Soil-respired CO2 Research Articles

Tillage systems influence on greenhouse gas emission factor and global warming potential under rice-mustard-rice cropping system

ABSTRACT Conventional tillage (CT) degrades soil and environmental quality in many major cropping systems. Conservation agriculture, like reduced tillage, can play an important role in maintaining soil organic carbon (SOC) storage and in minimizing greenhouse gas (GHG) emissions from crop fields. An experiment was conducted at the Bangladesh Agricultural Research Institute (BARI), Gazipur to evaluate GHG emission, global warming potential (GWP), GHG intensity and net SOC variations in rice-mustard-rice cropping systems under CT and strip tillage (ST). The emissions of nitrous oxide (N2O) and carbon dioxide (CO2) varied significantly because of CT and ST tillage practices. The ST reduced 24–47% methane (CH4) emission factor, 20–32% CH4 flux, 32–46% GHG intensity and 31–47% GWP than CT practice. In mustard crop, ST reduced 55–61% of GHG intensity and 52–58% of GWP compared to CT. There was about 33% increase in N2O emission and 24% augmentation of soil respiratory CO2 with ST compared to CT. About 8% absorption of net ecosystem CO2, 9–11% of net SOC and 10% of rice equivalent yields increased in ST compared to CT. It is concluded that ST can minimize soil C loss, improve net ecosystem CO2 absorption, and reduce GHG intensity, GWP under rice-mustard-rice systems in Asian countries.

Aggregational Differentiation of Soil-Respired Co2 and its Δ13c Vary Across Land-Use Types

Aggregational Differentiation of Soil-Respired Co2 and its Δ13c Vary Across Land-Use Types

The proximity of a highway increases CO2 respiration in forest soil and decreases the stability of soil organic matter

Roadways traverse many forest areas and they often have harmful effects on forest soils, including the modified stability of soil organic matter (SOM). Soil CO2 respiration is an important indicator of SOM biological stability. The aim of this study was to test the hypotheses that a roadway will (1) modify the composition of the cation exchange capacity of adjacent forest soils, and (2) significantly decrease the stability of SOM. Two study sites were established in Scots pine and Silver fir stands, located close to the S7 highway in central Poland, which was opened to traffic in 1984. From each site, samples were taken at 2, 12 and 22 m from the forest edge. Soil CO2 respiration was determined using closed chamber incubation with an alkali trap. We also conducted a comprehensive analysis of soil chemical properties. The stoichiometric ratios of chosen chemical parameters to total carbon (Ct) were calculated. In both sites, we observed increased soil pH and CO2 respiration in the vicinity of the highway, as well as increased ratios of exchangeable calcium (Ca), magnesium (Mg) and sodium (Na) to Ct. In the fir site, the humic and fulvic acids, the dissolved organic carbon (DOC) content and aluminum (Al) to Ct ratio were depleted in close proximity to the highway. We suggest that the combined effect of Ca and Na ions, originating from winter de-icing, caused the depletion of Al and hydrogen (H) in the soil close to the forest edge and, therefore, resulted in lower SOM stability expressed as the decreased DOC and pyrophosphate-extractable carbon content, as well as the release of CO2. We conclude that the changes of SOM stability with distance were the effect of modification of ion-exchange relationships (particularly base cations versus Al3+ with H+) rather than forest stand species or intrinsic SOM properties (like functional groups, the recalcitrance of bindings etc.). Our work supports earlier studies, confirming the significant impact of Al and H on SOM stability.

