Soil CO2 Concentration Research Articles

The effect of microorganisms on soil carbonate recrystallization and abiotic CO2 uptake of soil

Desert ecosystems with a high soil pH are considered as a sink for atmospheric CO2. Although high CO2-uptakevia chemical processes is the major CO2-uptake process in saline and alkaline soil, microorganisms may affect the exchange of inorganic carbon between the soil solution and the solid phase. Some studies related to microbial processes on carbonate formation have been published, but seldom focus on saline and alkaline soils. To determine the microbial effects on the inorganic C flux and CaCO3 recrystallization, sterile and non-sterile Solonchak samples were incubated in a 14CO2-labelled atmosphere at two CO2 concentrations (0.2% and 2%). The 14C activity was measured in the soil solution, air, and in CaCO3 after 2, 7, 21, 92 and 197 days. The 14C in dissolved organic carbon in the sterile and non-sterile soils was below 5% of the 14C input. 14C trapping in CaCO3 increased with the decrease of the 14C remaining in the gaseous CO2. Carbonate recrystallization increased logarithmically with time (R2 > 0.96). A two percent initial CO2 concentration lead to higher CaCO3 recrystallization (5–50 × 10−3% of initial CaCO3) compared to a 0.2% initial CO2 concentration (0.8–7 × 10−3% of initial CaCO3) from 2 to 197 days. CaCO3 recrystallization (% of initial CaCO3) in the sterile Solonchak was higher by 10% to 190% than the non-sterile Solonchak, indicating that the microorganisms decreased the 14C trapping of CaCO3 by 4–23% from 2 to 197 days. We assume that microorganisms grew on the carbonate surface like a coating. This must have retarded the carbonate recrystallization. We concluded that the soil CO2 concentration is the most important factor for CaCO3 recrystallization. The presence of microorganisms strongly decreased the CaCO3 recrystallization. CaCO3 recrystallization process including CO2 in soil water could be the abiotic CO2 uptake from the atmosphere by saline and alkaline soil.

Differential effects of wetting and drying on soil CO2 concentration and flux in near-surface vs. deep soil layers

Soil stores over 2500 Pg carbon (C), with the majority of C stored in deep soil layers (> 30 cm). Soil C can be lost to the atmosphere when organic compounds are mineralized to carbon dioxide (CO2, via oxidative decay or respiration) and moved upward through the soil profile (via diffusion). Soil moisture status can influence the balance between respiration and diffusion, thereby altering the soil CO2 concentration and flux. However, it is unclear how wetting and drying influence soil CO2 dynamics in surface vs. deep soil layers. Thus, we irrigated three soil profiles in Mediterranean arable land and continuously monitored soil CO2 concentration at 15, 30, 50, 70 and 90 cm during wetting and drying phases under ambient temperature conditions. We estimated gas diffusivity, CO2 flux, and temperature responses of soil CO2 concentration during the experiment. Decreases in gas diffusivity during the wetting period coincided with increases in soil CO2 concentrations. However, the negative gas diffusivity-soil CO2 concentration relationship did not hold true all the time, implying that CO2 production was the driving factor for the apparent soil CO2 concentration. We observed hysteretic responses of soil CO2 concentration to temperature as soil moisture varied, with deeper soil CO2 concentration being more sensitive to temperature than surface soil CO2 concentration, especially during the drying phase. The movement of CO2 was upward at all depths during the ambient phase, but the direction and the magnitude of CO2 fluxes varied across the depth gradient during the wetting and drying phases. This study highlights that the relative contribution of gas diffusivity vs. CO2 production to soil CO2 concentration changes with wetting and drying, and that the responses of soil CO2 concentration to temperature are dependent on the antecedent environmental conditions. Also, the downward movement of CO2 during the wetting and drying phases suggests that quantifying surface soil CO2 efflux may underestimate dynamic C processes in deeper soils.

