Hierarchical Bayesian models for soil CO2 flux using soil texture: a case study in central Hokkaido,Japan

Hierarchical Bayesian (HB) methods are useful tools for modeling multifaceted, nonlinear phenomena such as those encountered in ecology, and have been increasingly applied in environmental sciences, e.g., to estimate soil gas flux from different soil textures or sites. We have developed a model of soil carbon dioxide (CO₂) flux based on soil temperature (T, 5 cm depth) and water-filled pore space (WFPS, 5 cm depth) using HB theory. The HB model was calibrated using a dataset of CO₂ flux measured from bare soils belonging to four texture classes in 14 upland field sites in a watershed in central Hokkaido, Japan, in the nonsnow-cover season from 2003 to 2011. The numerical software HYDRUS-1D was used to simulate daily WFPS, and the estimated values were significantly correlated with the measured WFPS (R² = 0.68, P < 0.001). Compared to a nonhierarchical Bayesian model (Bayesian pooled model), the CO₂ predictions with the HB model more accurately represented texture-specific observations. The simulation–observation fit of the CO₂ flux model was R² = 0.64 (P < 0.001). More than 90% of the observed daily data were within the 95% confidence interval. The HB model exhibited high uncertainty for high CO₂ flux values. The HB model calibration revealed differing sensitivity of CO₂ flux to T and WFPS in different soil texture classes. CO₂ flux increased with an increase in T, and it increased to a lesser degree with a finer texture, possibly because the clay and silt facilitated soil aggregation, thus reducing temperature fluctuations. WFPS values between 0.48 and 0.64 resulted in optimal conditions for CO₂ flux. The minimum WFPS value increased with an increase in clay content (P < 0.05). Although only a small number of soil types were studied in only one season in this study, the HB model may provide a method for predicting how the effects of soil temperature and moisture on CO₂ flux change with texture, and soil texture could be regarded as an upscaling factor in future research on regional extrapolation.     

Soil CO2 flux in six monospecific forest plantations in Southern Rwanda

Forest soils contain the largest carbon stock of all terrestrial biomes and are probably the most important source of carbon dioxide (CO₂) to atmosphere. Soil CO₂ fluxes from 54 to 72-year-old monospecific stands in Rwanda were quantified from March 2006 to December 2007. The influences of soil temperature, soil water content, soil carbon (C) and nitrogen (N) stocks, soil pH, and stand characteristics on soil CO₂ flux were investigated. The mean annual soil CO₂ flux was highest under Eucalyptus saligna (3.92 μmol m⁻² s⁻¹) and lowest under Entandrophragma excelsum (3.13 μmol m⁻² s⁻¹). The seasonal variation in soil CO₂ flux from all stands followed the same trend and was highest in rainy seasons and lowest in dry seasons. Soil CO₂ flux was mainly correlated to soil water content (R² = 0.36-0.77), stand age (R² = 0.45), soil C stock (R² = 0.33), basal area (R² = 0.21), and soil temperature (R² = 0.06-0.17). The results contribute to the understanding of factors that influence soil CO₂ flux in monocultural plantations grown under the same microclimatic and soil conditions. The results can be used to construct models that predict soil CO₂ emissions in the tropics.     

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.     

CO2, CH4 and N2O fluxes of upland black spruce (Picea mariana) forest soils after forest fires of different intensity in interior Alaska

