Seasonal Dynamics of Soil CO<Subscript>2</Subscript> Concentration and CO<Subscript>2</Subscript> Fluxes from the Soil of the Former Lake Texcoco,Mexico

Seasonal changes of the soil CO₂ concentration and the rate of CO₂ fluxes emission from the soil formed on the sediments of the former Lake Texcoco, which occupied a significant part of the Mexico Valley until the mid-17th century, were studied. The soils (Fluvic Endogleyic Phaeozems) were characterized by a low CO₂ fluxes rate, which is related to their high alkalinity. The mean values of soil respiration were 6.0–14.1 mg C/(m² h) depending on vegetation type, which corresponds to 60–157 g C/(m² yr). The contribution of plants to the CO₂ fluxes insignificantly varied by seasons and depended on the species composition of vegetation. The soil CO₂ concentration and soil respiration in eucalypt (Eucalyptus globulus Labill.) plantation were two times higher than those in the grass–subshrub area, the ground cover of which consisted of Distichlis spicata (L.) Greene and Suaeda nigra (Raf.) J.F. Macbr. species. This can be related to the significant volumes of gas production during the respiration of eucalypt roots and associated rhizosphere community. The contribution of the root systems of grass cover to the soil CO₂ fluxes in eucalypt plantation slightly varied within the year and was equal to 24% on the average. In the grass–subshrub area, its value varied from 41% in the cold season to 60% in the warm season. The spatial variability of soil CO₂ concentration and its flux rate to the atmosphere was due to the differences in plant species composition and hydrothermal conditions, and their temporal trend was closely related to the seasonal accumulation of plant biomass and soil temperature.     

Effect of Stover Management and Nitrogen Fertilization on N<Subscript>2</Subscript>O and CO<Subscript>2</Subscript> Emissions from Irrigated Maize in a High Nitrate Mediterranean Soil

A high soil nitrogen (N) content in irrigated areas quite often results in environmental problems. Improving the management practices of intensive agriculture can mitigate greenhouse gas (GHG) emissions. This study compared the effect of maize stover incorporation or removal together with different mineral N fertilizer rates (0, 200 and 300 kg N ha^?1) on the emission of nitrous oxide (N₂O) and carbon dioxide (CO₂) on a sprinkler-irrigated maize (Zea mays L.). The trail was conducted in the Ebro Valley (NE Spain) in a high nitrate-N soil (i.e. 200 g NO₃–N kg^?1). Nitrous oxide and CO₂ emissions were sampled weekly using a semi-static closed chamber and quantified using the photoacoustic technique in 2011 and 2012. Applying sidedress N fertilizer tended to increase N₂O emissions whereas stover incorporation did not have any clear effect. Nitrification was probably the main process leading to N₂O. Denitrification was limited by the low soil moisture content (WFPS <?54%), due to an adequate irrigation management. Emissions ranged from ??0.11 to 0.36% of the N applied, below the IPCC (2007) values. Nitrogen fertilization tended to reduce CO₂ emission, but only in 2011. Stover incorporation increased CO₂ emission. Nitrogen use efficiency decreased with increasing mineral fertilizer supply. The application of N in high N soils of the Ebro Valley is not necessary until the soil restores a normal mineral N content, regardless of stover management. This will combine productivity with keeping N₂O and CO₂ emissions under control provided irrigation is adequately managed. Testing soil NO₃ ^?–N contents before fertilizing would improve N fertilizer recommendations.     

Effects of biochar addition on N<Subscript>2</Subscript>O and CO<Subscript>2</Subscript> emissions from two paddy soils

Impacts of biochar addition on nitrous oxide (N₂O) and carbon dioxide (CO₂) emissions from paddy soils are not well documented. Here, we have hypothesized that N₂O emissions from paddy soils could be depressed by biochar incorporation during the upland crop season without any effect on CO₂ emissions. Therefore, we have carried out the 60-day aerobic incubation experiment to investigate the influences of rice husk biochar incorporation (50 t ha⁻¹) into two typical paddy soils with or without nitrogen (N) fertilizer on N₂O and CO₂ evolution from soil. Biochar addition significantly decreased N₂O emissions during the 60-day period by 73.1% as an average value while the inhibition ranged from 51.4% to 93.5% (P < 0.05–0.01) in terms of cumulative emissions. Significant interactions were observed between biochar, N fertilizer, and soil type indicating that the effect of biochar addition on N₂O emissions was influenced by soil type. Moreover, biochar addition did not increase CO₂ emissions from both paddy soils (P > 0.05) in terms of cumulative emissions. Therefore, biochar can be added to paddy fields during the upland crop growing season to mitigate N₂O evolution and thus global warming.     