Atmospheric CO2 estimates based on Gondwanan (Indian) pedogenic carbonates reveal positive linkage with Mesozoic temperature variations

CO 2 is an important greenhouse gas that is known to drive global climatic changes. Multiple studies tracking p CO 2 changes throughout the Phanerozoic have highlighted the linkage between CO 2 levels and the corresponding icehouse-greenhouse conditions. However, deviations from the above relationship due to inconsistencies in p CO 2 estimation, as well as large time-steps in existing geochemical models and gaps in proxy data suggest that the paleo- p CO 2 record is not always well-constrained. Here, we attempt to reconstruct atmospheric CO 2 concentration for parts of the late Early and Middle Triassic and Early Cretaceous from several carbonate-forming paleosols of the Indian Gondwana. We measured the carbon isotopic composition of pedogenic carbonates (δ 13 C carb ) and organic matter occluded within soil carbonates (δ 13 C org ) from Pachmarhi, Denwa, and Bagra Formation of the Satpura Basin ( n = 60) to estimate CO 2 using a pedogenic carbonate-based paleo-barometer. The late Early Triassic (Olenekian) shows low CO 2 concentrations (562 ± 426 ppmV), which is followed by an increase (822 ± 523 ppmV) in the Middle Triassic (Anisian). The Early Cretaceous is found to have the highest average concentration (1517 ± 594 ppmV). Our p CO 2 estimates are well correlated with the existing proxy record and geochemical models and suggest fluctuations in CO 2 levels that are consistent with temperature variations previously estimated for the periods. • Atmospheric CO 2 is reconstructed from Gondwana paleosols for parts of the Mesozoic. • Our pCO 2 data correlate well with geochemical models and other proxies. • Atmospheric CO 2 estimates also show excellent correlation with temperature. • Early parts of Triassic show large variations in atmospheric CO 2 concentration. • A new dynamic soil-respired CO 2 -proxy is formulated from modern soil data.

External controls on CO2 in Gibraltar cave air and ground air: Implications for interpretation of δ13C in speleothems

The principles of cave ventilation and ground air advection are outlined. CO2 concentrations were monitored every 2–4 h from 2006 to 2012 at twelve locations in two Gibraltar caves, New St. Michael's (240–275 m altitude) and Ragged Staff (0–70 m), providing detailed records of spatial distribution and temporal changes responding to transient meteorological conditions and seasonal cycles. Cave atmospheres are dynamic mixtures of external air and CO2-rich ground air containing soil-respired CO2 augmented by CO2 derived from oxidation of organic matter washed down into the vadose fracture porosity. The dominant feature of the cave air records is seasonal alternation between high and low CO2 states caused by reversals in ventilation and ground air advection into or away from the caves. The high and low pCO2 states are tightly coupled between the two caves in an antiphase relationship, with rapid switching in response to temperature-controlled density differences between external air and isothermal ground air at mean annual surface temperature (18 °C). The diurnal temperature cycle modulates this pattern, producing four ventilation-advection modes. Summer and winter modes occur when diurnal temperatures are respectively entirely above or below the core temperature of the Rock. During transitional modes the core temperature lies within the diurnal range and pCO2 fluctuates rapidly as the flow of low-CO2 external air through cave entrances alters in response. Strong easterly winds reduce CO2 concentrations in ground air entering the caves and progressively lower cave air CO2. The effects of the CO2 regime on δ13C in speleothem are restricted to variations of 2–3‰, suggesting that larger changes of up to 6‰ across major climatic transitions probably reflect changes in production, transport and oxidation rate of organic matter in the vadose zone. Direct observations of these processes would improve future understanding of the climatic significance of δ13C records in speleothems.

Evaluation of the CALPUFF model performance for the estimation of the urban ecosystem CO2 flux