Abstract

Forest fires can change the greenhouse gase (GHG) flux of borea forest soils. We measured carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) fluxes with different burn histories in black spruce (Picea mariana) stands in interior Alaska. The control forest (CF) burned in 1920; partially burned (PB) in 1999; and severely burned (SB1 and SB2) in 2004. The thickness of the organic layer was 22 ± 6 cm at CF, 28 ± 10 cm at PB, 12 ± 6 cm at SB1 and 4 ± 2 cm at SB2. The mean soil temperature during CO₂ flux measurement was 8.9 ± 3.1, 6.4 ± 2.1, 5.9 ± 3.4 and 5.0 ± 2.4°C at SB2, SB1, PB and CF, respectively, and differed significantly among the sites (P < 0.01). The mean CO₂ flux was highest at PB (128 ± 85 mg CO₂-C m^?2 h^?1) and lowest at SB1 (47 ± 19 mg CO₂-C m^?2 h^?1) (P < 0.01), and within each site it was positively correlated with soil temperature (P < 0.01). The CO₂ flux at SB2 was lower than that at CF when the soil temperature was high. We attributed the low CO₂ flux at SB1 and SB2 to low root respiration and organic matter decomposition rates due to the 2004 fire. The CH₄ uptake rate was highest at SB1 [–91 ± 21 μg CH₄-C m^?2 h^?1] (P < 0.01) and positively correlated with soil temperature (P < 0.01) but not soil moisture. The CH₄ uptake rate increased with increasing soil temperature because methanotroph activity increased. The N₂O flux was highest [3.6 ± 4.7 μg N₂O-N m^?2 h^?1] at PB (P < 0.01). Our findings suggest that the soil temperature and moisture are important factors of GHG dynamics in forest soils with different fire history.     

Estimating NEE in a wheat-planted plot with an automatically controlled chamber

Abstract

We observed carbon dioxide (CO₂) flux at two experimental plots (wheat (Triticum aestivum L.) -planted and bare) for a year using an automatically controlled chamber. At each plot, two chambers were installed at six observation points by rotation. Consequently, the total installment duration at each point was one-third of the entire experimental period. Although we manually moved the chambers periodically, they hampered wheat growth and reduced the dried weight of harvested wheat by 65%. However, they did not influence the carbon (C) content ratio of harvested wheat. The rate of decrease of soil water contents after rainfall in the wheat plot was higher than that in the bare plot, especially after the canopy height reached around 30 cm. The maximum gap of soil water content at 5 cm depth between the two plots was about 5%. Wheat mitigated the increase of soil temperature in the daytime. The gap of soil temperature at 2 cm depth between the two plots sometimes exceeded 10°C. Considering the difference between dried weights of harvested wheat per unit ground area inside and outside the chamber collar, the annual net ecosystem exchange (NEE), whole ecosystem respiration and gross primary production were estimated respectively as –103 g C m^?2 y^?1, 831 g C m^?2 y^?1 and–934 g C m^?2 y^?1. The absolute values of each were smaller than those reported from past studies. Adding the exported carbon of harvested wheat (364 g C m^?2) and subtracting the imported carbon of the seeds (3.1 g C m^?2) to the NEE, net biome production across the ground surface was 259 g C m^?2. It was greater than that in the bare plot (187 g C m^?2). Although further improvements of measurements and more accurate estimated equations are necessary to evaluate the carbon budget correctly with chamber measurements, our chamber measurement captured the NEE variation, responding to seasonal, meteorological and biological changes.     

淡水湿地不同围垦土壤非耕季节呼吸速率差异

选择何种湿地利用方式,使得土壤固碳能力及CO₂气体排放受到的影响最小,是合理利用湿地、减少温室气体排放的关键所在,湿地土壤呼吸不仅受环境条件的影响,还受土壤本身性状的影响。以皖江地区为研究区域,利用定位试验对天然湿地及不同围垦利用方式下土壤在非耕季节CO₂排放通量、大气温度及表层土壤温度进行测定,并对其土壤TOC含量进行分析。结果表明,CO₂排放通量:水稻田[700.70 mg/(m²·h)]> 旱地[433.80 mg/(m²·h)]> 天然湿地[302.66 mg/(m²·h)],天然湿地土壤TOC含量明显高于围垦旱地及水稻田(0-30 cm),说明天然湿地较围垦旱地和水稻田对大气中CO₂浓度贡献最小,能存储更多的碳。探讨了CO₂排放通量与温度的相关性,得出3种土壤类型CO₂排放通量与大气温度和表层土壤温度均呈正相关关系。     