Here comes the flood! Stress effects of continuous and interval waterlogging periods during the growing season on Scots pine saplings

Future climate scenarios for the boreal zone project increasing temperatures and precipitation, as well as extreme weather events such as heavy rain during the growing season. This can result in more frequent short-term waterlogging (WL) leading to unfavorable conditions for tree roots. In addition, it is decisive whether short-term WL periods during the growing season occur continuously or periodically. We assessed the effects of short-termed WL on 4-year-old Scots pine (Pinus sylvestris L.) saplings after shoot elongation started. Waterlogging (WL) lasted either continuously for 2.5weeks (ContWL) or noncontinuously for 5 weeks, consisting of three repeated 1-week-interval WL periods (IntWL). Both treatments resulted in the same duration of soil anoxia. We studied soil gases, root and shoot growth and physiology, and root survival probability and longevity during the experiment. In the final harvest, we determined shoot and root biomass and hydraulic conductance and electrical impedance spectra of the root systems. Soil CO2 and CH4 concentrations increased immediately after WL onset and O2 decreased until anoxia. Waterlogging decreased fine root survival probability, but there was no difference between WL treatments. Shoot growth suffered more from ContWL and root growth more from IntWL. Needle concentrations of pinitol increased in the WL saplings, indicating stress. No WL effects were observed in photosynthesis and chlorophyll fluorescence. Increased starch concentration in needles by WL may be due to damaged roots and thus a missing belowground sink. Electrical impedance indicated suffering of WL saplings, although root hydraulic conductance did not differ between the treatments. Oxidative stress of short-term and interval WL can have long-lasting effects on shoot and root growth and the physiology of Scots pine. We conclude that even short-term WL during the growing season is a stress factor, which will probably increase in the future and can affect carbon allocation and dynamics in boreal forests.

Measurement of Carbon Dioxide and Methane in Forest Soils Following Uncontrolled Wildfires in the Coconino National Forest

We have used a portable, battery-powered quadrupole mass spectrometer to measure the relative concentrations of carbon dioxide (CO2), methane (CH4), and water vapor in soils of the Coconino National Forest. In particular, we have compared the soil gas levels in regions of the forest that have been untouched with regions that have suffered wildfire damage. With some exceptions, our results tend to indicate that both the soil CO2 concentration and the soil CH4 concentrations decrease somewhat as the severity of the forest damage increases through the timing of the fire and subsequent forest regrowth. In some cases, soil water vapor content appears to have played a significant role in the concentrations of these gases as well. Further measurements over longer periods of time are required to more exactly quantify the role played by many different variables in the local concentrations of important forest soil gases.

Farmland degradation caused by radial diffusion of CO2 leakage from carbon capture and storage

Carbon capture and storage (CCS) may result in negative environmental impacts if CO2 escapes into the soil layer from deep geological storage formations. In particular, little is known about the spatial scope of possible impacts of CO2 leakages. This study designed and implemented a CO2 point-source shallow release experiment to simulate CCS leakage at a rate of 1.0 L min−1 and a depth of 1.5 m. The scope of crop and farmland responses to CO2 leakage were examined, with a focus on spring wheat. The experimental site had a radius of 9.0 m, and the leaked CO2 was found to influence soil CO2 concentrations up to 4.0 m from the source, or 2.67 times the depth of the leak. Furthermore, the influence radius of the CO2 leak on spring wheat height was about 1.0 m, which was 0.67 times the depth of the leak. The morphological characteristics of wheat observed directly above the leak were approximately 30–50% lower than the background levels (9.0 m from the source). CO2 leakage could therefore result in wheat field degradation along the soil surface. These findings suggest that a set of empirical parameters to assess the scope of the negative influence of CCS leakage on agriculture should be developed. Overall, the results indicate a concentric pattern of farmland and crop degradation with distance from the CCS leakage source, which may help to deepen understanding of the safety of CCS.

Dark microbial CO2 fixation in temperate forest soils increases with CO2 concentration.

