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 emission of carbon dioxide from soils of the Pasvik nature reserve in the Kola Subarctic

The emission of carbon dioxide (CO₂) from podzols (Albic Podzols (Arenic)) and the factors controlling its spatiotemporal variability in the forest ecosystems of the Pasvik Reserve in the Kola Subarctic are characterized. Relatively favorable climatic conditions beyond the polar circle in summer are responsible for intensive soil respiration. The type of forest affects the emission of CO₂ from the soil surface. The lowest rate of the CO₂ emission is typical of the soils under lichen pine forest (105–220 mg C/(m² h) or 180 g C/m² during the summertime). Higher rates are observed for the soils under green moss pine (170–385 mg C/(m² h) or 360 g C/m² during the summertime) and birch (190–410 mg C/(m² h) or 470 g C/m² during the summertime) forests. This may related to a higher contribution of root respiration (44, 88, and 67%, respectively). Soil respiration and the contribution of root respiration to it increase with an increase in the canopy density; mass of small roots; microbial biomass; depth of the stony layer; soil moistening; and the contents of available carbon, nitrogen, phosphorus, and potassium compounds. At the same time, they decrease with an increase in the portion of lichens in the ground cover. The seasonal dynamics are characterized by the CO₂ emission maximums in the summer and fall and minimum in the spring. The daily dynamics are smoothed under conditions of the polar day.     

Carbon dioxide emission from the soil surface in a bilberry-sphagnum pine forest of the Middle Taiga

The dynamics of the carbon dioxide emissions from the surface of a gleyic iron-illuvial sandy peat podzolic soil under a mature bilberry-sphagnum pine forest were studied during the growing seasons of 2008–2010. The maximum rates of the CO₂ emission were observed in late July-early August, and the minimum rates were in October. In the hot summer of 2010, an additional maximum was observed in June. A close positive correlation existed between the intensity of the CO₂ emission and the soil temperature (r = 0.71, α = 0.05), whereas no significant correlation was found between the CO₂ emission and the soil water content. The coefficient of multiple correlation between the rate of the CO₂ emission and the hydrothermic soil characteristics reached 0.57 (at α = 0.05). The total CO₂ emission from the soil surface during the growing season was estimated at 68–100 g of C m^?2.     

Carbon dioxide emission from the surface of podzolic soils

The regularities of the seasonal dynamics of the CO₂ emission from the surface of a podzolic soil under a bilberry pine forest of the middle taiga were revealed. In mid-May, after the snow melt, the CO₂ emission was 0.10–0.20 g of CO₂/m² per h. Then, the intensity of the CO₂ emission increased, reached its maximum (1.0 to 1.5 g of CO₂/m² per h) in July–August, and decreased down to 0.04–0.10 g of CO₂ g/m² per h in mid-October. The correlation between the rate of the CO₂ emission and the temperature and moisture of the soil was positive and negative: r = 0.34 to 0.91 and ?0.44 to ?0.86, respectively. According to the empirical model, 2.26–2.69 t of C-CO₂/ha were emitted during the warm time of the year.     

Repeated drying–rewetting cycles and their effects on the emission of CO2, N2O,NO, and CH4 in a forest soil