SOIL CO2 FLUX IN GRASSLAND,AFFORESTED LAND AND RECLAIMED COALMINE OVERBURDEN DUMPS: A CASE STUDY

The aim of this study was to measure the in situ soil CO₂ flux from grassland, afforested land and reclaimed coalmine overburden dumps by using the automated soil CO₂ flux system (LICOR‐8100® infrared gas analyzer, LICOR Inc., Lincoln, NE). The highest soil CO₂ flux was observed in natural grassland (11·16 µmol CO₂ m⁻²s⁻¹), whereas the flux was reduced by 38 and 59 per cent in mowed site and at 15‐cm depth, respectively. The flux from afforested area was found 5·70 µmol CO₂ m⁻²s⁻¹, which is 50 per cent lower than natural grassland. In the reclaimed coalmine overburden dumps, the average flux under tree plantation was found to be lowest in winter and summer (0·89–1·12 µmol CO₂ m⁻²s⁻¹) and highest during late monsoon (3–3·5 µmol CO₂ m⁻²s⁻¹). During late monsoon, the moisture content was found to be higher (6–7·5 per cent), which leads to higher microbial activity and decomposition. In the same area under grass cover, soil CO₂ flux was found to be higher (8·94 µmol CO₂ m⁻²s⁻¹) compared with tree plantation areas because of higher root respiration and microbial activity. The rate of CO₂ flux was found to be determined predominantly by soil moisture and soil temperature. Our study indicates that the forest ecosystem plays a crucial role in combating global warming than grassland; however, to reduce CO₂ flux from grassland, mowing is necessary. Copyright © 2012 John Wiley & Sons, Ltd.     

Soil carbon dioxide flux and rice photosynthesis

Measurement of CO₂ concentration in air at 25 em below and 100 em above the canopy of a good rice crop indicated that a severe CO₂ deficit occurred around the photosynthetic surface of crop when light intensity was high. Soil CO₂ flux as measured by the soda lime method in a closed system ranged from 3.9 to 5.7 g.m^-2. day^-1 under flooded conditions and from 6.0 to 8,6g.m^-2 .day^-1 under drained conditions. Cropped soil released more CO₂ than bare soil under both flooded and drained conditions. The estimated contribution of soil CO₂ to gross photosynthesis was 6%, for the flooded soil and 7% for the drained soil or a contribution of 9 and 12% to net dry matter production. These results together with other information indicate that atmospheric CO₂ is the most important source of CO₂, in crop photosynthesis, soil CO₂ released into atmosphere Is second most important, and soil CO₂ absorbed by plant roots is almost negligible.     

Mulching Affects Soil Properties and Greenhouse Gas Emissions Under Long‐Term No‐Till and Plough‐Till Systems in Alfisol of Central Ohio

Agricultural activities emit greenhouse gases (GHGs) and contribute to global warming. Intensive plough tillage (PT), use of agricultural chemicals and the burning of crop residues are major farm activities emitting GHGs. Intensive PT also degrades soil properties by reducing soil organic carbon (SOC) pool. In this scenario, adoption of no‐till (NT) systems offers a pragmatic option to improve soil properties and reduce GHG emission. We evaluated the impacts of tillage systems (NT and PT) and wheat residue mulch on soil properties and GHG emission. This experiment was started in 1989 on a Crosby silt loam soil at Waterman Farm, The Ohio State University, Columbus, Ohio, USA. Mulching reduced soil bulk density and improved total soil porosity. More total carbon (16.16 g kg⁻¹), SOC (8.36 mg L⁻¹) and soil microbial biomass carbon (152 µg g⁻¹) were recorded in soil under NT than PT. Mulch application also decreased soil temperature (0–5 cm) and penetration resistance (0–60 cm). Adoption of long‐term NT reduced the GHG emission. Average fluxes of GHGs under NT were 1.84 g CO₂‐C m⁻² day⁻¹ for carbon dioxide, 0.07 mg CH₄‐C m⁻² day⁻¹ for methane and 0.73 mg N₂O‐N m⁻² day⁻¹ for nitrous oxide compared with 2.05 g CO₂‐C m⁻² day⁻¹, 0.74 mg CH₄‐C m⁻² day⁻¹ and 1.41 mg N₂O‐N m⁻² day⁻¹, respectively, for PT. Emission of nitrous oxide was substantially increased by mulch application. In conclusion, long‐term NT reduced the GHG emission by improving the soil properties. Copyright © 2016 John Wiley & Sons, Ltd.     