Dark, that is, nonphototrophic, microbial CO2 fixation occurs in a large range of soils. However, it is still not known whether dark microbial CO2 fixation substantially contributes to the C balance of soils and what factors control this process. Therefore, the objective of this study was to quantitate dark microbial CO2 fixation in temperate forest soils, to determine the relationship between the soil CO2 concentration and dark microbial CO2 fixation, and to estimate the relative contribution of different microbial groups to dark CO2 fixation. For this purpose, we conducted a 13 C-CO2 labeling experiment. We found that the rates of dark microbial CO2 fixation were positively correlated with the CO2 concentration in all soils. Dark microbial CO2 fixation amounted to up to 320µgCkg-1 soilday-1 in the Ah horizon. The fixation rates were 2.8-8.9 times higher in the Ah horizon than in the Bw1 horizon. Although the rates of dark microbial fixation were small compared to the respiration rate (1.2%-3.9% of the respiration rate), our findings suggest that organic matter formed by microorganisms from CO2 contributes to the soil organic matter pool, especially given that microbial detritus is more stable in soil than plant detritus. Phospholipid fatty acid analyses indicated that CO2 was mostly fixed by gram-positive bacteria, and not by fungi. In conclusion, our study shows that the dark microbial CO2 fixation rate in temperate forest soils increases in periods of high CO2 concentrations, that dark microbial CO2 fixation is mostly accomplished by gram-positive bacteria, and that dark microbial CO2 fixation contributes to the formation of soil organic matter.

Arctic soil carbon turnover controlled by experimental snow addition, summer warming and shrub removal

Northern latitude tundra heaths have accumulated large amounts of organic carbon (C) in the soil. Changes in climatic conditions such as temperature and winter precipitation might affect the C balance and potentially change these tundra ecosystems from being C sinks to sources of CO2 emitted to the atmosphere. However, studies on C fluxes with single and combined winter snow and summer warming effects are scarce. This study investigates gross ecosystem production (GEP), ecosystem respiration (ER), net ecosystem production (NEP) and carbon isotopic composition of CO2 emitted from a dry heath in arctic Greenland one and two years following field manipulations of summer temperature, shrub abundance and winter snow depth. Our aims were to quantify climatic change effects on CO2 fluxes and the growing season carbon balance of the ecosystem and to investigate shifts in δ13C of emitted CO2 potentially due changes in emission from old soil C versus recently fixed carbon. Ecosystem CO2 fluxes and δ13C-CO2 were measured using closed chambers, and soil CO2 concentrations and δ13C were measured depth-specifically using gas probes.We found a significant increase of CO2 emissions in all treatments during both years. Growing season NEP increased by 38 and 73% with 1 m enhanced winter snow depth, by 113 and 144% with summer warming and by 61 and 320% with total shrub removal in 2013 and 2014, respectively. The snow effect can be explained by the delay in the onset of growth as indicated by early season reduced vegetation greenness. The effect of warming was a result of an increase of ER by 39 and 32%, and the effect of shrub removal was mainly due to a reduction in GEP by 34 and 48%, in 2013 and 2014, respectively. Furthermore, the δ13C of the carbon source of CO2 emitted from warmed plots increased significantly two years after the experiment was initiated. This might indicate increased decomposition of 13C enriched soil organic matter and hence increased mineralization of the old carbon stock in the soil under warmed conditions. The increase of NEP, the additive response of all treatments, and the indications of increased emission of carbon from old stocks due to warming (or warming-induced drying), demonstrate the risk of a relatively fast feedback to climate warming during the snow-free season.

Variations of soil CO2 concentration and pCO2 in a cave stream on different time scales in subtropical climatic regime

In karst regions, soil CO2 is a major chemical driving force for the karst processes and finally has a significant impact on the hydrochemical processes of karst underground river. Hydrochemical features, soil and climatic parameters with a high-temporal resolution have been monitored on different scales (daily scale, seasonal scale and interannual scale, storm scale) in the Xueyu Cave watershed from 2009 to 2015. The aim of this study is to understand how cave stream pCO2 and hydrochemistry respond to overlying soil carbon recharge on different time scales. The results show that the variational amplitudes of the hydrochemistry in Xueyu Cave underground river (XUR) tend to be in the order: storm-scale > seasonal > interannual > daily scale. Soil CO2, pCO2 (CO2 partial pressure in the XUR) and Spc (specific conductivity) were higher in summer and autumn than those in winter and spring. The synchronous variations of XUR pCO2 with soil CO2 concentrations in the same order of magnitude confirm the “soil CO2 effects” on the formation of XUR hydrochemical features. The storm-scale fluctuations of hydrochemistry in XUR water are especially depending on the intensities of rainfalls that determine whether the “dilution effects” or the “CO2 effects” are predominant in the stream during rainfall events. At the same time, soil moisture and soil CO2 work as important factors for controlling pCO2 variations in the XUR. The identified relationship of soil-XUR pCO2 suggests a temperature control on carbonate weathering on daily and seasonal scale but a rainfall/soil moisture control on storm and annual scale. The combined effect of point and diffused infiltration that delays the arrival of storm flows determines the fluctuations of the discharge and pCO2 variation. Defining relationships between CO2 from overlying soils and groundwater offers the chance to explore the processes at different time scales, potentially increasing our ability to understanding the carbon dynamics in karst systems.

