Search Results (10)

The weathering of carbonate rocks consumes significant amounts of soil CO₂, contributing to both direct source reduction and to the enhancement of carbon sinks. This process holds substantial potential as a carbon sink, making it a critical strategy for achieving carbon neutrality and mitigating climate change. However, the control mechanisms for the reverse assessment of karst carbon sinks, with soil CO₂ as the core at the input end of karstification, are unclear. By comparing soil respiration and its δ¹³C values between karst and non-karst regions, we analyzed the impact of karstification on soil respiration. In this study, we examined the karst grassland (KG), woodland (KW), and non-karst woodland (NKW) in the karst region with identical climate conditions as the research subject, analyzing the differences in soil respiration rate (RS), flux (SRF), and isotope δ¹³C under different land-use types, and comparing them with the non-karst region to reveal the carbon sink potential of karstification in reducing carbon emissions. The results showed that after the land-use change from KG to KW in the karst region, the annual mean values of the RS and SRF increased by 55.50% and 20.94%, respectively. Additionally, the annual mean values of the soil respiration contribution to carbonate weathering in KG were approximately 8.2% higher than those in KW. In contrast, the annual mean values of RS and SRF in KW were 25.14% and 41.80% lower than those in NKW, respectively. Furthermore, the soil respiration participation in carbonate weathering in KW was about 8.9% of that in NKW. Land use change can significantly influence karst carbon sinks, with the KG exhibiting the highest carbon sink capacity. Karst soils play a crucial role in reducing atmospheric CO₂ levels and facilitating regional carbon neutralization. Therefore, the karst systems play a pivotal role in mitigating the “land use change term” (source term, E_LUC) in the global carbon balance. Full article

Rainfall significantly affects soil respiration rates by altering microbial activity and organic matter decomposition. In karst regions, it also impacts carbonate dissolution and precipitation, further influencing soil CO₂ flux. Investigating the mechanism of rainfall’s impact on soil respiration is essential for accurately evaluating and predicting changes in terrestrial ecosystems. However, our understanding of the interaction between rainfall and soil respiration in the extensive karst ecosystems of southwestern China remains limited. This study conducted field-based simulated rainfall experiments to examine variations in soil respiration rates and elucidate the associated control mechanisms through stable carbon isotope composition analysis. Simulated rainfall significantly increased the CO₂ release via soil respiration. We observed significant differences in the δ¹³C value of soil-respired CO₂ before and after simulated rainfall. Following the rain, the δ¹³C of soil-respired CO₂ was enriched compared to that before the rain. Through isotope data analysis, we found that the increased soil CO₂ emissions were primarily driven by heterotrophic respiration, likely stimulated via changes in soil moisture, affecting microbial growth conditions. Furthermore, the variation in soil moisture affected carbonate dissolution and precipitation, potentially increasing the soil CO₂ release after rainfall. In conclusion, these findings expand our understanding of rainfall’s effects on soil respiration in the native karst forests of southwestern China, contributing to the prediction of carbon cycling processes in such ecosystems. The data from this study have significant implications for addressing the release of greenhouse gases in efforts to combat climate change. Full article

The dynamic fluctuations in the soil organic carbon (SOC) stock, a fundamental part of the terrestrial ecosystem’s carbon stock, are critical to preserving the global carbon balance. Oases in arid areas serve as critical interfaces between oasis ecosystems and deserts, with land use changes within these oases being key factors affecting soil organic carbon turnover. However, the response of the soil SOC-CO₂-SIC (soil inorganic carbon) micro-carbon cycle to oasis processes and their underlying mechanisms remains unclear. Five land-use types in the Alar reclamation area—cotton field (CF), orchard (OR), forest land (FL), waste land (WL), and sandy land (SL)—were chosen as this study’s research subjects. Using stable carbon isotope technology, the transformation process of SOC in the varieties of land-use types from 0 to 100 cm was quantitatively analyzed. The results showed the following: (1) The SOC of diverse land-use types decreased with the increase in soil depth. There were also significant differences in SIC-δ¹³C values among the different land-use types. The PC(%) (0.73 g kg⁻¹) of waste land was greatly higher than that of other land-use types (p < 0.05) (factor analysis of variance). (2) The CO₂ fixation in cotton fields, orchards, forest lands, and waste land primarily originates from soil respiration, whereas, in sandy lands, it predominantly derives from atmospheric sources. (3) The redundancy analysis (RDA) results display that the primary influencing factors in the transfer of SOC to SIC are soil water content, pH, and microbial biomass carbon. Our research demonstrates that changes in land use patterns, as influenced by oasis processes, exert a significant impact on the conversion from SOC to SIC. This finding holds substantial significance for ecological land use management practices and carbon sequestration predictions in arid regions, particularly in the context of climate change. Full article

