Soil CO2 Research Articles

Large Offsets in the Impacts Between Enhanced Atmospheric and Soil Water Constraints and CO2 Fertilization on Dryland Ecosystems

Greening dryland ecosystems greatly benefits from significant CO2 fertilization. This greening trend across global drylands, however, has also been severely constrained by enhancing atmospheric and soil water (SW) deficits. Thus far, the relative offsets in the contributions between the atmospheric vapor pressure deficit (VPD), SW at varying depths, and CO2 fertilization to vegetation dynamics, as well as the differences in the impacts of decreasing SW at different soil depths on dryland ecosystems over long periods, remain poorly recorded. Here, this study comprehensively explored the relative offsets in the contributions to vegetation dynamics between high VPD, low SW, and rising CO2 concentration across global drylands during 1982–2018 using process-based models and satellite-observed Leaf Area Index (LAI), Gross Primary Productivity (GPP), and solar-induced chlorophyll fluorescence (SIF). Results revealed that decreasing-SW-induced reductions of LAI in dryland ecosystems were larger than those caused by rising VPD. Furthermore, dryland vegetation was more severely constrained by decreasing SW on the subsurface (7–28 cm) among various soil layers. Notable offsets were found in the contributions between enhanced water constraints and CO2 fertilization, with the former offsetting approximately 38.49% of the beneficial effects of the latter on vegetation changes in global drylands. Process-based models supported the satellite-observed finding that increasing water constraints failed to overwhelmingly offset significant CO2 fertilization on dryland ecosystems. This work emphasizes the differences in the impact of SW at different soil depths on vegetation dynamics across global drylands as well as highlights the far-reaching importance of significant CO2 fertilization to greening dryland ecosystems despite increasing atmospheric and SW constraints.

Soil CO2 efflux response to two decades of altered carbon inputs in a temperate coniferous forest

Global soils play a critical role in carbon (C) cycling and storage, and even minor disturbances to soil C flux can cause CO2 release to the atmosphere, exacerbating the greenhouse effect. This study investigates the long-term effects of forest detrital manipulation on soil CO2 efflux at a temperate forest site in Oregon’s western Cascade Mountains. We assessed the variation in seasonal and diurnal autotrophic and heterotrophic contributions to in situ soil CO2 efflux after 25 + years of detritus additions and removals and found slight increases in soil CO2 efflux rates concurrent with slight increases in soil C stocks, relative to C input rates, that may reflect underlying changes to C cycling in this system resulting from sustained detritus manipulation coupled with environmental change. Total CO2 efflux experienced increased contributions from functionally autotrophic root and rhizosphere respiration relative to the heterotrophic component. Seasonal and diurnal differences between soil respiration rates by treatment suggest a soil moisture buffering effect provided by the extra woody detritus that may support vegetative growth at times when seasonal drought would ordinarily slow plant and soil microbial metabolic activity. Overall, this research highlights the long-term effects of sustained litter additions and removals on soil CO2 efflux, which can help illuminate the response of C cycling in forests to current and future global change.

A portable low‐cost incubation chamber for real‐time characterization of soil respiration

AbstractMonitoring CO2 or O2 concentrations within a closed, volume‐defined chamber is widely used to quantify soil respiration during laboratory soil incubation experiments. The standard method of using periodic manual gas sampling is costly, labor‐intensive, and frequently fails to capture the aerobic respiration process. Thus, tools that allow continuous, real‐time tracking of CO2 and O2 concentration changes are needed for soil respiration research. This study presents a new, portable, low‐cost (∼$700), open‐source sensor system to measure CO2 and O2 concentrations in four closed chambers. We provided non‐engineering end‐users with step‐by‐step instructions on how to build the system, enabling replication and customization. System performance was tested by comparing two respiration rates using the same soil—soil with and without glucose added for 1 week. Consistent CO2 production and O2 consumption rates were measured at 1‐min intervals, and the reliability of the system was validated by a trace gas analyzer. Two distinctive continuous apparent respiratory quotient time series between two soil treatments were observed, with higher values of CO2 in glucose soil, demonstrating the ability of the system to capture ongoing respiration processes and sufficient sensitivity to distinguish differences among respiration substrates (i.e., glucose). The tested performance of the system highlights its capabilities for soil respiration research and the potential for further adoption in real‐time gas monitoring applications.