Land-use and land-cover changes due to urban expansion is recognized as one of the crucial factors affecting carbon dioxide emissions. In this study, the land conversion effects on soil CO2 fluxes associated with temperate re-established grasslands within the Forest Botanical Garden found on an anthropogenic landform were investigated. The present work analyses the capabilities and requirements of the CALPUFF Lagrangian puff air quality modelling system to simulate the spatial distribution of ecosystem respired CO2 in the urban domain. The results are validated against the available observations of CO2 fluxes in the urban environment using the closed-chamber method with the measurements of the stable carbon isotope ratio (δ13C) of daytime soil-respired CO2. The isotope mass balance partitioning approach was applied to distinguish biogenic portions of CO2 from the admixture of atmospheric air.The spatial and temporal amplitude of the simulated CO2 concentrations from the CALPUFF model showed considerable agreement with the tracer measurements of the biogenic CO2 component in the near-ground air (0.25 m). In most cases, however, the CALPUFF predictions of ecosystem-derived CO2 showed a general tendency toward considerable underestimation of real concentration levels. Such discrepancies are related to the difficulties associated with the optimization of biospheric CO2 flux and uptake from ecosystems by means of local-scale modelling. The modelled results implied that the CALPUFF performance in the dispersion simulation of CO2 concentrations within the urban ecosystems is very sensitive to the initial meteorological conditions, grid resolution, measurement timescale, and the calculated gas flux rate from soils. A significant negative correlation was found between hourly values of the average modelled CO2 and observed wind speed during the entire study campaign (r = −0.58 and ρ = −0.82 for Pearson and Spearman statistics, respectively, p < 0.05). Moreover, analysis of the impact of the deposition parameters on changes in the atmospheric concentration of carbon dioxide indicated significant dependency of the temporal CO2 distribution patterns on the precipitation-based events. According to the obtained estimates, the wet deposition rate during rain events was approximately two orders higher than the average dry deposition flux.Overall, the present case study indicates that the CALPUFF model has a rather acceptable predictive ability. A better agreement of model predictions and all field measurements, however, require further studies of CO2 exchange between the ecosystem and atmosphere and understanding where they need to be improved.

Quantifying soil-respired CO2 on the Chinese Loess Plateau

Soil respiration is one of the dominant fluxes of CO2 from terrestrial ecosystems to the atmosphere. Accurate quantification of soil respiration is essential for robust projection of future climate variation and for reliable estimation of paleoatmospheric CO2 levels using soil carbonates. Soil-respired CO2, which is the most uncertain factor in estimating atmospheric CO2 concentration, has been calculated from modern observations of surface soils and from proxy indicators of paleosols formed during time periods of known atmospheric CO2. However, these estimations provide a wide range of S(z) values from past to present. To directly compare modern observation with past estimation, here we first monitored soil CO2 profiles in a Holocene profile on the western Chinese Loess Plateau (CLP) for two years, providing direct measurements of soil-respired CO2 at the depth where carbonate nodules likely formed. We then collected carbonate nodules below last interglacial paleosol (S1) from two N-S-aligned transects across the CLP to back-calculate soil-respired CO2. The mean back-calculated S(z) from S1 carbonate nodules vary from 539 ± 87 ppm to 848 ± 170 ppm in the sections on the northwestern and southeastern CLP, respectively. The mean value of directly measured soil-respired CO2 on the western CLP is 572 ± 273 ppm before the onset of summer monsoon, consistent with the back-calculated S(z) in northwestern sections. Our results suggest that spatial S(z) variations are mainly controlled by monsoonal precipitation during the summer season on the CLP. To better constrain the high end of S(z), more monitoring work is needed in higher precipitation areas on the southeastern CLP.

Planosol CO2 Respiration, Chemical and Physical Properties of Differently Tilled Faba Bean Cultivation

Soil tillage intensity influences the chemical composition of soil, the distribution of nutrients, and soil physical and mechanical properties, as well as gas flows. The impact of reduced tillage on these indices in faba bean cultivation is still insufficient and requires more analysis on a global scale. This study was carried out at Vytautas Magnus University, Agriculture Academy (Lithuania) in 2016–2018. The aim of the investigation was to establish the influence of the tillage systems on the soil chemical composition, temperature, moisture content, and CO2 respiration in faba bean cultivation limited by the semi-humid subarctic climate. On the basis of a long-term tillage experiment, five tillage systems were tested: deep and shallow moldboard plowing, deep cultivation-chiseling, shallow cultivation-disking, and no-tillage. Results showed that in conditions of plowless tillage systems, the content of precrops’ residues on the topsoil before the spring tillage was 5 to 15 times higher than in plowed plots. It undoubtedly was for the amount of available nutrients in the soil, soil temperature, and moisture content. Plowless and no-tillage systems could initiate an increase in the amount of available nutrients in soil. The highest concentration of chemical elements was found in no-tilled plots. So faba bean crops could largely increase the composition of potassium and total nitrogen and stabilized CO2 respiration from soil during one vegetative period.