Prolonged summer droughts due to climate change are expected for this century, but little is known about the effects of drying and wetting on biogenic trace‐gas fluxes of forest soils. Here, the response of CO₂, N₂O, NO, and CH₄ fluxes from temperate forest soils towards drying–wetting events has been investigated, using undisturbed soil columns from a Norway spruce forest in the “Fichtelgebirge”, Germany. Two different types of soil columns have been used for this study to quantify the contribution of organic and mineral horizons to the total fluxes: (1) organic horizons (O) and (2) organic and mineral soil horizons (O+M). Three drying–wetting treatments with different rewetting intensities (8, 20, and 50 mm of irrigation d^–1) have been compared to a constantly moist control to estimate the influence of rainfall intensity under identical drying conditions and constant temperature (+15°C). Drought significantly reduced CO₂, N₂O, and NO fluxes in most cycles. Following rewetting, CO₂ fluxes quickly recovered back to control level in the O columns but remained significantly reduced in the O+M columns with total CO₂ fluxes from the drying–wetting treatment ranging approx. 80% of control fluxes. Fluxes of N₂O and NO remained significantly reduced in both O and O+M columns even after rewetting, with cumulative fluxes from drying–wetting treatments ranging between 20% and 90% of the control fluxes, depending on gas and cycle. Fluxes of CH₄ were small in all treatments and seem to play no significant role in this soil. No evidence for the release of additional gas fluxes due to drying–wetting was found. The intensity of rewetting had no significant effect on the CO₂, N₂O, NO, and CH₄ fluxes, suggesting that the length of the drought period is more important for the emission of these gases. We can therefore not confirm earlier findings that fluxes of CO₂, N₂O, and NO during wetting of dry soil exceed the fluxes of constantly moist soil.     

Microbiological transformation of carbon and nitrogen compounds in forest soils of Central Evenkia

It has been found that the total productivity of bacteria and micromycetes in the 0- to 50-cm layer of homogeneous cryozems (Cryosols) on slopes of northern and southern exposures varies from 1.2 to 1.4 t/ha, respectively, and the calculated content of microbial carbon varies in the range 0.7–0.9 t/ha. The respiratory activity of the upper soil layer is 2.5–2.6 μg C–CO₂/(g h); the potential methane formation capacity reaches 0.13 nmol CH₄/(m² day) for soils on slopes of northern exposure and 0.16 nmol CH₄/(m² day) for slopes of southern exposure. Accumulation of sorbed ammonium is recorded in the range 15–17 mg NH₄/100 g soil in summer. The increase of temperature in the upper horizons of soils on slopes of southern exposure by 5°C compared to the northern slopes results in only an insignificant increase in the emission of CO₂ and CH₄. The accumulation of sorbed ammonium and nitrate nitrogen in homogeneous cryozems during the vegetation period is comparable to that in gray forest soils of the southern taiga subzone of the Middle Siberia.     

Biotic and abiotic factors regulating forest floor CO2 flux across a range of forest age classes in the southern Appalachians

We measured forest floor CO₂ flux in three age classes of forest in the southern Appalachians: 20-year-old, 85-year-old, and old-growth. Our objectives were to quantify differences in forest floor CO₂ flux among age classes, and determine the relative importance of abiotic and biotic driving variables. Forest floor CO₂ flux was measured using an openflow infrared gas analyzer measurement system for 24 h periods and samples were taken every 2 months over a 2-year period. Litter/soil interface, soil temperature (5 cm depth), soil moisture (%), forest floor moisture (%), forest floor mass, fine root (2 mm) mass, coarse root mass (>2 mm), forest floor C and N (%), fine root C and N, coarse root C and N, and soil N and C were co-measured during each sample period. Results showed significant nonlinear relationships (r²=0.68 to 0.81) between litter/soil interface temperature and forest floor CO₂ flux for all three forest age classes, but no differences in temperature response parameters. These results indicated no differences in forest floor CO₂ flux among age classes. Considerable temporal variation in abiotic and biotic variables was observed within and among forests. Biotic variables correlated with forest floor CO₂ flux included indices of litter and root quality. Differences in biotic variables correlated with forest floor CO₂ flux among forests may have been related to shifts in the relative importance of heterotrophic and autotrophic respiration components to overall forest floor CO₂ flux.     