Carbon Dioxide Emission from Black Soil as Influenced by Land‐Use Change and Long‐Term Fertilization

Land‐use change and soil management play a vital role in influencing losses of soil carbon (C) by respiration. The aim of this experiment was to examine the impact of natural vegetation restoration and long‐term fertilization on the seasonal pattern of soil respiration and cumulative carbon dioxide (CO₂) emission from a black soil of northeast China. Soil respiration rate fluctuated greatly during the growing season in grassland (GL), ranging from 278 to 1030 mg CO₂ m^?2 h^?1 with an average of 606 mg CO₂ m^?2 h^?1. By contrast, soil CO₂ emission did not change in bareland (BL) as much as in GL. For cropland (CL), including three treatments [CK (no fertilizer application), nitrogen, phosphorus and potassium application (NPK), and NPK together with organic manure (OM)], soil CO₂ emission gradually increased with the growth of maize after seedling with an increasing order of CK < NPM < OM, reaching a maximum on 17 August and declining thereafter. A highly significant exponential correlation was observed between soil temperature and soil CO₂ emission for GL during the late growing season (from 3 August to 28 September) with Q₁₀ = 2.46, which accounted for approximately 75% of emission variability. However, no correlation was found between the two parameters for BL and CL. Seasonal CO₂ emission from rhizosphere soil changed in line with the overall soil respiration, which averaged 184, 407, and 584 mg CO₂ m^?2 h^?1, with peaks at 614, 1260, and 1770 mg CO₂ m^?2 h^?1 for CK, NPK, and OM, respectively. SOM‐derived CO₂ emission of root free‐soil, including basal soil respiration and plant residue–derived microbial decomposition, averaged 132, 132, and 136 mg CO₂ m^?2 h^?1, respectively, showing no difference for the three CL treatments. Cumulative soil CO₂ emissions decreased in the order OM > GL > NPK > CK > BL. The cumulative rhizosphere‐derived CO₂ emissions during the growing season of maize in cropland accounted for about 67, 74, and 80% of the overall CO₂ emissions for CK, NPK, and OM, respectively. Cumulative CO₂ emissions were found to significantly correlate with SOC stocks (r = 0.92, n = 5, P < 0.05) as well as with SOC concentration (r = 0.97, n = 5, P < 0.01). We concluded that natural vegetation restoration and long‐term application of organic manure substantially increased C sequestration into soil rather than C losses for the black soil. These results are of great significance to properly manage black soil as a large C pool in northeast China.     

Calibrating soil respiration measures with a dynamic flux apparatus using artificial soil media of varying porosity

Measurement of soil respiration to quantify ecosystem carbon cycling requires absolute, not relative, estimates of soil CO₂ efflux. We describe a novel, automated efflux apparatus that can be used to test the accuracy of chamber‐based soil respiration measurements by generating known CO₂ fluxes. Artificial soil is supported above an air‐filled footspace wherein the CO₂ concentration is manipulated by mass flow controllers. The footspace is not pressurized so that the diffusion gradient between it and the air at the soil surface drives CO₂ efflux. Chamber designs or measurement techniques can be affected by soil air volume, hence properties of the soil medium are critical. We characterized and utilized three artificial soils with diffusion coefficients ranging from 2.7 × 10^?7 to 11.9 × 10^?7 m² s^?1 and porosities of 0.26 to 0.46. Soil CO₂ efflux rates were measured using a commercial dynamic closed‐chamber system (Li‐Cor 6400 photosynthesis system equipped with a 6400‐09 soil CO₂ flux chamber). On the least porous soil, small underestimates (< 5%) of CO₂ effluxes were observed, which increased as soil diffusivity and soil porosity increased, leading to underestimates as high as 25%. Differential measurement bias across media types illustrates the need for testing systems on several types of soil media.     