Coupled carbon and oxygen isotope model for pedogenic carbonates

Carbon and oxygen isotope values of ancient pedogenic carbonates reflect the paleoenvironmental conditions under which the carbonates formed. Carbon isotope values are commonly used to reconstruct pCO2, C3 vs. C4 plant types, and carbon cycle dynamics. Oxygen isotope values of the same carbonates have been used to reconstruct past temperatures and elevations. In the geologic record, changes in these isotope values can be difficult to interpret because they are affected by a suite of multiple local (e.g. precipitation and temperature) and global variables (e.g. pCO2 and global temperature) that can be difficult to separate. In this study, we develop a semi-mechanistic model of factors that affect carbon and oxygen isotope values of pedogenic carbonate. The model links these factors to a common suite of environmental variables using theoretical and empirical relationships. We test and optimize the model using modern environmental data and a compilation of modern pedogenic carbonate isotope measurements. This comparison indicates that the model best reproduces the observed data when carbonates are assumed to form under conditions where (1) evaporation affects oxygen isotope values of source waters at shallow soil depths only, (2) source waters mix precipitation from prior to and during the period of carbonate formation, and (3) soil CO2 respiration rates are anomalously low. Global predictions from the optimized model suggest strong spatial variation in both carbon and oxygen isotope values of pedogenic carbonate and highlight areas where future measurements from modern samples might provide strong tests of the model. The model also demonstrates coherent patterns of coupled δ13Ccarbonate and δ18Ocarbonate value variation associated with different types of environmental forcing, and offers a new framework for interpreting paired carbon and oxygen isotope data from ancient pedogenic carbonates to constrain paleoenvironmental change.

Estimation of annual CO2 efflux of moss biocrust through measuring and simulating its respiration rate in a semiarid climate

Biocrust is a potentially extensive living cover in drylands, which comprises much of the land surface, but presently its contribution to the soil respiration rate (Rs) and CO2 efflux is still not clearly understood. In this study, we continuously measured the Rs of moss-dominated biocrust (biocrust and biocrust covered soil) and bare soil, together with soil temperature and moisture, for ~100 days each in a semiarid climate on the Chinese Loess Plateau. We modeled Rs across a two-year period, based on its relationship with soil temperature and moisture. Using the model, the seasonal variation of the Rs was simulated for biocrust and bare soil, and their annual CO2 efflux were further estimated. We also obtained samples of the biocrust layer and bare soil surface and analyzed their physicochemical properties and enzyme activities to explain the biocrust effects on Rs. Our results showed that the measured Rs of the biocrust and bare soil ranged from 0.05 to 7.62 and 0.02–2.73 μmol m−2 s−1, respectively, and was closely exponentially related to the dynamics of soil temperature and moisture (in threshold relationships). The variations of Rs in both the biocrust and bare soil were strongly predicted in a regression model by R2 ≥ 0.50 and P < 0.001. Through this model, we simulated the seasonal variations of Rs, which averaged 1.03 ± 0.01 and 0.54 ± 0.01 μmol m−2 s−1 (F = 225.51, P < 0.001) across all seasons for the biocrust and bare soil, respectively. We further estimated that the annual CO2-C efflux through respiration of the biocrust was 390 g m−2 yr−1 and that of the bare soil was 203 g m−2 yr−1, indicating that the presence of the biocrust layer annually contributed 91.8% (187 g m−2 yr−1) more soil respiration in comparison to the bare soil. Moreover, the main correlates with Rs shifted from largely abiotic, e.g. soil texture and total phosphorus content, in bare soils to biotic, e.g. indicators of carbon and nitrogen content, in biocrust soils. This finding implies that the contribution of the biocrust to Rs is linked to the carbon fixed and organic nutrients stored in the biocrust layer. In conclusion, moss-dominated biocrust highly accelerates soil respiration and increases gross soil CO2 efflux, possibly through regulating soil temperature and moisture, improving soil physicochemical properties, increasing soil enzyme activities, and accelerating decomposition of biocrust-fixed and -stored carbon.