Reducing CH<Subscript>4</Subscript> and CO<Subscript>2</Subscript> emissions from waterlogged paddy soil with biochar

Purpose  

A potential means to diminish increasing levels of CO₂ in the atmosphere is the use of pyrolysis to convert biomass into biochar, which stabilizes the carbon (C) that is then applied to soil. Before biochar can be used on a large scale, especially in agricultural soils, its effects on the soil system need to be assessed. This is especially important in rice paddy soils that release large amounts of greenhouse gases to the atmosphere.     

Spatio-temporal prediction inside a free-air CO<Subscript>2</Subscript> enrichment system

The Japanese RiceFACE (Free-Air CO₂ Enrichment) project was a three-year investigation into the effect of elevated CO₂ on rice. Four rings were built to emit elevated levels of CO₂. The aim of the FACE system is to provide a level of CO₂ enrichment 200 ppm above tmbient throughout the plot, without changing any other aspect of the microclimate within the plot. However, there can be substantial spatial variation in the CO₂ level from the center to the edges of the plots. One of our main objectives was to predict the seasonal mean levels of CO₂ for multiple subregions within the plots. However, the dataset was very large and followed a nonnormal distribution. Furthermore, the mean and variance were nonstationary. To overcome these difficulties daily means were used rather than individual measurements, the mean was modeled with multiple covariates that varied over both time and space, and the variance was modeled as an increasing function of the square of the distance from the center of the plot. A separable space-time covariance structure was used, and estimation was performed using nonlinear methods, REML, and EGLS. Finally, cross-validation was used to assess the validity of the model.     

Nitrogen rhizodeposition of young wheat plants under elevated CO<Subscript>2</Subscript> and drought stress

The objective of this study was to determine the effect of drought stress and elevated CO₂ concentrations around the shoots on N rhizodeposition of young wheat plants. In a pot experiment, the plant N pool was labeled through ¹⁵NH₃ application to shoots at nontoxic NH₃ concentrations, and the impact of low water supply (40% field capacity), elevated CO₂ (720 μmol mol⁻¹ CO₂), and the combination of both factors on the ¹⁵N distribution was studied. Total ¹⁵N rhizodeposition ranged from 5 to 11% of the total ¹⁵N recovered in the plant/soil system. Elevated CO₂ concentration as well as drought stress increased the belowground transport of N and increased the relative portion of N rhizodeposition on total ¹⁵N in the plant/soil system. However, while the increased N rhizodeposition with elevated CO₂ was the result of increased total belowground N transport, drought stress additionally increased the portion of ¹⁵N found in rhizodeposition vs roots. Elevated CO₂ intensified the effect of drought stress. The percentage of water soluble ¹⁵N in the ¹⁵N rhizodeposition was very low under all treatments, and it was significantly decreased by the drought-stressed treatments.     

N<Subscript>2</Subscript>O,CO<Subscript>2</Subscript>, Production,and C Sequestration in Vineyards: a Review