A better understanding of the factors that reduce bundle-sheath cell leakage to CO₂ (Փ), enhance 13C carbon isotope discrimination, and enhance the photosynthetic capacity of barley leaves will be useful to develop a nutrient- and water-saving strategy for dry-land farming systems. Therefore, barley plants were exposed to a novel nitrification inhibitor (NI) (3,4-dimethyl-1H-pyrazol-1-yl succinic acid) (DMPSA) and a urease inhibitor (UI) (N-butyl thiophosphorictriamide (NBPT)) with mulched drip fertigation treatments, which included HF (high-drip fertigation (370 mm) under a ridge furrow system), MF (75% of HF, moderate-drip fertigation under a ridge furrow system), LF (50% of HF, low-drip fertigation under a ridge furrow system), and TP (traditional planting with no inhibitors or drip fertigation strategies). The results indicated that the nitrification inhibitor combined with mulched drip fertigation significantly reduced bundle-sheath cell leakage to CO₂ (Փ) as a result of increased soil water content; this was demonstrated by the light and CO₂ response curves of the photosynthesis capacity (An), the apparent quantum efficiency (α), and the ¹³C-photosynthate distribution. In the inhibitor-based strategy, the use of the urease and nitrification inhibitors reduced Փ by 35% and 39% compared with TP. In the NI-HF strategy, it was found that barley could retain the maximum photosynthesis capacity by increasing the leaf area index (LAI), An, rubisco content, soluble protein, dry matter per plant, and productivity. The CO₂ and light response curves were considerably improved in the NI-HF and NI-MF treatments due to a higher 13C carbon isotope (Δ‰), respiration rate (Rd), and Ci/Ca, therefore obtaining the minimum Փ value. With both inhibitors, there was a significant difference between HF and LF drip fertigation. The NI-MF treatment significantly increased the grain yield, total chlorophyll content, WUE, and NUE by 52%, 47%, 57%, and 45%, respectively. Collectively, the results suggest that the new nitrification inhibitor (DMPSA) with HF or MF mulched drip fertigation could be promoted in semi-arid regions in order to mitigate bundle-sheath cell leakage to CO₂ (Փ), without negatively affecting barley production and leading to the nutrient and water use efficiency of barley. Full article

The presence of litter and winter snow cover can affect the decomposition of organic matter in forest soils and changes in δ¹³C values of soil-respired carbon dioxide (CO₂). However, limited information is available on the responses of CO₂ emissions from forest soils and their δ¹³C values to snow cover and litter addition over the year. We experimentally manipulated snow cover to study the impacts of light and heavy artificial snow cover on soil heterotrophic respiration and its δ¹³C values, using undisturbed large soil columns collected from two typical temperate forests in Northeastern China. Based on the average temperatures of surface forest soils in four seasons of the year in this study region, the simulations of autumn freeze–thaw, winter freeze, spring freeze–thaw, and the growing season were sequentially carried out under laboratory conditions. A set of novel analysis systems, including automated chamber equipment and laser spectroscopy analysis with high-frequency measurements for CO₂ concentrations and the ¹³C/¹²C isotopic ratios in CO₂, was used to study the effects of artificial snow cover and the presence of litter on soil heterotrophic respiration and its δ¹³C values. During the autumn freeze–thaw simulation, there were larger CO₂ emissions and less negative δ¹³C values of soil-respired CO₂ upon heavy snow cover than upon light snow cover, indicating that the presence of increased snow cover prior to winter freeze can increase the decomposition of organic C in subsurface soils under temperate forests. The δ¹³C values of soil-respired CO₂ in all treatments were, on average, less negative as the simulated spring freeze–thaw proceeded, which was contrary to the variations of the δ¹³C during the autumn freeze–thaw simulation. Soil heterotrophic respiration and its δ¹³C values during the spring freeze–thaw simulation were, on average smaller upon heavy snow cover than upon light snow cover, which differed from those during the autumn freeze–thaw and growing season simulations, respectively. Taken together, the results highlight that the effects of snow cover on soil heterotrophic respiration and its δ¹³C values under temperate forests may vary with different seasons of the year and the presence of litter. Full article