Straw-derived biochar mitigates CO2 emission through changes in soil pore structure in a wheat-rice rotation system.

To better understand the relationships between soil pore structure features and soil CO2 emission and soil organic carbon (SOC) sequestration following different straw return modes, undisturbed soil cores (0-5 cm and 5-10 cm) were collected from a rice-wheat rotation system under 4 straw return treatments as (1) no straw return (CK), (2) straw direct return (DR), (3) straw biochar return (BR); (4) straw-pig manure fermentation return (FR) for six years. Pore structure parameters including pore size distribution, porosity, connectivity, anisotropy and fractal dimension (FD) were determined using X-ray computer tomography. Soil CO2 flux and concentrations of SOC, readily oxidable carbon and nutrients were also measured. The results showed that BR and FR had significantly higher SOC concentration than DR and CK. Porosity and number of >500 μm and 500-100 μm macropores, FD and connectivity were significantly highest under FR and was lowest under BR. FR and DR produced 28.1%-32.4% higher C-CO2 than CK and BR in wheat growing season, and 9.80%-16.9% higher in rice season. Soil CO2 emission and C concentrations were significantly related to soil pore structure parameters. The CO2 emission was most significantly related to number of >500 μm pores and FD, indicating that poorly developed pore structure under BR hindered the production and diffusion of CO2 from soil. These results enhanced our understanding of the relationship between soil pore structure and CO2 emission following biochar application, and provided evidence for decision making process in choosing proper straw managements to promote SOC sequestration and reduce CO2 emission.

The electrical properties characterization of MG-811 gas sensor toward the temperature alteration of soil testing chamber

The concentration of CO2 in soil and air is strongly influenced by temperature. When the temperature increase, the thermal energy will increase too and make the particle motion faster. In detecting CO2 gases, the MG-811 gas sensor has a high sensitivity in detecting CO2 gases in the air. The purpose of the research is characterized the electrical properties of MG-811 gas sensor toward temperature alteration. The used method is the experimental method, where the chamber is made of iron filled with CO2 derived from the CO2 gas tube. In the chamber has been paired digital thermometer and MG-811 gas sensor. The temperature alteration in the CO2 gas is regulated by the heater element attached to the chamber. The output of the MG-811 gas sensor will be processed by microcontroller, so it measures the CO2 concentration in units of parts per millions (ppm). The higher the measured temperature on the gas causes faster particle motion, the measured CO2 gas concentration is high and the resulting output voltage is low. But it happens if the temperature changes high, because the gas sensor response is slower than the temperature sensor used.

Characteristics of soil profile CO<sub>2</sub> concentrations in karst areas and their significance for global carbon cycles and climate change

Abstract. CO2 concentrations of 21 soil profiles were measured in Zhaotong City, Yunnan Province. The varying characteristics of soil profile CO2 concentrations are distinguishable between carbonate and noncarbonate areas. In noncarbonate areas, soil profile CO2 concentrations increase and show significant positive correlations with soil depth. In carbonate areas, however, deep-soil CO2 concentrations decrease and have no significant correlations with soil depth. Soil organic carbon is negatively correlated with soil CO2 concentrations in noncarbonate areas. In carbonate areas, such relationships are not clear. This means that the special geological process in carbonate areas – carbonate corrosion – absorbs part of the deep-soil-profile CO2. Isotope and soil pH data also support such a process. A mathematical model simulating soil profile CO2 concentration was proposed. In noncarbonate areas, the measured and the simulated values are almost equal, while the measured CO2 concentrations of deep soils are less than the simulated in carbonate areas. Such results also indicate the occurrence of carbonate corrosion and the consuming of deep-soil CO2 in carbonate areas. The decreased CO2 concentration was roughly evaluated based on stratigraphic unit and farming activities. Soil pH and the purity of CaCO3 in carbonate bedrock deeply affect the corrosion. The corrosion in carbonate areas decreases deep-soil CO2 greatly (accounting for 5.2 %–66.3 % with average of 36 %) and naturally affects the soil CO2 released into the atmosphere. Knowledge of this process is important for karst carbon cycles and global climate changes and it may be a part of the “missing carbon sink”.