Influence of forest disturbance on CO2, CH4 and N2O fluxes from larch forest soil in the permafrost taiga region of eastern Siberia

Abstract

To evaluate the effect of increasing forest disturbances on greenhouse gas budgets in a taiga forest in eastern Siberia, CO₂, CH₄ and N₂O fluxes from the soils were measured during the growing season in intact, burnt and clear-felled larch forests (4–5 years after the disturbance). Soil temperature and moisture were higher at the two disturbed sites than at the forest site. A 64–72% decrease in the Q ₁₀ value of soil CO₂ flux from the disturbed sites compared with the forest site (5.92) suggested a reduction in root respiration and a dominance of organic matter decomposition at the disturbed sites. However, the cumulative CO₂ emissions (May–August) were not significantly different among the sites (2.81–2.90 Mg C ha^?1 per 3 months). This might be because decreased larch root respiration was compensated for by increased organic matter decomposition resulting from an increase in the temperature and root respiration of invading vegetation at the disturbed sites. The CH₄ uptake (kg C ha^?1 per 4 months [May–September]) at the burnt site was significantly higher (–0.15) than the uptake at the forest (–0.045) and clear-felled sites (0.0027). Although there were no significant differences among the sites, N₂O emission (kg N ha^?1 per 4 months) was slightly lower at the burnt site (0.013) and higher at the clear-felled site (0.068) than at the forest site (0.038). This different influence of burning and tree felling on CH₄ and N₂O fluxes might result from changes in the physical and chemical properties of the soil with respect to forest fire.     

Emission of CO2 from the surface of oligotrophic bogs with due account for their microrelief in the southern taiga of European Russia

The results of studying the carbon dioxide fluxes from the soil’s surface during three years taking into account the microrelief are summarized. More precise estimates were obtained for the annual CO₂ emission from the oligotrophic peat bogs differing in vegetation and waterlogging in the southern taiga of European Russia. The maximum differences in the rates of the CO₂ emission related to the microrelief elements are characteristic of the treeless ridge-pool complex, where the hollows (without vegetation) emitted CO₂ twice less than the flat areas and thrice less than the hummocks. In the forest bogs, the differences related to the microrelief were significantly lower. In the areas with the ridge-pool microrelief, the weighted average (for 3 years) CO₂ emission was 436 g C/m² per year; in the better drained natural dwarf shrub-cotton grass-sphagnum pine forest, 930; and in the drained pine forest, 1292 g C/m² per year. The share of the CO₂ amount emitted in the cold period (November–April) amounted to 10% of its annual flux from the peat soils of the ridge-pool complex and 17 and 24%, respectively, in the natural and drained pine forests.     

Carbon dioxide emissions of soils under pure and mixed stands of beech and spruce, affected by decomposing foliage litter mixtures

Soil respiration is the largest terrestrial source of CO₂ to the atmosphere. In forests, roughly half of the soil respiration is autotrophic (mainly root respiration) while the remainder is heterotrophic, originating from decomposition of soil organic matter. Decomposition is an important process for cycling of nutrients in forest ecosystems. Hence, tree species induced changes may have a great impact on atmospheric CO₂ concentrations. Since studies on the combined effects of beech-spruce mixtures are very rare, we firstly measured CO₂ emission rates in three adjacent stands of pure spruce (Picea abies), mixed spruce-beech and pure beech (Fagus sylvatica) on three base-rich sites (Flysch) and three base-poor sites (Molasse; yielding a total of 18 stands) during two summer periods using the closed chamber method. CO₂ emissions were higher on the well-aerated sandy soils on Molasse than on the clayey soils on Flysch, characterized by frequent water logging. Mean CO₂ effluxes increased from spruce (41) over the mixed (55) to the beech (59) stands on Molasse, while tree species effects were lower on Flysch (30-35, mixed > beech = spruce; all data in mg CO₂-C m⁻² h⁻¹). Secondly, we studied decomposition after fourfold litter manipulations at the 6 mixed species stands: the O_i - and O_e horizons were removed and replaced by additions of beech -, spruce - and mixed litter of the adjacent pure stands of known chemical quality and one zero addition (blank) in open rings (20 cm inner diameter), which were covered with meshes to exclude fresh litter fall. Mass loss within two years amounted to 61-68% on Flysch and 36-44% on Molasse, indicating non-additive mixed species effects (mixed litter showed highest mass loss). However, base cation release showed a linear response, increasing from the spruce - over the mixed - to the beech litter. The differences in N release (immobilization) resulted in a characteristic converging trend in C/N ratios for all litter compositions on both bedrocks during decomposition. In the summers 2006 and 2007 we measured CO₂ efflux from these manipulated areas (a closed chamber fits exactly over such a ring) as field indicator of the microbial activity. Net fluxes (subtracting the so-called blank values) are considered an indicator of litter induced changes only and increased on both bedrocks from the spruce - over the mixed - to the beech litter. According to these measurements, decomposing litter contributed between 22-32% (Flysch) and 11-28% (Molasse) to total soil respiration, strengthening its role within the global carbon cycle.     