The oasis carbon pool in arid zones is an important part of the global carbon pool. There is a soil organic carbon (SOC)–soil–CO₂–soil inorganic carbon (SIC) balanced system in the soil, which facilitates the change from soil organic carbon to soil inorganic carbon. A small change in the soil carbon pool can affect the overall global carbon balance, thus affecting the conversion of soil carbon in terrestrial ecosystems. In this study, the change from soil organic carbon to soil inorganic carbon (SIC) was obtained by measuring the δ¹³C values of SIC and CO₂ in combination with stable carbon isotope techniques in cotton fields with different continuous cropping years, in the Alar Reclamation Area. Additionally, this was combined with redundancy analysis to reveal the effects of different physicochemical factors on the change amount. The results showed that the soil inorganic carbon content along the soil profile showed an increasing trend, while the soil organic carbon content was the opposite; the δ¹³C of SIC in the 0–20 and 60–80 cm soil layers were the highest in the 10a continuous cotton field soil, which were −22.24 and −21.86‰, respectively, and significantly different to other types (p < 0.05). The fixed carbon values in the barren, 5a, 10a, 20a, and 30a continuous cotton fields were 0.53, 0.17, 0.11, 0.13 and 0.33 g·kg⁻¹, respectively; the corresponding amounts of CO₂ fixed from soil respiration were 0.33, 0.11, 0.08, 0.05, and 0.25 g·kg⁻¹; the amounts of CO₂ from the atmosphere were 0.20, 0.06, 0.03, 0.02, and 0.09 g·kg⁻¹; and the oxidative decomposition of CO₂ by SOC were 0.17, 0.06, 0.04, 0.26, and 0.12 g·kg⁻¹, respectively, indicating that the contribution of SOC was more in the barren field and 30a cotton field. Comparing the sources of fixed CO₂, we found that the amount of fixed soil from barren fields and 30a was high from atmospheric CO₂, while the contribution of SOC was low. Furthermore, the amount of fixed CO₂ of 20a from SOC was high, and the atmospheric contribution was low. The main physicochemical factors that affecting the amount of soil SOC changed to SIC were soil water content, readily available carbon dioxide, and microbial biomass carbon. Full article

As an important part of the global carbon cycle, dissolved inorganic carbon (DIC) concentration and its stable carbon isotopic composition (δ¹³C_DIC) have been used to constrain the sources of DIC in rivers. In this study, we systematically investigated the water chemistry, DIC contents, and δ¹³C_DIC values in a tropical agricultural river in northeast Thailand. The water temperature ranged from 20.3 to 31.3 °C, and water pH values ranged from 6.4 to 8.4, with seasonal variations. Based on the major ion compositions, the hydro-chemical type of the Mun River water was a unique Na–Ca–Cl–HCO₃ type, controlled by evaporite and silicate weathering. Seasonal variation of DIC concentrations and its carbon isotopic composition was obvious; DIC and δ¹³C_DIC were significantly lower in the wet season (135 to 3146 μmol/L and −31.0‰ to −7.0‰) compared to the dry season (185 to 5897 μmol/L and −19.6‰ to −2.7‰). A high level of ¹²C-enriched DIC/CO₂ from soil respiration and organic matter oxidation may cause the low pH values, δ¹³C_DIC values, and high partial pressure of CO₂ (pCO₂) in the middle and lower reaches during the wet/rainy season compared to the dry season. This may be responsible for the seasonal and spatial variations of DIC concentrations and δ¹³C_DIC values in the Mun River. According to the relationship between pCO₂ and δ¹³C_DIC values, CO₂ outgassing may be more significant in the dry season, due to the greater influx of groundwater with higher pCO₂ levels; and the rapid CO₂ diffusion into the atmosphere will continuously increase the δ¹³C_DIC values and decrease pCO₂ levels. These results show that riverine biologic effects and CO₂ outgassing play important roles in the DIC and δ¹³C_DIC evolution of this typical agriculturally-dominated watershed. Full article