Effects of Mercury Pollution on Soil Organic Carbon Stability and Carbon-fixing Microbial Communities

To elucidate the effects of Hg pollution on soil organic carbon stability and autotrophic microbial carbon assimilation, the characteristics of soil CO2 emission rate, organic carbon components, and cbbL and cbbM functional microorganisms before and after 29 d of Hg pollution were studied using indoor culture experiments and molecular biology techniques. The results showed that the effects of different levels of Hg pollution on soil CO2 emission rates were different. High levels of Hg （S2,S3,and S5） inhibited soil CO2 cumulative emissions, whereas low levels of Hg （S1,S4,and S6） promoted soil carbon emissions. Hg pollution affected the proportion of soil organic carbon components. The changes in SOC and MBC contents in different treatments were basically the same, with significant differences （P < 0.05）. EOC and DOC decreased with the increase in Hg content. Compared with that at 1 d, the qCO2 of each treatment was significantly decreased at the end of culture （P < 0.05）. The effects of different levels of Hg pollution on the functional microbial communities of cbbL and cbbM were significantly different. Proteobacteria, Actinobacteria, and Acidobacteria were the dominant phyla shared by the two functional microorganisms. Cumulative soil CO2 emissions and SOC were the main factors affecting the change in the cbbL community, and soil available Hg was the main factor affecting the change in the cbbM community. In summary, the results of this study can provide a theoretical basis for the carbon cycle and accumulation of Hg-contaminated regional ecosystems.

Thermal Adaptation of Enzyme‐Mediated Processes Reduces Simulated Soil CO2 Fluxes Upon Soil Warming

AbstractUnderstanding factors influencing carbon effluxes from soils to the atmosphere is important in a world experiencing climatic change. Two important uncertainties related to soil organic carbon (SOC) stock responses to a changing climate are (a) whether soil microbial communities acclimate or adapt to changes in soil temperature and (b) how to represent this process in SOC models. To further explore these issues, we included thermal adaptation of enzyme‐mediated processes in a mechanistic SOC model (ReSOM) using the macromolecular rate theory. Thermal adaptation is defined here to encompass all potential responses of soil microbes and microbial communities following a change in temperature. To assess the effects of thermal adaptation of enzyme‐mediated processes on simulated SOC losses, ReSOM was applied to data collected from a 13‐year soil warming experiment. Results show that a model omitting thermal adaptation of enzyme‐mediated processes substantially overestimates observed CO2 effluxes during the initial years of soil warming. The bias against observed CO2 effluxes was lower for models including thermal adaptation of enzyme‐mediated processes. In addition, for a simulated linear 3°C soil warming over 100 years, models including thermal adaptation of enzyme‐mediated processes simulated SOC losses of a factor of three smaller than models omitting this process. As thermal adaptation of microbial community characteristics is generally not included in models simulating feedback between the soil, biosphere and atmosphere, we encourage future studies to assess the potential impact that microbial adaptation has on soil carbon – climate feedback representations in models.

Is soil contamination a missing driver of soil heterotrophic respiration in land surface models? A study case with copper –