The “breathing spots” in karst areas—the sites of advective exchange of gases between soils and adjacent underground cavities

Microclimatic processes were studied in the soil of the well-defined “breathing spot” named Půlhodina (BSP) in the Hranice Karst (Czech Republic). The results have indicated that air is exchanged between the external atmosphere and a supposed underground cavity under air-buoyancy control. Upward airflow ventilation mode (UAF mode) and downward airflow ventilation mode (DAF mode) were distinguished. The virtual temperature of switching between both modes was about 16.5 °C. At the UAF mode, the underground air is rising from the cavity through the BSP, warms soil, and carries out the underground CO2. At the DAF mode, the external air is sucked into the cavity through the BSP soil, promoting the advective flux of the soil-respired CO2 deeper into the cavity. Whereas the warming of the soil is a dominant process in the UAF mode, the CO2 advective flux into the cavity is the main process in the DAF mode. The simplified mathematical model was derived as a function of the external air temperature and the soil air temperature to simulate the time evolution of CO2 concentration in the BSP. Despite simplifying assumptions, this model showed a good agreement with the collected data. The advective CO2 flux from a breathing spot soil may significantly contribute to the total CO2 flux into the adjacent underground cavity. Its total values may reach 4 × 10−3 mol s−1 or even more, based on the actual CO2 concentration, the exchanged airflow magnitude (both controlled by external temperature), and the breathing spot area. This conclusion is important for karsologists studying the cave CO2 budget, CO2 sources, and the mechanisms of CO2 transport into caves.

Aridity-driven decoupling of δ13C between pedogenic carbonate and soil organic matter

Abstract Pedogenic carbonate is an invaluable archive for reconstructing continental paleoclimate and paleoecology. The δ13C of pedogenic carbonate (δ13Cc) has been widely used to document the rise and expansion of C4 plants over the Cenozoic. This application requires a fundamental presumption that in soil pores, soil-respired CO2 dominates over atmospheric CO2 during the formation of pedogenic carbonates. However, the decoupling between δ13Cc and δ13C of soil organic matter (δ13CSOM) have been observed, particularly in arid regions, suggesting that this presumption is not always valid. To evaluate the influence of atmospheric CO2 on soil δ13Cc, here we performed systematic δ13C analyses of paleosols across the Chinese Loess Plateau, with the sample ages spanning three intervals: the Holocene, the Late Pleistocene, and the mid-Pliocene warm period. Our paired δ13Cc and δ13CSOM data reveal broadly divergent trending patterns. Using a two-component CO2-mixing model, we show substantial incorporations of atmospheric CO2 (up to 60%) into soil pore space during carbonate precipitation. This result readily explains the enrichment of δ13Cc and its divergence from δ13CSOM. As a consequence, δ13C of pedogenic carbonates formed under semiarid and/or arid conditions are largely driven by regional aridity through its control on soil CO2 composition, and thus cannot be used to evaluate the relative abundance of C3 versus C4 plants. Nonetheless, these carbonates can be applied for atmospheric CO2 reconstructions, even for periods with low CO2 levels.

Drought and recovery effects on belowground respiration dynamics and the partitioning of recent carbon in managed and abandoned grassland.