Whole-plant instantaneous and short-term water-use efficiency in response to soil water content and CO2 concentration

Water-use efficiency (WUE) is a key parameter to understand plant survival strategies and promote forest management in response to climate change. Here, the whole-plant instantaneous WUE (WUEi-P) and short-term WUE (WUEs-P) were investigated in response to soil water content (SWC) and atmosphere CO2 concentration (Ca). The WUEi-P was measured using a plant chamber and mini-lysimeters. The WUEs-P was estimated using different isotopic models. These estimates were compared with measured results (WUEs-P,mea; the ratio of the whole-plant cumulative CO2 assimilation to water loss). Except at severe drought, WUEi-P generally decreased with increasing SWC, but increased with increasing Ca. At mild and moderate drought, the percentage increases in WUEi-P by elevating Ca from 600 to 800 μmol·mol−1 (23.45%–32.78%) were higher than those from 400 to 600 μmol·mol−1 (9.12%–8.33%). However, the opposite pattern was found under well- and excessive-watered conditions. The variation in WUEs-P,mea in response to Ca × SWC was similar to that in WUEi-P. The developed whole-plant isotopic model (i.e. the plant classical model) is based on the hypothesis that the mesophyll conductance (gm) should be considered to model whole-plant WUE. This model provided the best fit with WUEs-P,mea compared with previously proposed models (plant linear model, as well as leaf linear and classical model). This indicated that the contribution of gm, whole-plant respiration, and unproductive water loss should be considered when scaling from leaf to whole-plant level. These results have implications for mechanisms of plant water and carbon cycles and improve predictive capability for whole-plant WUE from δ13C.

CO2 leakage detection in the near-surface above natural CO2-rich water aquifer using soil gas monitoring

Conventional soil gas monitoring methods were applied above a natural low-level CO2 reservoir to locate natural CO2 leakage and assess effectiveness in monitoring geological carbon storage sites. The concentrations of the soil gas (N2, O2, and CO2) and carbon-13 isotopes of soil CO2 (δ13CCO2) were determined for ninety-four soil gas samples that were collected at a depth of ∼60 cm. The CO2 flux was also measured at the same sampling locations. The 93 soil gas samples were divided into two groups: Group A with low soil CO2 concentrations and high δ13CCO2, which was influenced by the atmospheric air, and Group B with high soil CO2 concentrations and low δ13CCO2, which originated from microbial processes. Sample M17, which was close to a CO2-rich water well, had an exceptionally high soil CO2 (36.0% v/v), δ13CCO2 (-5.7‰), and flux (546.2 g/m2/d), indicating geogenic CO2 inflow to the soil layer and discharge through the surface. This study shows that conventional soil gas monitoring methods are useful for locating CO2 leakage. A dense grid soil CO2 sampling near wells and periodic investigations are crucial for further understanding of the CO2 flow paths in the soil layer.

Changes in soil N2O and CH4 emissions and related microbial functional groups in an artificial CO2 gassing experiment

Potential CO2 leakage is a major concern for carbon capture and storage (CCS). The effects of high soil CO2 concentration on microbes is a major element of impact assessments of CO2 leakage on terrestrial ecosystems. We conducted a field experiment to investigate the responses of microbial functional groups of ammonia-oxidizers, methanogens, and methanotrophs in high soil CO2 conditions. A single-point injection gassing plot (2.5 m × 2.5 m in size), which had 52.2% CO2 in the center (radius = 0.5 m) and 5.5% in the edge (radius = 1.7 m) at 10 cm depth, was employed. N2O and CH4 emissions increased after 1 day of injection because injected CO2 was instantly utilized by nitrifiers and methanogens. This suggests that the activities of the selected microbes could be stimulated by high soil CO2 concentrations. Prolonged CO2 injection has toxic effects on aerobic nitrifiers, but may favor anaerobic methanogens. However, the early stimulatory effects of high soil CO2 on N2O and CH4 production did not last to the end of injection. These results imply that increased N2O and CH4 emissions could be the minor side effects of high soil CO2. Microbes responded faster than plants to high soil CO2, with responses observed as late as 7 days after injection. The inhibition of plant absorption of soil water and nutrients by high soil CO2 concentrations may also influence microbial responses. Moreover, high soil water content could retard underground CO2 diffusion, which would magnify CO2 impacts on plants and microbes. Our results suggest that microbial response could be used as an early indicator of the impact assessments of CO2 leakage on soil ecosystems. An understanding of the interaction among soils, plants, and microbes would be helpful in assessing the biological risks of potential CO2 leakage.