Land Surface Models (LSMs) are crucial elements of Earth System Models used to estimate the effects of anthropogenic greenhouse gas (GHG) emissions on Earth's climate. Nevertheless, as well as land use change and direct GHG emissions, anthropogenic activities are also associated with contaminant emissions and depositions. Although contamination has a recognized impact on soil processes such as GHG emissions, soil contamination is currently not considered as an important process to consider into LSMs.In this study we hypothesized that soil contamination has significant impact on soil CO2 emissions such as heterotrophic respiration (Rh). To this end, we analyzed how soil contamination may account for residuals of modeled Rh from 11 LSMs as compared to Rh products derived from observations over Europe. We used generalized least squared mixed models to evaluate the primary factors driving of the model residuals. Among contaminants, we focused on copper (Cu), which is widely used in industry or agriculture, causing significant diffuse contamination. Additionally, research demonstrated a strong correlation between soil Rh and Cu availability to soil fauna and various soil pedological and climatic parameters. Hence, we completed our analysis by including pedo-environmental parameters and by analyzing Rh against a proxy of bioavailable Cu.Our findings indicate that Cu is a non-negligible variable in explaining the Rh models inaccuracy considering either total or free Cu forms. Therefore, it can be concluded that Cu should not be disregarded as a key factor in predicting Rh.

The Dynamic Characteristics and Influencing Factors of Soil Respiration in Different Types of Grasslands in the Barkol Lake Basin

Determining regional and global carbon cycles hinges on investigating the dynamic characteristics and influencing factors of soil respiration in various types of natural grasslands located in arid regions, and these characteristics are important indicators for assessing the structural and functional health of grassland ecosystems. Such investigations also provide theoretical support for carbon sink monitoring, energy conservation, emission reduction and low-carbon development in the western arid zone and are important for obtaining an in-depth understanding of the carbon cycle, as well as for ecosystem management, restoration and the reconstruction of arid areas. In this study, during the growing season (from May to October) of 2022, the LI-8100A automated soil CO2 flux system was used to measure the soil respiration rate (Rs), temperature from 1.5 m above the surface to depths of 5–25 cm (T, T5, T10, T15, T20 and T25) and the soil moisture content (SM) at a depth of 20 cm in four types of grasslands: lowland meadow, alpine meadow, temperate desert steppe and temperate steppe desert. Five replicates were established for each plot, and the responses of Rs to T and SM were fitted to construct the optimal regression model. The results revealed that (1) the daily average soil respiration was highest in the lowland meadow (0.07 to 5.76 μmol·m−2·s−1), followed by the alpine meadow (−0.57 to 0.95 μmol·m−2·s−1), the temperate desert steppe (−0.45 to 3.0 μmol·m−2·s−1) and the temperate steppe desert (−1.29 to 1.61 μmol·m−2·s−1); (2) the soil respiration rates of the four grassland types were significantly correlated with the temperature in the 5–15 cm soil layer, and the best model was an exponential function; the peak values generally appeared between 13:00 and 17:00 (h), with the minimum values at 2:00 or 8:00 (h); the maximum value was observed in July–August, and the minimum value was observed in October; and the soil respiration in the lowland meadow was higher than that in the other three types of grassland during the same period. The average variation intensities of the soil respiration from May to October were as follows: temperate steppe desert (91.78%) > temperate desert steppe (76%) > alpine meadow (58.77%) > lowland meadow (43.93%). (3) The partial correlation analysis revealed that when soil temperature was used as a control, the correlation between SM and soil respiration in the four types of grasslands changed, and the coefficient of determination (R2) increased to varying degrees, explaining up to 80% of the variation in the soil respiration in the lowland meadows. The correlation between soil respiration and the SM normalized to 10 °C explained up to 93.8% of the variation in soil respiration; the two-factor fitting equations revealed that the model with soil temperature and SM was superior to the single-factor model with either soil temperature or SM.

Freeze–Thaw Events Change Soil Greenhouse Gas Fluxes Through Modifying Soil Carbon and Nitrogen Cycling Processes in a Temperate Forest in Northeastern China