The supply of soil respiration with recent photoassimilates is an important and fast pathway for respiratory loss of carbon (C). To date it is unknown how drought and land‐use change interactively influence the dynamics of recent C in soil‐respired CO2. In an in situ common‐garden experiment, we exposed soil‐vegetation monoliths from a managed and a nearby abandoned mountain grassland to an experimental drought. Based on two 13CO2 pulse‐labelling campaigns, we traced recently assimilated C in soil respiration during drought, rewetting and early recovery. Independent of grassland management, drought reduced the absolute allocation of recent C to soil respiration. Rewetting triggered a respiration pulse, which was strongly fuelled by C assimilated during drought. In comparison to the managed grassland, the abandoned grassland partitioned more recent C to belowground respiration than to root C storage under ample water supply. Interestingly, this pattern was reversed under drought. We suggest that these different response patterns reflect strategies of the managed and the abandoned grassland to enhance their respective resilience to drought, by fostering their resistance and recovery respectively. We conclude that while severe drought can override the effects of abandonment of grassland management on the respiratory dynamics of recent C, abandonment alters strategies of belowground assimilate investment, with consequences for soil‐CO2 fluxes during drought and drought‐recovery.

Regulating the nutrient release rates from proteinaceous agricultural byproducts using organic amendments and its effect on soil chemical and microbiological properties

Meat and bone meal (MBM) is a byproduct of the rendering industry and is considered an excellent potential organic fertilizer due to its balanced availability of nutrients. However, rapid nutrient mineralization of the MBM that is less synchronized with crop demand, could lead to significant nutrient losses, necessitating measures to modify the mineralization rates of MBM. Here we tested the influence of two natural nitrification inhibitors (NIs; neem cake and karanja cake) on the mineralization of carbon (C), nitrogen (N), and phosphorus (P) from MBM, the associated soil potential enzymatic activity, microbial abundance and broad composition and the influence of these process on plant growth. MBM mineralized quickly, with 35% mineralization of the applied N within the first 5 days of incubation. NIs reduced nitrification rate of MBM by ~ 40% and increased the retention of NH4+ (~ 35%) in soil compared with MBM only. Soil CO2 respiration, potential enzymatic activity and microbial abundance were similar in the MBM with and without NIs, suggesting a low negative effect of NIs on the microbial growth and functionality. MBM exhibits a slow P mineralization rate, with an increase in soil available P was observed only at later sampling points (36 days after incubation) with solubilization of a fraction of Ca-P. P mineralization rates were similar between the MBM with and without NIs. MBM with and without NIs was equally effective in maintaining the plant growth and biomass, which were similar to inorganic fertilizers. Our study suggests that MBM blended with NIs could increase the crop nutrient use efficiency via lowering N losses, while improving soil microbiological health.

Low CO2 levels of the entire Pleistocene epoch

Quantifying ancient atmospheric pCO2 provides valuable insights into the interplay between greenhouse gases and global climate. Beyond the 800-ky history uncovered by ice cores, discrepancies in both the trend and magnitude of pCO2 changes remain among different proxy-derived results. The traditional paleosol pCO2 paleobarometer suffers from largely unconstrained soil-respired CO2 concentration (S(z)). Using finely disseminated carbonates precipitated in paleosols from the Chinese Loess Plateau, here we identified that their S(z) can be quantitatively constrained by soil magnetic susceptibility. Based on this approach, we reconstructed pCO2 during 2.6–0.9 Ma, which documents overall low pCO2 levels (<300 ppm) comparable with ice core records, indicating that the Earth system has operated under late Pleistocene pCO2 levels for an extended period. The pCO2 levels do not show statistically significant differences across the mid-Pleistocene Transition (ca. 1.2–0.8 Ma), suggesting that CO2 is probably not the driver of this important climate change event.