Soil respiration in a tropical grassland

Soil respiration throughout an annual cycle was measured at three different stands in a tropical grassland situated at Kurukshetra at 29°58' N lat. and 76°51' E long. Rates of CO₂ evolution were measured by alkali absorption using 13 cm dia × 23 cm aluminium cylinders inserted 10 cm into the ground. Both movable and permanently-fixed cylinders were used. The CO₂ evolution rates for the three stands were: Stand I (dominated by Sesbania bispinosa) 49–358 mg CO₂ m^?2 h^?1; Stand II (mixed grasses) 55–378 mg CO₂m^?2 h^?1; and Stand III (dominated by Desmostachya bipinnata) 55–448 mg CO₂ m^?2 h^?1. A positive significant relation existed between rate of CO₂ evolution and soil water content (r = 0.59?0.740), and between soil respiration and temperature (r = 0.58?0.69). A statistical model developed on the basis of the relationship between CO₂ evolution rates and certain abiotic environmental factors showed 69% comparability between the calculated and observed values of soil respiration. The contribution of root and root-associated microorganisms to total soil respiration was estimated at 42% using the relationship between root biomass and CO₂ output from movable cylinders.     

Soil carbon dioxide fluxes in established switchgrass land managed for biomass production

Switchgrass (Panicum virgatum L.) grown for biomass feedstock production has the potential to increase soil C sequestration, and soil CO₂ flux in grassland is an important component in the global C budget. The objectives of this study were to: (1) determine the effects of N fertilization and harvest frequency on soil CO₂ flux, soil microbial biomass carbon (SMBC), and potentially mineralizable carbon (PMC); and (2) evaluate the relationship of soil CO₂ flux with soil temperature, soil moisture, SMBC, and PMC. Two N rates (0 and 224 kg ha⁻¹) were applied as NH₄NO₃ and cattle (Bos Taurus L.) manure. Switchgrass was harvested every year at anthesis or alternate years at anthesis. The data were collected during growing season (May-October) 2001-2004 on switchgrass-dominated Conservation Reserve Program (CRP) land in east-central South Dakota, USA. Manure application increased soil CO₂ flux, SMBC, and PMC during the early portion of the growing season compared with the control, but NH₄NO₃ application did not affect soil CO₂ flux, SMBC, and PMC. However, seasonal variability of soil CO₂ flux was not related to SMBC and PMC. Estimated average soil CO₂ fluxes during the growing periods were 472, 488, and 706 g CO₂-C m⁻² for control, NH₄NO₃-N, and manure-N plots, respectively. Switchgrass land with manure application emitted more CO₂, and approximately 45% of the C added with manure was respired to the atmosphere. Switchgrass harvested at anthesis decreased soil CO₂ flux during the latter part of the growing season, and flux was lower under every year harvest treatment than under alternate years harvest. Soil temperature was the most significant single variable to explain the variability in soil CO₂ flux. Soil water content was not a limiting factor in controlling seasonal CO₂ flux.     

黑土不同土地利用方式下受水分有效性调节的土壤CO2排放的温度敏感性

The quantification of soil CO2 efflux is crucial for better understanding the interactions between driving variables and C losses from black soils in Northeast China and for assessing the function of black soil as a net source or sink of atmospheric CO2 depending upon land use.This study investigated responses of soil CO2 efflux variability to soil temperature interactions with diferent soil moisture levels under various land use types including grassland,bare land,and arable(maize,soybean,and wheat)land in the black soil zone of Northeast China.The soil CO2 effluxes with and without live roots,defined as the total CO2 efflux(FtS)and the root-free CO2 efflux(FrfS),respectively,were measured from April 2009 to May 2010 using a static closed chamber technique with gas chromatography.The seasonal soil CO2 fluxes tended to increase from the beginning of the measurements until they peaked in summer and then declined afterwards.The mean seasonal FtS ranged from 20.3±7.8 to 58.1±21.3 mg CO2-C m-2h-1 for all land use types and decreased in the order of soybean land>grassland>maize land>wheat land>bare land,while the corresponding values of FrfS were relatively lower,ranging from 20.3±7.8 to 42.3±21.3 mg CO2-C m-2h-1.The annual cumulative FtS was in the range of 107-315 g CO2-C m-2 across all land uses types.The seasonal CO2 effluxes were significantly(P<0.001)sensitive to soil temperature at 10 cm depth and were responsible for up to 62% of the CO2 efflux variability.Correspondingly,the temperature coefcient Q10 values varied from 2.1 to 4.5 for the seasonal FtS and 2.2 to 3.9 for the FrfS during the growing season.Soil temperature interacting with soil moisture accounted for a significant fraction of the CO2 flux variability for FtS (up to 61%) and FrfS (up to 67%) via a well-defined multiple regression model,indicating that temperature sensitivity of CO2 flux can be mediated by water availability,especially under water stress.     