Even if it is less polluting than other farm sectors, grape growing management has to adopt measures to mitigate greenhouse gas (GHG) emissions and to preserve the quality of grapevine by-products. In viticulture, by land and crop management, GHG emissions can be reduced through adjusting methods of tillage, fertilizing, harvesting, irrigation, vineyard maintenance, electricity, natural gas, and transport until wine marketing, etc. Besides CO₂, nitrous oxide (N₂O) and methane (CH₄), released from fertilizers and waste/wastewater management are produced in vineyards. As the main GHG in vineyards, N₂O can have the same harmful action like large quantities of CO₂. Carbon can be found in grape leaves, shoots, and even in fruit pulp, roots, canes, trunk, or soil organic matter. C sequestration in soil by using less tillage and tractor passing is one of the efficient methods to reduce GHG in vineyards, with the inconvenience that many years are needed for detectable changes. In the last decades, among other methods, cover crops have been used as one of the most efficient way to reduce GHG emissions and increase fertility in vineyards. Even if we analyze many references, there are still limited information on practical methods in reducing emissions of greenhouse gases in viticulture. The aim of the paper is to review the main GHG emissions produced in vineyards and the approached methods for their reduction, in order to maintain the quality of grapes and other by-products.     

An assessment of factors controlling N<Subscript>2</Subscript>O and CO<Subscript>2</Subscript> emissions from crop residues using different measurement approaches

Management of plant residues plays an important role in maintaining soil quality and nutrient availability for plants and microbes. However, there is considerable uncertainty regarding the factors controlling residue decomposition and their effects on greenhouse gas (GHG) emissions from the soil. This uncertainty is created both by the complexity of the processes involved and limitations in the methodologies commonly used to quantify GHG emissions. We therefore investigated the addition of two soil residues (durum wheat and faba bean) with similar C/N ratios but contrasting fibres, lignin and cellulose contents on nutrient dynamics and GHG emission from two contrasting soils: a low-soil organic carbon (SOC), high pH clay soil (Chromic Haploxerert) and a high-SOC, low pH sandy-loam soil (Eutric Cambisol). In addition, we compared the effectiveness of the use of an infrared gas analyser (IRGA) and a photoacoustic gas analyser (PGA) to measure GHG emissions with more conventional gas chromatography (GC). There was a strong correlation between the different measurement techniques which strengthens the case for the use of continuous measurement approaches involving IRGA and PGA analyses in studies of this type. The unamended Cambisol released 286% more CO₂ and 30% more N₂O than the Haploxerert. Addition of plant residues increased CO₂ emissions more in the Haploxerert than Cambisol and N₂O emission more in the Cambisol than in the Haploxerert. This may have been a consequence of the high N stabilization efficiency of the Haploxerert resulting from its high pH and the effect of the clay on mineralization of native organic matter. These results have implication management of plant residues in different soil types.     

Daily and seasonal dynamics of CO<Subscript>2</Subscript> fluxes from soils under different stands of monsoon tropical forest

The analysis of daily, seasonal, and annual dynamics of CO₂ emission from soils under different stands of monsoon tropical tall-tree forest was performed on the basis of field observations conducted at the Russian-Vietnamese Tropical Research and Technology Center of the Russian Academy of Sciences. Under a tropical climate, the main factors responsible for the rate of carbon dioxide emission from the soils are shown to be the soil type and the topographic position of the area studied along with the type of vegetation. Depending on these factors, the rate of CO₂ emission from the soils was 65–178 mg C/(m² h) during the dry season and 123–259 mg C/(m² h) during the wet season. The daily dynamics of CO₂ emissions from the soils of the tropical zone was weakly pronounced in both the wet and the dry season owing to the insignificant diurnal fluctuations of soil temperature. The investigations carried out allowed making an expert evaluation of the annual CO₂ fluxes from the soils under different stands of monsoon tropical tall-tree forest in southern Vietnam. They amounted to 900–2000 g C/(m² yr) depending on the forest type.     

Influence of Biochar Addition on the Denitrification Process and N<Subscript>2</Subscript>O Emission in Cd-Contaminated Soil