Predicting Cool‐Season Turfgrass Response with Solvita Soil Tests, Part 2: CO2–Burst Carbon Concentrations

Current turfgrass fertilizer recommendations do not account for plant‐available soil N mineralized from labile C fractions. The Solvita Soil CO2–Burst (SSCB) test can measure mineralizable C via soil CO2 respiration. This study was conducted across 3 yr (2014–2016) in Connecticut to determine: (i) if SSCB–C concentrations are correlated to responses from predominately Kentucky bluegrass (Poa pratensis L.) and tall fescue [Schedonorus arundinaceus (Schreb.) Dumort.] lawns, and (ii) the probability of turfgrass responses being equal to or greater than responses from common urea rates in relation to SSCB–C concentrations. Randomized complete block design field experiments were set out with 23 rates of organic fertilizer (0–2000 kg N ha−1 yr−1) and four different rates of urea (50, 100, 150, and 200 kg N ha−1 yr−1). Yearly spring soil samples were analyzed for SSCB–C concentrations and correlated with turfgrass responses. Growth and quality responded positively and linearly (P &lt; 0.001) to SSCB–C concentrations, but variability was high and correlations were relatively weak. When spring soil SSCB–C concentrations were ≥91, 113, 166, and 211 mg kg−1, there was a ≥90% probability that overall combined responses across species and variables would be equal to or greater than responses obtained from urea rates of 50, 100, 150, and 200 kg N ha−1 yr−1, respectively. The SSCB test has promise for predicting the probability of soils supporting turfgrass whose performance equals or exceeds benchmark values. This would be helpful in guiding N fertilization, but high variability within the test may limit its predictive ability.

Temporal and spatial variability in soil CO2 efflux in the patagonian steppe

Soil respiration is a major flux of CO2 to the atmosphere. Despite its significance there is a limited understanding of its magnitude, controlling factors and how it varies over time and space in arid ecosystems. We evaluated the temporal pattern of soil CO2 efflux and their response to rain pulses in a patagonian steppe, taking into account the spatial heterogeneity (bare soil and vegetated patches). We measured soil CO2 efflux in bare soil and vegetated patches along the year. We also analyzed physical and chemical soil traits, root density and heterotrophic bacterial count. Soil water content and temperature exhibited seasonal variability and it was larger in bare soil patches than in vegetated patches. Root density, organic matter and phosphorus were higher in vegetated patches than in bare soil. CO2 efflux was 48% higher in vegetated patches than in bare soil patches. Soil CO2 efflux decreased from summer to winter, reaching its maximum value (about 0.6 μmol m2 s−1) in spring. In both patch types, soil CO2 efflux was explained by the interaction between soil temperature and soil water content. Soil CO2 efflux also was positively correlated with soil root density. Bare soil and vegetated patches exhibited distinct response to a rain pulses. Vegetated patches were highly sensitive to rainfall events, generating a large CO2 pulse, returning to previous values after three days. Bare soil CO2 efflux did not exhibit significant changes after a rain pulse. In patagonian arid ecosystems, the seasonal variation in soil respiration is explained mainly by the interaction between soil temperature and water content. Bare soil patches had higher water content but lower root density resulting in lower soil CO2 respiration than vegetated patches. However, at ecosystem level the contribution of bare soil to total soil CO2 efflux was similar to the contribution of vegetated patches because bare soil cover is 65% in the study area. Changes in the number of small rain events as well as changes in plant cover could have large consequences on soil ecology and biochemistry in dry and heterogeneous ecosystems.

Effect of catchment lithology on dissolved inorganic carbon budgets in suburban streams of Baltimore, Maryland, during rainfall minima