Soil respiration of karst grasslands subjected to woody‐plant encroachment

The transition of grasslands to forests influences many ecosystem processes, including water and temperature regimes and the cycling of nutrients. Different components of the carbon biogeochemical cycle respond strongly to woody plant encroachment; as a consequence, the carbon balance of the invaded grasslands can change markedly. In our research, we studied the response of soil respiration (R_S) to natural succession of calcareous grassland. We established two research sites, called grassland and invaded site, at each of which eddy flux measurement were also performed. Within these sites, triplicate plots were fenced for soil flux measurements. At the invaded site, measurements were performed for forest patches and grassy spaces separately. Soil respiration was strongly dependent on temperature and reached 8–12 µmol CO₂ m^?2 s^?1 in mid‐summer; it was greater at the grassland than at the invaded site. R_S dependence on temperature and soil water content was similar between the different vegetation covers (grassland, gaps and forest patches). At a reference temperature of 10°C, the average R_S was 2.71 µmol CO₂ m^?2 s^?1. The annual sums of R_S were also similar between years and sites: 1345 ± 47 (2009) and 1150 ± 37 g C m^?2 year^?1 (2010) for grassland and 1324 ± 26 (2009) and 1268 ± 26 g C m^?2 year^?1 (2010) for the invaded site, which is at the upper range of the values reported in the literature. Cumulative R_S peaked in July, with about 200 g C m^?2. Large mid‐summer R_S rates rely on strong biological activity supported by high, but non‐extreme soil temperatures and by regular summer precipitation. A coupling of photosynthesis and R_S was revealed by a 24‐hour measurement, which showed asymmetrical clockwise hysteresis patterns.     

The effect of nitrogen fertilization and no‐till duration on soil nitrogen supply power and post–spring thaw greenhouse‐gas emissions

With a world population now > 7 billion, it is imperative to conserve the arable land base, which is increasingly being leveraged by global demands for producing food, feed, fiber, fuel, and facilities (i.e., infra‐structure needs). The objective of this study was to determine the effect of varying fertilizer‐N rates on soil N availability, mineralization, and CO₂ and N₂O emissions of soils collected at adjacent locations with contrasting management histories: native prairie, short‐term (10 y), and long‐term (32 y) no‐till continuous‐cropping systems receiving five fertilizer‐N rates (0, 30, 60, 90, and 120 kg N ha^–1) for the previous 9 y on the same plots. Intact soil cores were collected from each site after snowmelt, maintained at field capacity, and incubated at 20°C for 6 weeks. Weekly assessments of soil nutrient availability along with CO₂ and N₂O emissions were completed. There was no difference in cumulative soil N supply between the unfertilized long‐term no‐till and native prairie soils, while annual fertilizer‐N additions of 120 kg N ha^–1 were required to restore the N‐supplying power of the short‐term no‐till soil to that of the undisturbed native prairie soil. The estimated cumulative CO₂‐C and N₂O‐N emissions among soils ranged from 231.8–474.7 g m^–2 to 183.9–862.5 mg m^–2, respectively. Highest CO₂ fluxes from the native prairie soil are consistent with its high organic matter content, elevated microbial activity, and contributions from root respiration. Repeated applications of ≥ 60 kg N ha^–1 resulted in greater residual inorganic‐N levels in the long‐term no‐till soil, which supported larger N₂O fluxes compared to the unfertilized control. The native prairie soil N₂O emissions were equal to those from both short‐ and long‐term no‐till soils receiving repeated fertilizer‐N applications at typical agronomic rates (e.g., 90 kg N ha^–1). Eighty‐eight percent of the native soil N₂O flux was emitted during the first 2 weeks and is probably characteristic of rapid denitrification rates during the dormant vegetative period after snowmelt within temperate native grasslands. There was a strong correlation (R² 0.64; p < 0.03) between measured soil Fe‐supply rate and N₂O flux, presumably due to anoxic microsites within soil aggregates resulting from increased microbial activity. The use of modern no‐till continuous diversified cropping systems, along with application of fertilizer N, enhances the soil N‐supplying power over the long‐term through the build‐up of mineralizable N and appears to be an effective management strategy for improving degraded soils, thus enhancing the productive capacity of agricultural ecosystems. However, accounting for N₂O emissions concomitant with repeated fertilizer‐N applications is imperative for properly assessing the net global warming potential of any land‐management system.     