Freeze–thaw events are predicted to be more frequent in temperate forest ecosystems. Whether and how freeze–thaw cycles change soil greenhouse gas fluxes remains elusive. Here, we compared the fluxes of three soil greenhouse gases (CO2, CH4, and N2O) across the spring freeze–thaw (SFT) period, the growing season (GS), and the annual (ALL) period in a temperate broad-leaved Korean pine mixed forest in the Changbai Mountains in Jilin Province, Northeastern China from 2019 to 2020. To assess the mechanisms driving the temporal variation of soil fluxes, we measured eleven soil physicochemical factors, including temperature, volumetric water content, electrical conductivity, gravimetric water content, pH, total carbon, total nitrogen, total-carbon-to-total-nitrogen ratio, nitrate (NO3−), ammonium (NH4+), and dissolved organic carbon, all of which play crucial roles in soil carbon (C) and nitrogen (N) cycling. Our findings indicate that the soil in this forest functioned as a source of CO2 and N2O and as a sink for CH4, with significant differences in greenhouse gas (GHG) fluxes among the SFT, GS, and ALL periods. Our results suggest freeze–thaw events significantly but distinctly impact soil C and N cycling processes compared to normal growing seasons in temperate forests. The soil N2O flux during the SFT (0.65 nmol m−2 s−1) was 4.6 times greater than during the GS (0.14 nmol m−2 s−1), likely due to the decreased NO3− concentrations that affect nitrification and denitrification processes throughout the ALL period, especially at a 5 cm depth. In contrast, soil CO2 and CH4 fluxes during the SFT (0.69 μmol m−2 s−1; −0.61 nmol m−2 s−1) were significantly lower than those during the GS (5.06 μmol m−2 s−1; −2.34 nmol m−2 s−1), which were positively influenced by soil temperature at both 5 cm and 10 cm depths. Soil CO2 fluxes increased with substrate availability, suggesting that the total nitrogen content at 10 cm depth and NH4+ concentration at both depths were significant positive factors. NO3− and NH4+ at both depths exhibited opposing effects on soil CH4 fluxes. Furthermore, the soil volumetric water content suppressed N2O emissions and CH4 oxidation, while the soil gravimetric water content, mainly at a 5 cm depth, was identified as a negative predictor of CO2 fluxes. The soil pH influenced CO2 and N2O emissions by regulating nutrient availability, particularly during the SFT period. These findings collectively contribute to a more comprehensive understanding of the factors driving GHG fluxes in temperate forest ecosystems and provide valuable insights for developing strategies to mitigate climate change impacts.

CO2 Emission from Caves by Temperature-Driven Air Circulation—Insights from Samograd Cave, Croatia

Opposite to atmospheric CO2 concentrations, which reach a minimum during the vegetation season (e.g., June–August in the Northern Hemisphere), soil CO2 reaches a maximum in the same period due to the root respiration. In karst areas, characterized by high rock porosity, this excess CO2 seeps inside caves, locally increasing pCO2 values above 1%. To better understand the role of karst areas in the carbon cycle, it is essential to understand the mechanisms of CO2 dynamics in such regions. In this study, we present and discuss the spatial and temporal variability of air temperature and CO2 concentrations in Samograd Cave, Croatia, based on three years of monthly spot measurements. The cave consists of a single descending passage, resulting in a characteristic bimodal climate, with stable conditions during summer (i.e., stagnant air inside the cave) and a strong convective cell bringing in cold air during winter. This bimodality is reflected in both CO2 concentrations and air temperatures. In summer, the exchange of air through the cave’s main entrance is negligible, allowing the temperature and CO2 concentration to equilibrate with the surrounding rocks, resulting in high in-cave CO2 concentrations, sourced from enhanced root respiration. During cold periods, CO2 concentrations are low due to frequent intrusions of fresh external air, which effectively flush out CO2 from the cave. Both parameters show distinct spatial variability, highlighting the role of cave morphology in their dynamics. The CO2 concentrations and temperatures have increased over the observation period, in line with external changes. Our results highlight the role of caves in transferring large amounts of CO2 from soil to the atmosphere via caves, a process that could have a large impact on the global atmospheric CO2 budget, and thus, call for a more in-depth study of these mechanisms.