The Effect of Contrasting Moistening Regimes on CO<Subscript>2</Subscript> Emission from the Gray Forest Soil under a Grass Vegetation and Bare Fallow

The effect of contrasting moisture regimes on the CO₂ emission from the gray forest soils (Haplic Luvisols (Loamic, Cutanic, Humic)) under a grass vegetation and bare fallow was studied in a field simulation experiment in June–September, 2015 (Moscow region). Two short soil droughts (53 and 34 days) and a long one (94 days) were simulated on plots isolated from precipitation. A variant with regular irrigation, where the soil moisture was maintained 60–70% of their water holding capacity, was used as a control. Over the whole observation period, the CO₂ emissions from the soils studied decreased by a factor of 1.8 compared to the control only in the variant with the grass vegetation under prolonged drought. During the first hours after irrigation of the dry plots, the soil respiration intensified due to the “Birch effect”. The magnitude of this effect was 84–104% in the soils under the grass vegetation and 114–133% in the fallow areas. Owing to this phenomenon, the total CO₂ emission from the soils subjected to two short droughts was equal to the CO₂ flux under regular moistening for the grass plots and exceeded it by almost 1.3 times for the fallow plots as compared to the control. However, the share of extra CO₂ flux induced by moistening of the dry soils did not exceed 8–10% of the total CO₂ emission over the whole observation period.     

Variability of CO2 and N2O emissions during freeze‐thaw cycles: results of model experiments on undisturbed forest‐soil cores

The amounts of N₂O released in periods of alternate freezing and thawing depend on site and freezing conditions, and contribute considerably to the annual N₂O emissions. However, quantitative information on the N₂O emission level of forest soils in freeze‐thaw cycles is scarce, especially with regard to the direct and indirect effect of tree species and the duration of freezing. Our objectives were (i) to quantify the CO₂ and N₂O emissions of three soils under beech which differed in their texture, C and N contents, and humus types in freeze‐thaw cycles, and (ii) to study the effects of the tree species (beech (Fagus sylvatica L.) and spruce (Picea abies (L.) Karst.)) for silty soils from two adjacent sites and the duration of freezing (three and eleven days) on the emissions. Soils were adjusted to a matric potential of –0.5 kPa, and emissions were measured in 3‐hr intervals for 33 days. CO₂ emissions of all soils were similar in the two freeze‐thaw cycles, and followed the temperature course. In contrast, the N₂O emissions during thawing differed considerably. Large N₂O emissions were found on the loamy soil under beech (Loam‐beech) with a maximum N₂O emission of 1200 μg N m^–2 h^–1 and a cumulative emission of 0.15 g N m^–2 in the two thawing periods. However, the sandy soil under beech (Sand‐beech) emitted only 1 mg N₂O‐N m^–2 in the two thawing periods probably because of a low water‐filled pore space of 44 %. The N₂O emissions of the silty soil under beech (Silt‐beech) were small (9 mg N m^–2 in the two thawing periods) with a maximum emission of 150 μg N m^–2 h^–1 while insignificant N₂O emissions were found on the silty soil under spruce (0.2 mg N m^–2 in the two thawing periods). The cumulative N₂O emissions of the short freeze‐thaw cycles were 17 % (Sand‐beech) or 22 % (Loam‐beech, Silt‐beech) less than those of the long freeze‐thaw cycles, but the differences between the emissions of the two periods were not significant (P ≤ 0.05). The results of the study show that the amounts of N₂O emitted in freeze‐thaw cycles vary markedly among different forest soils and that the tree species influence the N₂O thawing emissions in forests considerably due to direct and indirect impacts on soil physical and chemical properties, soil structure, and properties of the humus layer.     