Long‐term effects of vehicular passages on soil carbon sequestration and carbon dioxide emission in a no‐till corn‐soybean rotation on a Crosby silt loam in Central Ohio,USA

Research information from a systematic planned study on the effects of vehicular passages and axle load on soil carbon dioxide (CO₂) fluxes and soil carbon (C) sequestration under long‐term NT farming is scanty. Therefore, the present study was conducted on an on‐going 20‐year experiment to assess the impacts of variable vehicular passages of a low axle load on soil CO₂ emission and soil C sequestration from a no‐till (NT) managed corn (Zea mays L.)–soybean (Glycine max Linneo) rotation in comparison with that a soil under woodlots (soils under natural wooded plantation). The experimental treatment consisted of an empty wagon [0 Mg load for compaction (C‐0; control)] compared with 2 (C‐2) and 4 (C‐4) passages of 2.5 Mg water wagon axle load, applied to the entire plot every year during April/May for 20 consecutive years. Soil samples were obtained in November 2016 to determine the effects of various vehicular passages on C and nitrogen (N) contents and CO₂ emissions. Soil CO₂ fluxes were measured from November 16, 2016, to May 30, 2017, on the bi‐weekly (November to December and April to May) and monthly (January to March) basis by using high‐density polyvinyl chloride static gas chambers. The soil CO₂ fluxes ranged from –1.05 to 9.03 g CO₂ m^?2 d^?1. The lowest soil CO₂ fluxes were observed in December coinciding with the minimum soil temperature. In general, daily soil CO₂ fluxes were higher under C‐0 than those under other treatments. Vehicular traffic and axle load reduced the cumulative emission of CO₂ by 22.6 and 29.8% under C‐2 and C‐4, respectively, compared with that under C‐0 (6.09 Mg ha^?1). Soil and air temperatures had a significant positive correlation with the diurnal fluxes of soil CO₂ in all the treatments except that under C‐4. Electrical conductivity, soil C and N contents and pools did not differ significantly among the treatments. Further, 2 to 4 passages of vehicles with 2.5 Mg of axle load decreased the soil CO₂ emission on Crosby silt loam under NT as compared to that under the control. Therefore, continuous cultivation of row crops with moderate trafficking under NT and residue retention is recommended, and it also reduces the potential of soil CO₂ emission while improving the soil organic C pools of well‐drained soils of Central Ohio.     

库布齐沙漠植被恢复对风沙土壤碳通量与碳储量的影响

为阐明库布齐沙漠植被恢复过程中土壤碳通量的时空动态特征及主控因子，明确土壤有机碳含量和储量的变化趋势，本研究以流动沙地、半固定沙地、藻结皮固定沙地和地衣苔藓混合结皮固定沙地为研究对象，运用静态暗箱–气相色谱法对风沙土壤碳通量及水热因子进行观测，并对土壤有机碳含量和密度进行测定和计算。结果表明，生长季内风沙土壤碳通量变异较大，季节动态与土壤温度基本一致，且随植被恢复碳通量呈递增趋势：混合结皮固定沙地(210.28 mg/(m~2·h))>藻结皮固定沙地(177.45 mg/(m~2·h))>半固定沙地(117.34 mg/(m~2·h))>流动沙地(65.61mg/(m~2·h))；土壤碳通量与各层土壤温度均显著正相关，除流动沙地土壤碳通量与深层土壤含水量显著负相关外，其余样地碳通量均与表层土壤含水量显著负相关；风沙土壤有机碳含量和密度随植被恢复而递增：混合结皮固定沙地(1.32 g/kg,0.94 kg/m~2)>藻结皮固定沙地(1.03 g/kg,0.74 kg/m~2)>半固定沙地(0.45 g/kg,0.36 kg/m~2)>流动沙地(0.27...     