Soil respiration related to the molecular composition of soil organic matter in subtropical and temperate forests under soil warming

The chemical composition and degradability of soil organic matter (SOM) are among the most important factors influencing the feedback between soil CO2 emissions and climate warming. We hypothesized that the response of soil respiration to long-term warming in various forest ecosystems depends on how soil warming alters the chemical composition of SOM. Therefore, we compared the effects of long-term soil warming on soil respiration, SOM molecular structure, and bacterial and fungal diversity in two forest ecosystems in the southern subtropical and warm temperate zones of China. In the subtropical forest, soil warming did not affect soil respiration in the short term (2–3 years) but decreased it in the longer term (10 years, −10%). The decline in soil respiration was associated with an increased aliphaticity of SOM and lower O-alkyl C content, along with an increased abundance of microbial K-strategists over time. In the warm temperate forest, soil warming significantly stimulated soil respiration by 35% in the short term and 30% in the long term. The sustained positive response to warming was likely related to the increased decomposability of SOM owing to increased root C input. Our results suggest that the molecular composition of SOM is affected by warming and in turn feeds back to longer-term soil respiration responses. The different responses at the two study sites suggest considerable variation in the feedback within different forest ecosystems.

Effects of intercropping with legume forage on the rhizosphere microbial community structure of tea plants.

Intercropping in agriculture is crucial for addressing challenges in intensive tea farming. Forage legumes reduce fertilizer dependence and significantly boost productivity. Currently, intercropping with legumes enhances the environmental conditions of tea plantations and improves tea quality. However, the comprehension of the rhizosphere's impact on the associated microbes and the community structure of tea plants is still somewhat constrained. Hence, four distinct planting methodologies were examined: Monoculture cultivation of Tieguanyin tea plants (MT), Laredo forage soybean (Glycine max Linn.) without partitioning in conjunction with tea (IT), intercropping with tea using plastic partitions (PPIT), and intercropping with tea facilitated by net partitions (NPIT). An absolute quantitative analysis of soil phospholipid fatty acids, labeled with the rhizosphere microbial characteristics of tea plants, was conducted through multi-ion reaction monitoring (MRM). The bacterial and fungal communities were anticipated utilizing the FAPROTAX and FUNG databases, respectively. Gas chromatography was employed to ascertain greenhouse gas emissions across diverse root interaction cultivation systems. The rhizospheric influence culminated in a 44.6% increase in total phospholipid fatty acids (PLFAs) and a remarkable 100.9% escalation in the ratio of unsaturated to saturated fatty acids. This rhizospheric enhancement has significantly potentiated the ecological functionalities within the bacterial community, including xylanolysis, ureolysis, nitrogen respiration, nitrogen fixation, nitrite respiration, nitrite ammonification, and nitrate reduction. Mycorrhizomonas, encompassing both ectomycorrhizal and arbuscular forms, has notably colonized the rhizosphere. The interspecific mutualistic interactions within the rhizosphere have resulted in a significant enhancement of plant growth-promoting bacteria, including allorhizobium, bradyrhizobium, rhizobium, burkholderia, gluconacetobacter, and gluconobacter, while concurrently reducing the prevalence of pathogenic microorganisms such as xanthomonas, ralstonia, fusarium, and opportunistic fungi responsible for white and soft rot. The intercropping system showed lower total greenhouse gas emissions than monocultured tea plants, particularly reducing soil CO2 emissions due to complex interspecific rhizosphere interactions. This tea/legume intercropping approach promotes a sustainable ecosystem, enhancing microbial biomass and vitality, which helps suppress rhizospheric pathogens. These findings are instrumental in enhancing our comprehension of the pivotal practical implications of rhizosphere intercropping, thereby optimizing the structure of rhizosphere communities and alleviating the impact of greenhouse gases within croplands.