Carbon Dioxide Flux in a Subtropical Agricultural Soil of China

Red soils, one of the typical agricultural soils in subtropical China, play important roles in the global carbon budget due to their large potential to sequester C and replenish atmospheric C through soil CO₂ flux. Soil CO₂ emission was measured using a closed chamber method to quantify year-round soil flux and to determine the contribution of soil temperature, dissolved organic carbon (DOC) and soil moisture content to soil CO₂ flux. Soil flux was determined every 10 d during the experiment from August 1999 to July 2000, at the Ecological Station of Red Soil (the Chinese Academy of Sciences). In addition, diurnal flux measurements for 24 hr were made on August 5 and November 5, 1999 during this experiment. The average soil fluxes from 2 hr measurements between 9:00 and 11:00 can be regarded as the representative of daily averages. Soil CO₂ fluxes were generally higher in summer and autumn than in winter and spring, averaged 7.16 and 0.86 g CO₂ m^-2 d^-1 for the former and latter two seasons, and had a seasonal pattern more similar to soil temperature and DOC than soil moisture. The annual soil CO₂ flux was estimated as 1.65 kg CO₂ m^-2 yr^-1. Regressed separately, the reasons for soil flux variability were 86.6% from soil temperature, 58.8% from DOC, and 26.3% from soil moisture, respectively. Regressed jointly, a multiple equation was developed by the above three variables that explained 85.2% of the flux variance, but only soil temperature was the dominant factor affectingsoil flux, with significant partial correlation coefficient (r² = 0.804, p ≤ 0.05), through stepwise regression analysis. Based on the exponential equation using soil temperature, the predicted fluxes were calculated and were essentially equal to the measured ones throughout the experiment. No significant difference was detected between the predicted average and the measured one. The exponential relationship describing the response of soil CO₂ flux to the changes in soil temperature should accurately predict soil CO₂ flux from red soils in subtropical China.     

Carbon dioxide fluxes following tillage from a mollisol in the Argentine Rolling Pampa

Carbon dioxide emission from soil plays an important role in the global carbon cycle. Short term losses of soil carbon due to tillage are of a variable magnitude. Our objective was to evaluate the effect of plowing the soil on CO₂-C emissions during summer in a coarse-loamy mixed thermic Typic Hapludoll from the Argentine Rolling Pampa. Temperature after tillage was higher in the plowed soil than under no-tillage, being higher the soil water content in the later treatment. Plowing the soil did not produce an immediately impact on soil surface CO₂-C emission, but induced an important CO₂-C flush few days later. A difference of 16 up to 25 kg C ha^–1 d^–1 in the CO₂-C emissions was observed from the second up to the fourth sampling dates after tillage. Difference in total CO₂-C emissions between the plowed soil and the no-tillage treatment was 580 kg C ha^–1, during the 40 days measurement period. This difference in CO₂-C emission was partitioned between residue decomposition and humus mineralization. Carbon mineralized from humus was 270 kg C ha^–1 higher under plow tillage than under no tillage. This figure represented an important extra loss of 0.48% of the soil organic carbon content from the 0–30 cm depth, as consequence of plowing in the warmest season of the year.     