The aim of this study was to investigate the effect of biochar addition on the denitrification process and N₂O emission in Cd-contaminated soil. Four different biochars, i.e., dairy manure and rice straw pyrolyzed at 350 and 550 °C, respectively, were added into a Cd-contaminated soil and incubation experiments were conducted for 8 weeks. Results showed that Cd had an inhibitory effect on denitrifying reductase enzymes and reduced the abundance of functional genes. On the contrary, amendment with the biochars increased denitrifying enzyme activity and gene abundance, and thus, enhanced the denitrification process. Labile carbon (C) in the biochar-amended soil, which was calculated based on the two-pool exponential model, was the key factor to facilitate this process. As a less important factor, elevated soil pH by biochar addition also increased denitrifying activity as well as the nosZ abundance. Decrease of Cd bioavailability by the biochar addition was beneficial to the denitrification process. Addition of the biochars with higher amount of NO₃ ^?-N, especially the rice straw-derived biochars, increased cumulative N₂O emission by more than ten times relative to the Cd-contaminated soil. With the great amount of labile C and NO₃ ^?-N, the treatment of biochars prepared at 350 °C released the larger amount of CO₂ and N₂O than other treatments. The biochar addition could totally release the heavy metal stress and restore the Cd-contaminated soil in terms of bacterial community.     

The effect of moisture on nitrous oxide emissions from soil and the N<Subscript>2</Subscript>O/(N<Subscript>2</Subscript>O+N<Subscript>2</Subscript>) ratio under laboratory conditions

Nitrous oxide (N₂O) contributes to greenhouse effect; however, little information on the consequences of different moisture levels on N₂O/(N₂O+N₂) ratio is available. The aim of this work was to analyze the influence of different soil moisture values and thus of redox conditions on absolute and relative emissions of N₂O and N₂ at intact soil cores from a Vertic Argiudoll. For this reason, the effect of water-filled porosity space (WFPS) values of soil cores of 40, 80,100, and 120% (the last one with a 2-cm surface water layer) was investigated. The greatest N₂O emission occurred at 80% WFPS treatment where conditions were not reductive enough to allow the complete reduction to N₂. The N₂O/(N₂O+N₂) ratio was lowest (0–0.051) under 120% WFPS and increased with decreasing soil moisture content. N₂O/(N₂O+N₂) ratio values significantly correlated with soil Eh; redox conditions seemed to control the proportion of N gases emitted as N₂O. N₂O emissions did not correlate satisfactorily with N₂O/(N₂O+N₂) ratio values, whereas they were significantly explained by the amount of total N₂O+N₂ emissions.     

Procedural Approaches to Field Determination of Root and Microbial Respiration Contribution to CO<Subscript>2</Subscript> Emission by Permafrost-Affected Soils

In the discontinuous cryolithozone in the north of Western Siberia in forest and tundra biogeocoenoses, two field methods for individual determination of root and microbial soil respiration were tested: plant shading and root exclusion (comparison of the plots with vegetation and without it). The proportion of of root respiration in the total soil respiration in the forest biogeocoenosis was 7–50%; in the tundra, 10–50%. The plant shading method has been physiologically substantiated, is the least time-consuming, and the least damaging to soil function (moisture and temperature do not change). The proposed modification of the method (root exclusion on natural objects) demonstrated a satisfactory result, but it is not universal due to the specifics of objects.     

Soil N<Subscript>2</Subscript>O emissions and N<Subscript>2</Subscript>O/(N<Subscript>2</Subscript>O+N<Subscript>2</Subscript>) ratio as affected by different fertilization practices and soil moisture

The objective of this work was to evaluate the effect of the chemical nature and application frequency of N fertilizers at different moisture contents on soil N₂O emissions and N₂O/(N₂O+N₂) ratio. The research was based on five fertilization treatments: unfertilized control, a single application of 80 kg ha⁻¹ N-urea, five split applications of 16 kg ha⁻¹ N-urea, a single application of 80 kg ha⁻¹ N–KNO₃, five split applications of 16 kg ha⁻¹ N–KNO₃. Cumulative N₂O emissions for 22 days were unaffected by fertilization treatments at 32% water-filled pore space (WFPS). At 100% and 120% WFPS, cumulative N₂O emissions were highest from soil fertilized with KNO₃. The split application of N fertilizers decreased N₂O emissions compared to a single initial application only when KNO₃ was applied to a saturated soil, at 100% WFPS. Emissions of N₂O were very low after the application of urea, similar to those found at unfertilized soil. Average N₂O/(N₂O+N₂) ratio values were significantly affected by moisture levels (p = 0.015), being the lowest at 120% WFPS. The N₂O/(N₂O+N₂) ratio averaged 0.2 in unfertilized soil and 0.5 in fertilized soil, although these differences were not statistically significant.     