Effects of nitrogen fertilizer and biochar levels on soil CO2 emission and wheat yield in irrigation region

Effects of nitrogen fertilizer and biochar levels on soil CO2 emission and wheat yield in irrigation region

Estimation of Soil Carbon Balance Based on СО<sub>2</sub> Emission Determination

The increased interest nowadays in quantitative assessment of soil respiration is largely due to studies of the role of various terrestrial ecosystems in changing the concentration of the most important greenhouse gas, CO2, in the atmosphere. The review considers methodological aspects of determining the actual CO2 emission from soils using chamber and absorption methods, as well as the use of the obtained data to assess the carbon balance in soils. Successful development of this topic will allow to promptly get an answer to the main question of this pressing environmental issue: what is the soil of this or that ecosystem for atmospheric CO2 – a net source or a net sink? The article analyzes the results of works devoted to comparative determination of CO2 emission from soils by these methods. It is shown that the widespread opinion about obtaining underreported data by absorption method is often based on studies in which the basic principles of the method were violated. It is concluded that it is necessary to carry out in-depth comparative studies on determination of average daily indicators of CO2 emission from soil by chamber and absorption methods. It is recognized that, regardless of the method, the main problem in using CO2 production data to estimate soil C balance is the adequate partitioning of total respiration into heterotrophic and autotrophic components, the ratio between which varies widely depending on soil and vegetation conditions. Due to imperfection and labor intensity of existing methods, this division can cause significant errors in determining the annual mineralization of soil organic matter. To reduce them, the approach to determination of mineralization losses of CO2 in bare fallow soils is considered. It is natural for soils of agrocenoses, but as a methodological technique can probably be used in natural grass ecosystems as well. Reduction of errors can be ensured due to the fact that differences in actual mineralization of organic matter in bare fallow and plant-occupied soils are several times less than changes in the ratio between heterotrophic and autotrophic components of soil respiration in different biogeocenoses.

Assessment of soil CO2, CH4, and N2O fluxes and their drivers, and their contribution to the climate change mitigation potential of forest soils in the Lublin region of Poland

AbstractForests can play a key role in the mitigation of climate change, although there have been limited regional scale assessments that account for variations in soil type and tree species. Most of the focus has been on their ability to sequester atmospheric CO2, while there is less information on the two other major greenhouse gases (GHGs), N2O and CH4. We examined the GHG budgets of ten forest soils in Poland, considering all three major GHGs, where no previous long-term measurements had been made, which encompassed different tree species, stand age, and contrasting edaphic conditions. In addition to the quantification and assessment of seasonal variability in the major soil GHG fluxes over two years, the aims of the present study were (i) the identification of the main drivers of the soil-based GHG fluxes, (ii) the determination of the contribution of each gas to the Global Warming Potential (GWP), and (iii) to assess the mitigation potential of these fluxes over different forest systems. All the forest soils were sources of CO2 and N2O and sinks for atmospheric CH4 with pronounced seasonal variations in CO2 and CH4 driven by soil moisture and temperature. The soils showed significant differences in annual GHG fluxes, with average values of 16.7 Mg CO2 ha−1, − 3.51 kg CH4 ha−1, and 0.95 kg N2O ha−1. The annual total GWP ranged from 13.1 to 22.0 Mg CO2 eq ha−1 with CO2 making the highest contribution, and forest-specific CH4 uptake resulting in a reduction in GWP, ranging from − 0.08% (in the youngest forest) to -0.97% (in the oldest forest). Mixed forests showed the greatest potential for climate change mitigation, with the highest soil C sequestration, and the lowest GWP values when compared to sites with monocultures. The results suggest that a mixture of tree species could eventually be incorporated into management plans to increase the effectiveness of forests in climate change mitigation.

Spatial Variability of Soil CO2 Emissions and Microbial Communities in a Mediterranean Holm Oak Forest

Forests play a key role in the global carbon (C) cycle through multiple interactions between above-ground and soil microbial communities. Deeper insights into the soil microbial composition and diversity at different spatial scales and soil depths are of paramount importance. We hypothesized that in a homogeneous above-ground tree cover, the heterogeneous distribution of soil microbial functional diversity and processes at the small scale is correlated with the soil’s chemical properties. From this perspective, in a typical Mediterranean holm oak (Quercus ilex L.) peri-urban forest, soil carbon dioxide (CO2) emissions were measured with soil chambers in three different plots. In each plot, to test the linkage between above-ground and below-ground communities, soil was randomly sampled along six vertical transects (0–100 cm) to investigate soil physico-chemical parameters; microbial processes, measured using Barometric Process Separation (BaPS); and structural and functional diversity, assessed using T-RFLP and qPCR Real Time analyses. The results highlighted that the high spatial variability of CO2 emissions—confirmed by the BaPS analysis—was associated with the microbial communities’ abundance (dominated by bacteria) and structural diversity (decreasing with soil depth), measured by H′ index. Bacteria showed higher variability than fungi and archaea at all depths examined. Such an insight showed the clear ecological and environmental implications of soil in the overall sustainability of the peri-urban forest system.