Pedogenic carbonate samples collected from three Lower Cretaceous (Aptian–Albian) fossil localities in Texas and Oklahoma were analyzed to develop paleoatmospheric pCO₂ estimates by measuring the stable carbon isotopes of pedogenic calcite and their co-existing occluded organic matter. Calcite δ¹³C values ranged from −10.9‰ to −4.4‰ while occluded organic matter δ¹³C values ranged from −27.3‰ to −21.1‰. These stable carbon isotope measurements combined with temperature (30 °C) and soil-respired CO₂ concentration (839–6047 ppmV) values provided atmospheric pCO₂ estimates ranging from 67 ppmV to over 1100 ppmV. These estimates show a significant increase in atmospheric pCO₂ during the late Aptian followed by a decrease in atmospheric pCO₂ during the late Aptian to early Albian transition period, roughly correlating with the OEA1b event. Given the lack of chronostratigraphic constraints of the Lower Cretaceous geologic units in the study area, these data provide further evidence for the approximate age of the units as well as pertinent paleoclimate insights into greenhouse climate conditions. Full article

Bioenergy crops such as Miscanthus × giganteus are foreseeable as an alternative source to replace fossil fuel and reduce greenhouse gas emissions. They are also assessed as an environment-friendly solution for polluted, marginal and low-quality agricultural soils. Several studies had been launched on soil organic carbon sequestration potentials of miscanthus culture along with its impacts on restoring soil functionality, most of which focus on the long-term basis of the plant’s cultivation. Nevertheless, information concerning the short term impacts as well as the situation in Czechia is still scarce. In this context, a field experiment was launched in 2017 in a poor-quality agricultural land in the city of Chomutov (North-Western Czechia) to compare the impacts of the perennial C₄ miscanthus with an annual C₃ forage crop (wheat) on the soil carbon stocks as well as enhancing its functionality. Results through the 0–30 cm soil profile examination showed that miscanthus plants played a role in improving the studied soil physico-chemical (bulk density and soil organic carbon concentrations) and biological (Phospholipid fatty acids stress indicator, basal respiration and fluorescein diacetate hydrolytic activity) parameters. The naturally occurring δ¹³C concentrations were used to evaluate the direct plant contribution to the total soil organic carbon (SOC) stocks and revealed considerable miscanthus contribution all over the detected soil layers (1.98 ± 0.21 Mg C. ha⁻¹ yr⁻¹) after only 3 growing seasons. It is thus suggested that the C₄ perennial miscanthus possess remarkable prospects for SOC sequestration and restoring degraded lands. Full article

Carbon (C) isotope discrimination during photosynthetic CO₂ assimilation has been extensively studied, but the whole process of fractionation from leaf to soil has been less well investigated. In the present study, we investigated the δ¹³C signature along the C transfer pathway from air to soil in a coniferous and broad-leaved mixed forest in northeast China and examined the relationship between δ¹³C of respiratory fluxes (leaf, trunk, soil, and the entire ecosystem) and environmental factors over a full growing season. This study found that the δ¹³C signal of CO₂ from canopy air was strongly imprinted in the organic and respiratory pools throughout C transfer due to the effects of discrimination and isotopic mixing on C assimilation, allocation, and respiration processes. A significant difference in isotopic patterns was found between conifer and broadleaf species in terms of seasonal variations in leaf organic matter. This study also found that δ¹³C in trunk respiration, compared with that in leaf and soil respiration, was more sensitive to seasonal variations of environmental factors, especially soil temperature and soil moisture. Variation in the δ¹³C of ecosystem respiration was correlated with air temperature with no time lag and correlated with soil temperature and vapor pressure deficit with a lag time of 10 days, but this correlation was relatively weak, indicating a delayed linkage between above- and belowground processes. The isotopic linkage might be confounded by variations in atmospheric aerodynamic and soil diffusion conditions. These results will help with understanding species differences in isotopic patterns and promoting the incorporation of more influencing factors related to isotopic variation into process-based ecosystem models. Full article