Emission of CO2 by soils in the impact zone of the Severonikel smelter in the Kola subarctic region

The intensity of the in situ soil respiration in the background northern taiga spruce forests of the Kola subarctic region reaches 120–290 mg C-CO₂/m² per h. In the impact zone of the Severonikel smelter, it decreases to 90–140, 30, and 15–30 mg C-CO₂/m² per h at the stages of spruce defoliation, spruce-birch woodland, and technogenic barrens of the technogenic succession, respectively. For the first time, the impact of the industrial pollution on root respiration has been assessed, and the dependences of the CO₂ emission, the contribution of mineral soil horizons to this process, the microbial biomass, and root respiration on the concentrations of available nickel and copper compounds have been determined. The efficiency of two remediation technologies applied to technogenic barrens near the smelter has been evaluated on the basis of four parameters of the soil biological activity. The results indicate that remediation with the creation of a new filled soil layer is more efficient than chemical and phytoremediation methods.     

Interannual and interseasonal soil CO2 efflux and VOC exchange rates in a Mediterranean holm oak forest in response to experimental drought

Climate models predict drier conditions in the next decades in the Mediterranean basin. Given the importance of soil CO₂ efflux in the global carbon balance and the important role of soil monoterpene and volatile organic compounds (VOCs) in soil ecology, we aimed to study the effects of the predicted drought on soil CO₂, monoterpenes and other VOC exchange rates and their seasonal and interannual variations. We decreased soil water availability in a Mediterranean holm oak forest soil by means of an experimental drought system performed since 1999 to the present. Measurements of soil gas exchange were carried out with IRGA, GC and PTR-MS techniques during two annual campaigns of contrasting precipitation. Soil respiration was twice higher the wet year than the dry year (2.27±0.26 and 1.05±0.15, respectively), and varied seasonally from 3.76±0.85 μmol m⁻² s⁻¹ in spring, to 0.13±0.01 μmol m⁻² s⁻¹ in summer. These results highlight the strong interannual and interseasonal variation in CO₂ efflux in Mediterranean ecosystems. The drought treatment produced a significant soil respiration reduction in drought plots in the wet sampling period. This reduction was even higher in wet springs (43% average reduction). These results show (1) that soil moisture is the main factor driving seasonal and interannual variations in soil respiration and (2) that the response of soil respiration to increased temperature is constrained by soil moisture. The results also show an additional control of soil CO₂ efflux by physiology and phenology of trees and animals. Soil monoterpene exchange rates ranged from −0.01 to 0.004 nmol m⁻² s⁻¹, thus the contribution of this Mediterranean holm oak forest soil to the total monoterpenes atmospheric budget seems to be very low. Responses of individual monoterpenes and VOCs to the drought treatment were different depending on the compound. This suggests that the effect of soil moisture reduction in the monoterpenes and VOC exchange rates seems to be dependent on monoterpene and VOC type. In general, soil monoterpene and other VOC exchange rates were not correlated with soil CO₂ efflux. In all cases, only a low proportion of variance was explained by the soil moisture changes, since almost all VOCs increased their emission rates in summer 2005, probably due to the effect of high soil temperature. Results indicate thus that physical and biological processes in soil are controlling soil VOC exchange but further research is needed on how these factors interact to produce the observed VOCs exchange responses.     

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.     

Evaluation of organic carbon stocks and СО<Subscript>2</Subscript> fluxes in grasslands of Western Transbaikalia

The stocks of organic carbon and mean rates of the CO₂ emission during the growing season (May–September) and the entire year were estimated in a sequence of grass ecosystems along the transect encompassing chestnut and meadow-chestnut steppe soils, marsh and meadow alluvial soils, and a haloxerophytic community on a typical solonchak. The total stocks of organic carbon comprised 6.17–9.70 kg С/m² in steppe, 7.41–10.04 kg С/m² in floodplain, and 4.74 kg С/m² in haloxerophytic ecosystems. The portion of humus carbon in the upper 50-cm-thick soil layer comprised 79–92% of the total carbon stock. The mean daily CO₂ emission (С–CO₂/(m² day)) from alluvial soils was moderate (3.3–4.9) or low (1.5–2.5). The dependence of the CO₂ emission on the moistening of steppe soils, temperature of alluvial soils, and temperature and moistening of solonchak was revealed. In comparison with the CO₂ emission from the zonal chestnut soil, its mean values during the growing season and the entire year were 1.2 times higher for the meadowchestnut soil, 3.3 times higher for the marsh alluvial soil, 2.3 times higher for the meadow alluvial soil, and 1.7 times higher for the solonchak. The portion of the CO₂ emission beyond the growing season in the mean annual emission averaged 19.8–24.2% and depended on the type of grass ecosystem and on weather conditions of particular years. The sink of carbon in the grass ecosystems exceeded carbon emission, especially in the steppe ecosystems.     