Production of CO<Subscript>2</Subscript> by surface and buried soils of the steppe zone under native and moistened conditions

Modern light chestnut and chestnut soils and their analogues buried under steppe kurgans in the southeastern part of the Russian Plain were studied in order to determine the rates of the CO₂ production by these soils under the native (with the natural moisture content) and moistened (60% of the total water capacity) conditions. It was found that the rates of the CO₂ production by the soil samples in the native state are relatively close to one another and vary from 0.3 to 1.4 μg of C/100 g of soil/h. The rates of the CO₂ production in the moistened state increased by two orders of magnitude for the modern surface soils and by an order of magnitude for the buried soils.     

Seasonal and Daily Dynamics of the CO<Subscript>2</Subscript> Emission from Soils of <Emphasis Type="Italic">Pinus koraiensis</Emphasis> Forests in the South of the Sikhote-Alin Range

The presented study shows the results of measuring soil respiration in typical burozems (Dystric Cambisols) under mixed Korean pine–broadleaved forests in the southern part of the Primorskii (Far East) region of Russia growing under conditions of monsoon climate. The measurements were performed in 2014–2016 by the chamber method with the use of a portable infrared gas analyzer. Relative and total values of the CO₂ efflux from the soil surface on four model plots were determined. The intensity of summer emission varied from 2.25 to 10.97 μmol/(m² s), and the total CO₂ efflux from the soils of four plots varied from 18.84 to 25.56 mol/m². It is shown that a larger part of seasonal variability in the soil respiration is controlled by the soil temperature (R² = 0.5–0.7); the soil water content also has a significant influence on the CO₂ emission determining about 10% of its temporal variability. The daily dynamics of soil respiration under the old-age (200 yrs) forest have a significant relationship with the soil temperature (R² = 0.51). The pyrogenic transformation of Pinus koraiensis forests into low-value oak forests is accompanied by an increase in the СО₂ efflux from the soil.     

The fungal and bacterial biomass (selective inhibition) and the production of CO<Subscript>2</Subscript> and N<Subscript>2</Subscript>O by soddy-podzolic soils of postagrogenic biogeocenoses

In the humus horizon of soddy-podzolic soils of postagrogenic cenoses and primary forests, the contributions of the fungi and bacteria were determined by the selective inhibition of the substrate-induced respiration (SIR) by antibiotics; the basal (microbial) respiration and the net-produced nitrous oxide (N₂O) were also determined. The procedure of the SIR separation using antibiotics (cycloheximide and streptomycin) into the fungal and bacterial components was optimized. It was shown that the fungi: bacteria ratio was 1.58, 2.04, 1.55, 1.39, 2.09, and 1.86 for the cropland, fallow, and different-aged forests (20, 45, 90, and 450 years), respectively. The fungal and bacterial production of CO₂ in the primary forest soil was higher than in the cropland by 6.3 and 11.4 times, respectively. The production of N₂O in the soils of the primary and secondary (90-year-old) forests (3 and 7 ng N-N₂O/g soil per hour, respectively) was 2–13 times lower than in the postagrogenic cenoses, where low values were also found for the microbial biomass carbon (C_mic), its components (the C_mic-bacteria and C_mic-fungi), and the portion of C_mic in the organic carbon of the soil. A conclusion was drawn about the misbalance of the microbial processes in the overgrown cropland accompanied by the increased production of N₂O by the soil during its enrichment with an organic substrate (glucose).     