CO₂ sequestration and soil improvement in enhanced rock weathering: A review from an experimental perspective

AbstractEnhanced rock weathering (ERW) is an emerging negative emission technology (NET) with significant potential for mitigating climate change and improving soil health through the accelerated chemical weathering of silicate minerals. This study adopts a critical research approach to review existing ERW experiments, focusing on the mechanisms of soil improvement and CO₂ sequestration, as well as the economic costs and environmental risks associated with its large‐scale implementation. The results demonstrate that while ERW effectively enhances soil pH and provides essential nutrients for crops, its CO₂ sequestration capacity is highly dependent on variables such as soil type, rock type, application rate, and particle size. Furthermore, the economic feasibility of ERW is challenged by high costs related to mining, grinding, and transportation, and environmental risks posed by the release of heavy metals like Ni and Cr during the weathering process. Notably, significant discrepancies exist between laboratory experiments and field applications, highlighting the need for extensive in‐situ monitoring and adjustment of ERW practices. This study underscores the importance of optimizing ERW strategies to maximize CO₂ sequestration while minimizing environmental impacts. Future research should focus on long‐term field experiments, understanding secondary mineral formation, and refining the application techniques to enhance the overall efficiency and sustainability of ERW. © 2024 Society of Chemical Industry and John Wiley & Sons, Ltd.

Effects of Irrigation Amount and Salinity Levels on Maize (Zea mays L.) Growth, Water Productivity and Carbon Emissions in Arid Region of Northwest China

To address the growing scarcity of freshwater resources, the use of saline water for agricultural irrigation is gaining increasing attention. This study presents findings from a two-year field experiment conducted during the 2023 and 2024 maize-growing seasons in northwestern China. The objective of the experiment was to evaluate the main and interactive effects of saline irrigation water on soil water–salt dynamics, maize growth, photosynthetic characteristics, water productivity, and carbon emissions. The experiment involved nine treatments with three irrigation amounts: 4500 m3 hm−2 (W1), 5625 m3 hm−2 (W2), and 6750 m3 hm−2 (W3), combined with three water salinity levels: 0.85 g L−1 (S1, freshwater), 3 g L−1 (S2), and 5 g L−1 (S3). Results indicated that both irrigation amount and salinity level significantly affected water–salt dynamics, with more soil accumulating in the 0–100 cm soil layer under saline irrigation water; however, this effect diminished with higher irrigation amounts. The maximum leaf area index and plant height were affected by both the irrigation amount and salinity level, as well as their interaction. Photosynthetic capacity declined with increasing salinity of the irrigation water, ultimately reducing grain yield and irrigation water use efficiency. Compared to freshwater (S1), the average maize grain yield under S2 and S3 treatments decreased by 6.28% and 15.43% in 2023 and by 7.82% and 17.48% in 2024, respectively. Additionally, for the same irrigation amount, higher salinity of the irrigation water (S2, S3) significantly reduced total soil CO2 emissions, with reductions of 10.08% and 27.53% in 2023, and 11.97% and 28.01% in 2024, respectively. In summary, to optimize the utilization of saline water, enhance maize yield, and improve soil carbon sequestration, we recommend maintaining the salinity of irrigation water below 3 g L−1, and using an irrigation amount of 6750 m3 hm−2 (W3S2) for optimal outcomes in the study area.