Geochemical signals related to the 2011–2012 El Hierro submarine eruption

On 10 October 2011, a submarine volcanic eruption began 2 km south of the island of El Hierro (Canary Islands, Spain). It was the first eruption after 40 years of quiescence in the Canarian archipelago. Since mid-July 2011, a multiparametric network has been deployed by the Instituto Geográfico Nacional (hereinafter IGN) to monitor volcanic processes. The data recorded by five stations, measuring the air and soil temperature, CO2 and radon concentration in the air inside four galleries and one well, are the focus of the present paper. Two important anomalies were found that improve comprehension of the volcanic process. First, a clear increase in CO2 concentration in one gallery (from 825 ± 19 to 2305 ± 35 ppm) which seems to be mainly controlled by ground deformation measured during the unrest period preceding the eruption. Second, a relationship between radon concentration in air in a well located in the northern side of the island with seismic energy release (several peaks with up to 115% increase), and ground deformation (50% growth in background level), also before the eruption onset. Lastly, changes in radon concentration during eruptive period seem to be modulated by seismic activity (increases up to 233%), which in turn is likely related to variations in magma rheology.

Soil gas monitoring at the Illinois Basin – Decatur Project carbon sequestration site

An extensive monitoring, verification, and accounting (MVA) program was carried out from 2011 to 2016 as part of the Illinois Basin – Decatur Project (IBDP), a large-scale carbon capture and storage (CCS) demonstration project in Decatur, Illinois, USA. As part of the monitoring program, a near-surface monitoring network for soil gas was used to characterize the natural variability of CO2 and identify anomalies that could be associated with CO2 leakage in the vadose zone. In the fall of 2011, 21 permanent soil gas sampling nests were installed on-site and three nests were installed off-site as reference locations. Soil gas was collected from three depth intervals (15–30, 47–61, 107–122 cm) at each nest. Fixed gas (CO2, N2, O2, and light hydrocarbon) concentrations, stable carbon isotopic composition (δ13C), and radiocarbon (14C) content of CO2 in soil gas were monitored during the pre-injection, injection, and post-injection phases from 2011 to 2016. Both CO2 concentrations and carbon isotopic compositions showed large spatial and temporal variations; however, the relationships among CO2, N2, and O2 concentrations in soil gas indicated that these variations should be attributed to natural processes and not CO2 leakage. Soil CO2 concentrations responded to temperature and precipitation variations and increased with increasing soil depth. While 14C cannot be used to determine the occurrence of CO2 leakage at IBDP site due to the indistinctive signature between injected CO2 and soil gas CO2, experiences at IBDP validated that δ13C can serve as an effective natural tracer at this site. Results from this project have value for future industrial CCS projects that plan to use soil gas monitoring techniques for site characterization and leakage detection.

Difference in the relationship between soil CO2 concentration and the karst-related carbon cycle under different land use types in southwest China

As an important driving force for karstification, soil CO2 has a close relation with karst-related carbon cycle. However, their relationship may be disturbed when H2SO4 and HNO3 participate in karstification. Here, soil CO2 and spring water samples were collected from two catchments to examine the dynamics of carbon under different land use types. The net CO2 consumption at the Baishuwan spring catchment (BSW; range 1.7–2.69 mmol/L, average of 2.21 mmol/L) was higher than it was at the Hougou spring catchment (HG; range − 0.63 to 0.02 mmol/L, average of − 0.24 mmol/L). Due to the participation of H2SO4 and HNO3, CO2 was released from bedrock and reduced net CO2 consumption when this portion of CO2 escaped from the water. With regard to soil CO2 concentration, a bidirectional gradient of CO2 concentration occurred at BSW, while alternating bidirectional and unidirectional gradients occurred at HG. However, the δ13C of soil CO2 could not confirm whether the vertical changes in soil CO2 concentration as well as net CO2 consumption were related to the CO2 released from bedrock to soil. With regard to seasonal changes, net CO2 consumption was consistent with soil CO2 concentration at BSW, while the reverse relationship was found at HG. These observations indicated that soil CO2 concentration was not the dominant factor controlling net CO2 consumption at HG, which was affected by H2SO4 and HNO3, and more CO2 escaped from the water due to the reduced water–rock reaction time in the rainy season.