The effect of boreal forest composition on soil respiration is mediated through variations in soil temperature and C quality

Getting a better understanding of CO₂ efflux from forest soils is critical for increasing our comprehension of the global C cycle. We examined the influence of two common boreal tree species, either in pure stands (BS = black spruce; TA = trembling aspen) or in mixtures (MW = BS + TA mixedwood), on total (R_S), heterotrophic (R_H) and autotrophic soil respiration (R_A) and their relationship with soil temperature and moisture, distance to the nearest tree, labile and total soil organic C (SOC), and root content. Stand-specific soil respiration–temperature models were developed to estimate annual soil CO₂ efflux. Soil temperature was the main factor explaining R_S and its components, followed by labile and total SOC. These three variables were significantly affected by forest composition, while no difference in soil moisture, distance to the nearest tree and root content was observed between stand types. A reciprocal forest floor transplant experiment showed that the influence of stand types on mineral soil temperature was due to a difference in light penetration rather than forest floor characteristics. Annual R_S and R_H were significantly greater in MW and TA than in BS, whereas annual R_A was greater in BS and MW than in TA. Temperature sensitivity (Q₁₀) of both R_S and R_H was significantly higher in BS than in MW and TA, suggesting that CO₂ efflux from BS soils could be increased more under climate warming than that from the other stand types. Our results show evidence that boreal forest composition affects soil CO₂ efflux and that litter quality is not the only factor explaining the differences between stand types. The influence of forest composition on soil CO₂ efflux would be mediated through effects on soil temperature as well as on factors affecting the accumulation and the quality of SOC.     

Evaluation of the soil carbon budget under different upland cropping systems in central Hokkaido,Japan

Abstract

To evaluate the carbon budget in soils under different cropping systems, the carbon dioxide (CO₂) flux from soils was measured in a total of 11 upland crop fields within a small watershed in central Hokkaido over the no snow cover months for 3 years. The CO₂ flux was measured using a closed chamber method at bare plots established in each field to estimate soil organic matter decomposition. Temporal variation in instantaneous soil CO₂ fluxes within the sites was mainly controlled by soil temperature and moisture. Annual mean CO₂ fluxes and cumulative CO₂ emissions had no significant relationship with soil temperature and moisture (P > 0.2). However, there was a significant quadratic relationship between annual mean CO₂ flux or cumulative CO₂ emission and soil clay plus silt content (%) (R² = 0.72～0.74, P < 0.0003). According to this relationship, the optimum condition for soil CO₂ emission is at a clay plus silt content of 63%. The cumulative CO₂ emission during the no snow cover season within each year varied from 1,159 to 7,349 kg C ha^?1 at the different sites. The amount of crop residue carbon retained in the soils following a cropping season was not enough to offset the CO₂ emission from soil organic matter decomposition at all sites. As a consequence, the calculation of the soil carbon budget (i.e. the difference between the carbon added as crop residues and compost and the carbon lost as CO₂ from organic matter decomposition) ranged from –7,349 to –785 kg C ha^?1, except for a wheat site where a positive value of 4,901 kg C ha^?1 was observed because of a large input of organic carbon with compost. The negative values of the soil carbon budget indicate that these cropping systems were net sources of atmospheric CO₂.