Urbanization has the potential to affect riverine carbon exports, but relatively few studies have evaluated the potential effect of lithology on carbon fluxes in urban settings. To address this gap, four first-order streams in the Baltimore metropolitan area exhibiting different levels of impervious surfaces and catchment lithologies were examined for a span of ten weeks during a period of rainfall minima with the purpose of identifying sources and magnitudes of inorganic carbon transported by these streams during base flow conditions. Discharge, alkalinity, pH, temperature, and dissolved oxygen were measured in situ, whereas the carbon isotopic composition of dissolved inorganic carbon (DIC) was determined in the laboratory. Abundances of DIC and pCO2 were estimated from the collected data, revealing that the stream with an increased forest coverage and a calcareous catchment consistently had the highest values for DIC, pCO2, alkalinity, and stable isotope ratios. DIC yields for the four studied streams were relatively low, ranging from 2.6 to 21.8 mmol C/m2-yr, and calculated pCO2 evasion rates were some of the lowest recorded values in temperate and boreal regions, ranging from 184 to 6451 g C/day. These low values possibly resulted from the low rainfall amount that prevailed during the sampling period, which limited both the transfer of soil-derived DIC to the studied streams and the subsequent emission of CO2 to the atmosphere. Stable isotope data linearly correlated with DIC, and this relation could reflect the lithological control of inorganic carbon in the studied streams, with a 13C-enriched source of DIC probably representing the dissolution of calcareous metamorphic rocks and some contribution of soil-respired CO2 and with a 13C-depleted source interpreted to result from a predominant contribution of soil-respired CO2. Thus, our results point to the dominant effect of catchment lithology in regulating stream DIC budgets in the studied suburban streams during low discharge conditions.

CO2 Flux and C Balance due to the Replacement of Bare Soil with Agro-Ecological Service Crops in Mediterranean Environment

Intensive agriculture practices often results in decomposition of organic matter, thus causing soil CO2 emissions. Agro-ecological service crop could be profitably cultivated to improve soil characteristics and reduce CO2 emissions under Mediterranean environment. Two-year field trials were conducted in central Italy. The treatments were three agro-ecological service crops (hairy vetch, oat, and oilseed rape) and a no-service cover. Plant development, soil characteristics, and CO2 emissions were measured. Oat and oilseed rape showed a rapid growth, while hairy vetch started to grow rapidly only after the cold period. Soil CO2 emissions trend was similar among the agro-ecological service crops and tended to decrease during the cold period, then gradually increased until April when warm temperatures were observed. The high soil CO2 emissions and respiration index observed in hairy vetch probably stimulated mineral nutrients, especially nitrogen, to become more available in the soil compared to oat and oilseed rape throughout the decomposition of soil organic matter. These results confirmed that the cultivation of agro-ecological service crops, especially hairy vetch, could represent a suitable strategy for enhancing carbon sequestration and lead to a mitigation of CO2 emissions during the fallow period and could thus contribute to the climate change mitigation.

Field-to-farm gate greenhouse gas emissions from corn stover production in the Midwestern U.S.

Measured field data were used to compare two allocation methods on life cycle greenhouse gas emissions from corn (Zea mays L.) stover production in the Midwest U.S. We used publicly-available crop yield, nitrogen fertilizer, and direct soil nitrous oxide emissions data from the USDA-ARS Resilient Economic Agricultural Practices research program. Field data were aggregated from 9 locations across 26 site-years for 3 stover harvest rates (no removal; moderate removal – 3.1 Mg ha−1; high removal – 7.2 Mg ha−1) and 2 tillage practices (conventional; reduced/no-till). Net carbon uptake by crops was computed from measured plant carbon content. Monte Carlo simulations sampled input distributions to assess variability in farm-to-gate GHG emissions. The base analysis assumed no change in soil organic carbon stocks. In all cases, net CO2 uptake during crop growth and soil-respired CO2 dominated system emissions. Emissions were most sensitive to co-product accounting method, with system expansion emissions ∼15% lower than mass allocation. Regardless of accounting method, lowest emissions occurred for a moderate removal rate under reduced/no-till management. The absence of correlations between N fertilization rate and stover removal rate or soil N2O emissions in this study challenges the use of such assumptions typically employed in life cycle assessments Storage of all carbon retained on the field as SOC could reduce emissions by an additional 15%. Our results highlight how variability in GHG emissions due to location and weather can overshadow the impact of farm management practices on field-to-farm gate emissions.