Soil Priming Effect Mediated by Nitrogen Fertilization Gradients in a Semi-arid Grassland, China

The priming effect is well acknowledged in soil systems but the effect of nitrogen (N) fertilization remains elusive. To explore how N modifies the priming effect in soil organic matter (SOM), one in situ experiment with 13C labeled glucose addition (0.4 mg C g-1 soil, 3.4 atom % 13C) was conducted on soil plots fertilized with three gradients of urea (0, 4 and 16 g N m-2 yr-1). After glucose addition, the soil CO2 concentration and phospholipid fatty acid (PLFA) were measured on day 3, 7, 21 and 35. The study found that N fertilization decreased soil CO2, PLFA and the fungi to bacteria ratio. Glucose triggered the strongest positive priming in soil at 0 g N m-2 yr-2, meanwhile N fertilization decreased SOM-derived CO2. Soil at 4 g N m-2 yr-2 released the largest amount of glucose-derived carbon (C), likely due to favorable nutrient stoichiometry between C and N. Stable microbial community biomass and composition during early sampling suggests “apparent priming” in this grassland. This study concludes that N fertilization inhibited soil priming in semi-arid grassland, and shifted microbial utilization of C substrate from SOM to added labile C. Diverse microbial functions might be playing a crucial role in soil priming and requires attention in future N fertilization studies.

Diurnal and seasonal patterns of soil CO2 efflux from the Pichavaram mangroves, India.

The diurnal and seasonal variation of soil carbon dioxide (CO2) flux was measured in the Pichavaram mangrove forest, the Southeast coast of India from February 2016 to October 2016 using an automated soil CO2 flux chamber system. Maximum soil CO2 efflux reached at 14:00h and minimum at 00:00h. The surface soil CO2 concentration ranged from 375 to 532ppm with the mean 405 ± 18ppm. The daily soil CO2 flux varied from near zero to about 7μmolm-2s-1 with a mean value of 2.4 ± 1.3μmolm-2s-1. The highest seasonal CO2 efflux from soil was during the summer and premonsoon seasons, whereas low flux values were recorded during the monsoon season. Soil CO2 efflux values were highly correlated with soil temperature. Tidal inundation during monsoon season, extreme drought condition in summer, and unusual precipitation are the major factors controlling the soil CO2 flux.

Spatial and Temporal Analysis of Temperature and Gaseous Emission Inside a Gallery in An Active Volcanic Island (Tenerife, Canary Islands)

In Tenerife there are a vast number of sub-horizontal blind water mines, called “galleries”. Seven air and soil temperatures and CO2 concentration profiles in air were carried out inside the Rio de Guia gallery (hereinafter RdG). An anomalous stable maximum temperature point (hereinafter MTP) was found around 2000 m from the entrance. During the warm period, a clear CO2 stagnation was detected before MTP, showing concentrations up to 14,000 ppm. In order to study gas emission and its dynamics inside the gallery, four stations were deployed around MTP. All stations recorded air and soil temperatures, and CO2 and Rn concentration in air from November 2009 to January 2011. After analyzing this dataset, it was possible to characterize the influence of MTP. This thermal anomaly divided the gallery into two sections. In the cold period, the outer section located outwards from MTP became colder while the inner section warmed up owing to a less heat transfer into the deepest part of the gallery. There were several short periods when variations in barometric pressure created an advection movement that was able to temporally change the gas behavior inside the gallery. Two soil gas samples were taken around MTP and their δ13C (CO2) ratios suggested a magmatic origin. All data were combined to create a model for the gas and thermal dynamics inside the gallery. This model, together with identification of background levels in each parameter, allows to identify any anomalous signal that could be elated with changes in volcanic activity.