Soil N2O Fluxes Research Articles

Soil greenhouse gas emissions under enhanced efficiency and urea nitrogen fertilizer from Australian irrigated aerobic rice production

AbstractAerobic rice production offers a promising solution to improve water use efficiency and reduce methane (CH4) emissions by minimizing water inundation. However, alternate water‐saving methods for rice cultivation can lead to “trade‐off” emissions of nitrous oxide (N2O). A field experiment was conducted over one season measuring soil‐derived greenhouse gas emissions in irrigated aerobic rice (Oryza sativa L.) under different N fertilizer management at a rate of 220 kg N ha−1, including a nil treatment (“control”); slow release (180 days) polymer‐coated urea (“N180”); banded urea applied upfront (“urea”); and three applications of broadcast urea (“urea‐split”). The N180 treatment reduced soil N2O emissions compared with urea (p < 0.001), with mean cumulative N2O emissions of 4.36 ± 1.07 kg N ha−1 and 27.9 ± 5.70 kg N ha−1, respectively. Soil N2O fluxes were high, reaching up to 1916 and 2900 µg N m2 h−1 after urea application and irrigation/rain events, and were similar to other irrigated crops grown on heavy textured soils. Fertilizer N management had no effect on soil CH4 emissions, which were negligible across all treatments ranging from 1.28 to 2.75 kg C ha−1 over the growing season. Cumulative soil carbon dioxide emissions ranged from 1936 to 3071 kg C ha−1 and were greatest in N180. This case study provides the first evidence in Australia that enhanced efficiency nitrogen fertilizer can substantially reduce N2O emissions from soils in an aerobic rice system. Our findings reinforce the CH4 mitigation potential of water saving rice approaches and demonstrate the need to consider N fertilizer management to control N2O emissions.

Strip clear-cutting transformations increase soil N2O emissions in abandoned Moso bamboo forests

Forest transformation can markedly impact soil greenhouse gas emissions and soil environmental factors. Due to increasing labor costs and declining bamboo prices, the abandonment of Moso bamboo forests is sharply escalating in recent years, which weakens the carbon sequestration capacity and decreases the ecological function of forests. To improve the ecological quality of abandoned Moso bamboo forests, transformations of abandoned bamboo forests have occurred. However, the impact of such transformations on N2O emissions remains elusive. To bridge the knowledge gap, we conducted a 23-month field experiment to compare the effects of various forest management practices on soil N2O emissions and soil environmental factors in abandoned Moso bamboo forests in subtropical China. These practices included uncut abandonment as a control, intensive management, three intensities (light, moderate, and heavy) of strip clear-cutting with replanting local tree species, and clear-cutting with replanting transformation. During the experimental period, the mean soil N2O flux in abandoned Moso bamboo forests was 13.2 ± 0.1 μg m-2 h-1, representing a 44% reduction compared to intensive management forests. In comparison to the uncut control, light, moderate, and heavy strip clear-cutting and clear-cutting transformations increased soil N2O emission rates by 20%, 43%, 64%, and 94%, respectively. Soil temperature (69-71%), labile C (2-6%) and N (3-8%) were the main factors that explain N2O emissions following the transformation of abandoned Moso bamboo forests. Additionally, replanting could decrease soil N2O emissions by increasing the contribution of soil moisture. Overall, the light strip clear-cutting transformation is suggested to convert abandoned Moso bamboo forests to mitigate N2O emissions.