Differences in soil CO2 flux between different land use types in mid-subtropical China

It is crucial to advance the understanding of the soil carbon dioxide (CO₂) flux and environmental factors for a better comprehension of carbon dynamics in subtropical ecosystems. Red soil, one of the typical agricultural soils in subtropical China, plays important roles in the global carbon budget due to their large potential to sequester C and replenish atmospheric C through soil CO₂ flux. We examined the relationship between soil CO₂ flux and environmental determinants in four different land use types of subtropical red soil-paddy (P), orchard (O), woodland (W) and upland (U) using static closed chamber method. Objectives were to evaluate the relationship of soil temperature, water-filled pore space (WFPS), and dissolved organic carbon (DOC) with the soil CO₂ flux. Soil CO₂ fluxes were measured on each site about every 14 days between 09:00 and 11:00 a.m. during 14-July 2004 to 25-April 2007 at the experimental station of Heshengqiao at Xianning, Hubei, China. Soil CO₂ fluxes revealed seasonal fluctuations, with the tendency that maximum values occurred in summer, minimum in winter and intermediate values in spring and autumn except for paddy soil when it was submerged. Further, significant differences in soil CO₂ fluxes were observed among the four soils, following the order of P > O > U  W. Average soil CO₂ fluxes were estimated as 901 ± 114, 727 ± 55, 554 ± 22 and 533 ± 27 (±S.D.) g CO₂ m⁻² year⁻¹ in paddy, orchard, upland and woodland soils, respectively. Variations in soil CO₂ flux were related to soil temperature, WFPS, and dissolved organic carbon with a combined R² of 0.49–0.75. Soil temperature was an important variable controlling 26–59% of soil CO₂ flux variability. The interaction of soil temperature and WFPS could explain 31–60% of soil CO₂ flux variations for all the land use types. We conclude that soil CO₂ flux from red soil is under environmental controls, soil temperature being the main variable, which interact with WFPS and DOC to control the supply of readily mineralizable substrates.     

亚热带气候环境条件下不同森林类型的土壤CO2通量的研究

The flux of carbon dioxide(CO2) from soil surface presents an important component of carbon(C) cycle in terrestrial ecosystems and is controlled by a number of biotic and abiotic factors. In order to better understand characteristics of soil CO2 flux(FCO2) in subtropical forests,soil FCO2 rates were quantified in five adjacent forest types(camphor tree forest,Masson pine forest,mixed camphor tree and Masson pine forest,Chinese sweet gum forest,and slash pine forest) at the Tianjiling National Park in Changsha,Hunan Province,in subtropical China,from January to December 2010. The influences of soil temperature(Tsoil),volumetric soil water content(θsoil),soil pH,soil organic carbon(SOC) and soil C/nitrogen(N) ratio on soil FCO2 rates were also investigated. The annual mean soil FCO2 rate varied with the forest types. The soil FCO2 rate was the highest in the camphor tree forest(3.53 ± 0.51 μmol m-2s-1),followed by,in order,the mixed,Masson pine,Chinese sweet gum,and slash pine forests(1.53 ± 0.25 μmol m-2 s1). Soil FCO2 rates from the five forest types followed a similar seasonal pattern with the maximum values occurring in summer(July and August) and the minimum values during winter(December and January). Soil FCO2 rates were correlated to Tsoiland θsoil,but the relationships were only significant for Tsoil. No correlations were found between soil FCO2 rates and other selected soil properties,such as soil pH,SOC,and C/N ratio,in the examined forest types. Our results indicated that soil FCO2 rates were much higher in the evergreen broadleaved forest than coniferous forest under the same microclimatic environment in the study region.