• Energy Research

ABSTRACTThe joint effects of simultaneous warming and precipitation shifts on soil organic carbon (SOC)—the largest terrestrial carbon pool—remain poorly understood across large spatial extents. By evaluating a global dataset of SOC measurements in the top meter of soil through a space‐for‐change substitution approach, we show that, averaging across the globe, increased precipitation compensates for warming‐induced SOC reductions regardless of soil depth and vice versa. Although additive effects between these two factors are predominant, negative interactive effects, which exacerbate SOC losses, are also common, particularly in tropical and subtropical grasslands/savannas and Mediterranean/montane shrublands. SOC responses vary widely across the globe, primarily correlated to baseline SOC content and local climatic conditions. Notably, SOC responses in tundra systems are opposite the responses in other ecosystems, showing positive and negative responses to warming and precipitation increases, respectively. Under a scenario of 2°C air warming with projected precipitation changes, global SOC stocks in the 0–1 m depth are projected to decrease by 13.1% ± 6.6% (mean ± 95% confidence interval, or 351 ± 100 Pg C). These results demonstrate that accurately predicting SOC dynamics under climate change necessitates explicit consideration of local climatic conditions and existing SOC content in relation to concurrent precipitation shifts and warming.

ABSTRACTThe joint effects of simultaneous warming and precipitation shifts on soil organic carbon (SOC)—the largest terrestrial carbon pool—remain poorly understood across large spatial extents. By evaluating a global dataset of SOC measurements in the top meter of soil through a space‐for‐change substitution approach, we show that, averaging across the globe, increased precipitation compensates for warming‐induced SOC reductions regardless of soil depth and vice versa. Although additive effects between these two factors are predominant, negative interactive effects, which exacerbate SOC losses, are also common, particularly in tropical and subtropical grasslands/savannas and Mediterranean/montane shrublands. SOC responses vary widely across the globe, primarily correlated to baseline SOC content and local climatic conditions. Notably, SOC responses in tundra systems are opposite the responses in other ecosystems, showing positive and negative responses to warming and precipitation increases, respectively. Under a scenario of 2°C air warming with projected precipitation changes, global SOC stocks in the 0–1 m depth are projected to decrease by 13.1% ± 6.6% (mean ± 95% confidence interval, or 351 ± 100 Pg C). These results demonstrate that accurately predicting SOC dynamics under climate change necessitates explicit consideration of local climatic conditions and existing SOC content in relation to concurrent precipitation shifts and warming.

AbstractSoil biogeochemical processes may present depth‐dependent responses to climate change, due to vertical environmental gradients (e.g., thermal and moisture regimes, and the quantity and quality of soil organic matter) along soil profile. However, it is a grand challenge to distinguish such depth dependence under field conditions. Here we present an innovative, cost‐effective and simple approach of field incubation of intact soil cores to explore such depth dependence. The approach adopts field incubation of two sets of intact soil cores: one incubated right‐side up (i.e., non‐inverted), and another upside down (i.e., inverted). This inversion keeps soil intact but changes the depth of the soil layer of same depth origin. Combining reciprocal translocation experiments to generate natural climate shift, we applied this incubation approach along a 2200 m elevational mountainous transect in southeast Tibetan Plateau. We measured soil respiration (Rs) from non‐inverted and inverted cores of 1 m deep, respectively, which were exchanged among and incubated at different elevations. The results indicated that Rs responds significantly (p < .05) to translocation‐induced climate shifts, but this response is depth‐independent. As the incubation proceeds, Rs from both non‐inverted and inverted cores become more sensitive to climate shifts, indicating higher vulnerability of persistent soil organic matter (SOM) to climate change than labile components, if labile substrates are assumed to be depleted with the proceeding of incubation. These results show in situ evidence that whole‐profile SOM mineralization is sensitive to climate change regardless of the depth location. Together with measurements of vertical physiochemical conditions, the inversion experiment can serve as an experimental platform to elucidate the depth dependence of the response of soil biogeochemical processes to climate change.

AbstractSoil biogeochemical processes may present depth‐dependent responses to climate change, due to vertical environmental gradients (e.g., thermal and moisture regimes, and the quantity and quality of soil organic matter) along soil profile. However, it is a grand challenge to distinguish such depth dependence under field conditions. Here we present an innovative, cost‐effective and simple approach of field incubation of intact soil cores to explore such depth dependence. The approach adopts field incubation of two sets of intact soil cores: one incubated right‐side up (i.e., non‐inverted), and another upside down (i.e., inverted). This inversion keeps soil intact but changes the depth of the soil layer of same depth origin. Combining reciprocal translocation experiments to generate natural climate shift, we applied this incubation approach along a 2200 m elevational mountainous transect in southeast Tibetan Plateau. We measured soil respiration (Rs) from non‐inverted and inverted cores of 1 m deep, respectively, which were exchanged among and incubated at different elevations. The results indicated that Rs responds significantly (p < .05) to translocation‐induced climate shifts, but this response is depth‐independent. As the incubation proceeds, Rs from both non‐inverted and inverted cores become more sensitive to climate shifts, indicating higher vulnerability of persistent soil organic matter (SOM) to climate change than labile components, if labile substrates are assumed to be depleted with the proceeding of incubation. These results show in situ evidence that whole‐profile SOM mineralization is sensitive to climate change regardless of the depth location. Together with measurements of vertical physiochemical conditions, the inversion experiment can serve as an experimental platform to elucidate the depth dependence of the response of soil biogeochemical processes to climate change.

AbstractSoil organic carbon (SOC) changes under future climate warming are difficult to quantify in situ. Here we apply an innovative approach combining space-for-time substitution with meta-analysis to SOC measurements in 113,013 soil profiles across the globe to estimate the effect of future climate warming on steady-state SOC stocks. We find that SOC stock will reduce by 6.0 ± 1.6% (mean±95% confidence interval), 4.8 ± 2.3% and 1.3 ± 4.0% at 0–0.3, 0.3–1 and 1–2 m soil depths, respectively, under 1 °C air warming, with additional 4.2%, 2.2% and 1.4% losses per every additional 1 °C warming, respectively. The largest proportional SOC losses occur in boreal forests. Existing SOC level is the predominant determinant of the spatial variability of SOC changes with higher percentage losses in SOC-rich soils. Our work demonstrates that warming induces more proportional SOC losses in topsoil than in subsoil, particularly from high-latitudinal SOC-rich systems.

AbstractSoil organic carbon (SOC) changes under future climate warming are difficult to quantify in situ. Here we apply an innovative approach combining space-for-time substitution with meta-analysis to SOC measurements in 113,013 soil profiles across the globe to estimate the effect of future climate warming on steady-state SOC stocks. We find that SOC stock will reduce by 6.0 ± 1.6% (mean±95% confidence interval), 4.8 ± 2.3% and 1.3 ± 4.0% at 0–0.3, 0.3–1 and 1–2 m soil depths, respectively, under 1 °C air warming, with additional 4.2%, 2.2% and 1.4% losses per every additional 1 °C warming, respectively. The largest proportional SOC losses occur in boreal forests. Existing SOC level is the predominant determinant of the spatial variability of SOC changes with higher percentage losses in SOC-rich soils. Our work demonstrates that warming induces more proportional SOC losses in topsoil than in subsoil, particularly from high-latitudinal SOC-rich systems.