Forest soil CO2 emission in Quercus robur level II monitoring site

Abstract In this study, the soil CO2 emission was analysed at the level II ICP Forests monitoring plot in Serbia in the pedunculate oak forest. Two plots of pedunculate oak (Quercus robur L.) were selected for this study. The main question was to determine the differences in the impact of management (human impact) on CO2 emission. Different time periods were compared to identify the main factors affecting soil CO2 emission. Sampling was done by chambers. During the study period, climate indicators were quite different. A strong positive correlation between the soil temperature and soil CO2 emission, as well as a strong negative correlation between the soil moisture and soil CO2 emission, was found in the spring aspect (Plot). In other cases, a moderate to weak correlation was found. Multiple linear regressions showed that CO2 emission from soil was primarily controlled by soil moisture. Increasing soil water content had a positive effect on soil respiration (except in spring). The effect of soil temperature appeared in the multiple regressions as a secondary factor during the period studied, and an increase in temperature resulted in a decrease in soil respiration (except in spring).

Stable isotopic evidence for increased terrestrial productivity through geological time

Marine life on Earth is known back to the Archean Eon, when life on land is assumed to have been less pervasive than now. Precambrian life on land can now be tested with stable isotopes because living soil CO2 is isotopically distinct for both carbon and oxygen from both marine and volcanic CO2. Our novel compilation of previously published oxygen and carbon isotopic compositions of pedogenic and paleokarst carbonate can be compared with the coeval marine record. Long-term enrichment (to heavier isotopic composition) of oxygen, but no significant trend in carbon through time, long apparent from marine carbonate, is now demonstrated also for pedogenic and paleokarst carbonate. Oxygen isotopic enrichment is not due to changing global temperature or hypsometry, but to increased evapotranspiration and photosynthesis on larger continents. Differences in isotopic composition between land and sea have increased in an episodic fashion, peaking at times of major evolutionary innovations for life on land, and also at times of ice ages. The δ13C and δ18O divergences between land and sea correspond to terrestrial productivity spikes including evolution of Neoproterozoic (635 Ma) lichens, middle Ordovician (470 Ma) non-vascular land plants, middle Devonian (385 Ma) forests, early Cretaceous (125 Ma) angiosperms, and middle Miocene (20 Ma) sod grasslands.

Multidisciplinary high resolution Geophysical Imaging of Pantano Ripa Rossa Segment of the Irpinia Fault (Southern Italy)

The Irpinia Fault, also known as the Monte Marzano Fault System, located in the Southern Apennines (Italy), is one of the most seismically active structures in the Mediterranean. It is the source of the 1980, Ms 6.9, multi-segment rupture earthquake that caused significant damage and nearly 3,000 casualties. Paleoseismological surveys indicate that this structure has generated at least four Mw ~ 7 surface-rupturing earthquakes in the past 2 ka. This paper presents a comprehensive, high-resolution geophysical investigation focused on the southernmost fault segment of the Monte Marzano Fault System, i.e., the Pantano-Ripa Rossa Fault, outcropping within the Pantano di San Gregorio Magno intramontane basin. The project, named TEst Site IRpinia fAult (TESIRA), was supported by the University of Napoli Federico II to study the near-surface structure of this intra-basin fault splay that repeatedly ruptured co-seismically in the past thousands of years. Our imaging approach included 2D and 3D electrical and seismic surveys, gravimetry, 3D FullWaver electrical tomography, drone-borne GPR and magnetic surveys, and CO2 soil flux assessment across the surface rupture. This multidisciplinary investigation improved our understanding of the basin shallow structure, providing an image of a rather complex subsurface fault and basin geometry. Seismic data suggest that fault activity at the Pantano segment of MMFS is characterized by a near-surface cumulative displacement greater than previous estimations, calling into question earlier assumptions about the timing of its activation. Despite some challenges with our drone-mounted survey equipment, the integrated dataset provides a comprehensive and reliable image of the subsurface structure. This work demonstrates the utility of developing an integrated approach at high-resolution geophysical imaging and interpretation of fault zones with weak morphological expressions.