Effects of long-term exposure to enriched CO<Subscript>2</Subscript> on the nutrient-supplying capacity of a grassland soil

Altered soil nutrient cycling under future climate scenarios may affect pasture production and fertilizer management. We conducted a controlled-environment study to test the hypothesis that long-term exposure of pasture to enriched carbon dioxide (CO₂) would lower soil nutrient availability. Perennial ryegrass was grown for 9 weeks under ambient and enriched (ambient + 120 ppm) CO₂ concentrations in soil collected from an 11.5-year free air CO₂ enrichment experiment in a grazed pasture in New Zealand. Nitrogen (N) and phosphorus (P) fertilizers were applied in a full factorial design at rates of 0, 12.5, 25 or 50 kg N ha⁻¹ and 0, 17.5 or 35 kg P ha⁻¹. Compared to ambient CO₂, under enriched CO₂ without P fertilizer, total plant biomass did not respond to N fertilizer, and tissue N/P ratio was increased indicating that P was co-limiting. This limitation was alleviated with the lowest rate of P fertilizer (17.5 kg P ha⁻¹). Plant biomass in both CO₂ treatments increased with increasing N fertilizer when sufficient P was available. Greater inputs of P fertilizer may be required to prevent yield suppression under enriched CO₂ and to stimulate any response to N.     

Determination of root and microbial contributions to the CO<Subscript>2</Subscript> emission from soil by the substrate-induced respiration method

The contributions of root and microbial respiration to the CO₂ emission from the surface of gray forest and soddy-podzolic soils under meadow and forest vegetation were determined in field and laboratory experiments. In the field, a new modification of the substrate-induced respiration (SIR) method was applied. According to this method, the contribution of root respiration was estimated at 41–50% for meadow cenoses and 33% for forest cenoses; similar values were obtained in the course of separate incubation of roots and soil in laboratory (42–57% and 29–32%, respectively) and with the use of the laboratory version of the SIR method (35–40% and 21–31%, respectively). The analysis of difference between the values of root respiration and microbial respiration obtained by the field and laboratory methods for the same experimental plots and the comparison of advantages and disadvantages of these methods made it possible to outline the ways for the further improvement of the field version of the SIR method.     

Preparation of Highly Efficient CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/Zn<Subscript>2</Subscript>SnO<Subscript>4</Subscript> Composite Photocatalyst for the Degradation of Rhodamine B Dye from Aqueous Solution

CoFe₂O₄/Zn₂SnO₄ composite was synthesized using a simple two-step process and applied as a novel-efficient photocatalyst for the rhodamine B degradation from aqueous solution. Characterization techniques such as X-ray diffraction (XRD), N₂ adsorption-desorption isotherms, scanning electron microscopy (SEM), EDS analysis, and diffuse reflectance spectroscopy were employed in order to investigate the physical and chemical properties of composite. Higher values of the specific surface area, pore volume and diameter, and a smaller band-gap energy promoted a greater catalytic activity of CoFe₂O₄/Zn₂SnO₄ composite when compared to Zn₂SnO₄. A rapid decolorization of dye solution was observed at 40 min of reaction using the CoFe₂O₄/Zn₂SnO₄ catalyst, being 2.5 times faster than the Zn₂SnO₄ alone. Therefore, the CoFe₂O₄/Zn₂SnO₄ composite shows extraordinarily high photocatalytic activity toward the degradation of rhodamine B dye from aqueous solution.     

Carbon turnover in the rhizosphere under continuous plant labeling with <Superscript>13</Superscript>CO<Subscript>2</Subscript>: Partitioning of root,microbial, and rhizomicrobial respiration

The input of labeled C into the pool of soil organic matter, the CO₂ fluxes from the soil, and the contribution of root and microbial respiration to the CO₂ emission were studied in a greenhouse experiment with continuous labeling of oat plants with ¹³CO₂ using the method of the natural ¹³C abundance in the air. The carbon of the microbial biomass composed 56 and 39% of the total amounts of ¹³C photoassimilates in the rhizosphere and in the bulk soil, respectively. The contribution of root respiration to the CO₂ emission from the soil reached 61–92%, including 4–23% of the rhizomicrobial respiration. The contribution of the microbial respiration to the total CO₂ emission from the soil varied from 8 to 39%. The soil organic matter served as the major carbon-containing substrate for microorganisms in the bulk soil and in the rhizosphere: 81–91% of the total amount of carbon involved in the microbial metabolism was derived from the soil organic matter.