interpreted potential shifts in the dominant controls based on how moisture responses differ across the threshold. Here, we used two years of continuous automated chamber measurements in a temperate deciduous forest to estimate a Ts threshold for Rs and to assess how the relative contribution of SMC varies with Ts by comparing models across temperature ranges, with particular attention to changes near the threshold. At the annual scale, the explanatory power of SMC alone was limited, but the relationship between SMC and Rs was significant. In contrast, above 15 °C, the relationship between SMC and Rs strengthened consistently, indicating that the contribution of SMC is constrained at low Ts but increases markedly at high Ts. Piecewise regression of the relationship between Rs and Ts identified a Ts threshold near 17 °C, and models including this threshold improved fit relative to an exponential model. These results show that the relative contribution of SMC can change across a specific temperature range, suggesting that changes in the relative influence of SMC on Rs variability across the threshold may reorganize the dominant controls on Rs. Therefore, projections of forest Rs should jointly consider temperature dependent changes in moisture contribution and the presence of Ts thresholds.

Climate warming is altering precipitation regimes and increasing the frequency of extreme rainfall events. Soil respiration (Rs) is sensitive to these chan