Water Conservation Practices and Nitrogen Fertility for the Reduction of Greenhouse Gas Emissions from Creeping Bentgrass Putting Greens

Irrigation practices that conserve water use have the potential to reduce greenhouse gas (GHG) emissions but may adversely affect turfgrass appearance. The purpose of this study was to identify irrigation practices and N fertilizers that will decrease carbon dioxide (CO2), methane (CH4,), and nitrous oxide (N2O) emissions while evaluating turfgrass color and quality. In both years, supplemental rainfall (SRF) soil moisture content was higher than business as usual (BAU) irrigation and syringing (SYR). Higher soil moisture led to increased fluxes in both soil CO2 and soil N2O. In 2017, the SRF fluxed lower soil CO2 as soil moisture reached levels that restricted respiration. Soil moisture was also an important predictor of soil N2O flux with BAU and SRF having higher soil N2O fluxes. SRF produced the greenest turf from May to July, whereas SRY and SRF produced the greenest turf from August to October in 2016. Both BAU and SRF had the greenest turf in 2017. BAU had the highest turfgrass quality ratings in 2016 followed by SRF and SRY, respectively, whereas in 2017 SRF and SRY had higher turfgrass quality ratings. When adopting water conservation practices to reduce GHG emissions, soil moisture content and site-specific rainfall should be closely monitored to prevent overwatering.

Reducing nitrogen fertilizer applications mitigates N2O emissions and maintains sugarcane yields in South China

Fertilizer N application combined with crop residue retention and a warm and humid climate increases nitrous oxide (N2O) emissions from sugarcane systems. However, the effects of high fertilizer N application rates on N2O emissions from sugarcane fields in China and the N2O reduction potential are still unclear. This study measured N2O emissions, the δ15N values for N2O and soil mineral N (NH4+ and NO3–), and yields during three continuous growing seasons in a sugarcane field in subtropical South China when four fertilizer N application rates: 0 (N0), 300 (N300), 400 (N400), and the local conventional rate of 500 kg N ha–1 (N500), were applied. The results showed that N2O emissions peaked in the first 4 weeks after fertilizer N application and the peak amplitude was highest after applying the N500 rate. The greatest soil N2O fluxes occurred when soil NH4+ and NO3– contents were high, the soil pore spaces contained large amounts of water (around 60 %), and there was a high soil surface temperature (around 35°C). The cumulative N2O emissions over the whole season (1.3–64.8 kg N ha–1) and emission factor values (2.6–11.1 %) both strongly increased with fertilizer N rate. The δ15N values for N2O and soil NH4+ and NO3– indicated that N2O production after N fertilization was dominated by denitrification and the microbial types varied with time and N fertilization rate. The principal component analysis showed that the factors associated with denitrification and nitrification explained 53.53 % and 30.53 % of the variation in N2O fluxes, respectively. Sugarcane yields, N uptake, and sugar contents were not affected by the reduced fertilizer N rates (N400 and N300) compared to that of N500. A reasonable N fertilizer rate of around 340 kg N ha–1 could reduce N2O emissions by more than 65 % compared to the conventional N500 rates while maintaining sugarcane yields. This study quantified the N2O emissions induced by different fertilizer N rates in a sugarcane system in China and highlighted the considerable potential for reducing N2O emissions through optimization of the fertilizer N application rate.

Modulation of soil nitrous oxide emissions and nitrogen leaching by hillslope hydrological processes

Soil nitrous oxide (N2O) emissions and nitrogen (N) leaching are key pathways for soil N loss in hillslope ecosystem, with potential implications for global warming and water body eutrophication. While soil N loss in hillslope ecosystem has been extensively studied, there is limited understanding of the spatiotemporal distribution patterns and factors driving soil N2O emissions and N leaching from a hillslope hydrology perspective. This study investigated N concentrations in leachate and soil N2O fluxes and their responses to soil hydrological factors on a tea plantation (TP) hillslope and a bamboo forest (BF) hillslope. Four distinct precipitation patterns—spring rainfall (SR), plum rain (PR), summer flood rain (SF), and drought period (DR)—were identified based on precipitation intensity, duration, and cumulative precipitation. Results showed that, soil N2O flux and leachate N concentrations were 8.2 times and 18.0 times higher On TP hillslope compared to the BF hillslope. The greatest soil N2O fluxes occurred during the PR period, while the lowest were observed during the DR period. Precipitation increased soil water content (SWC) and water-filled pore space, stimulating soil N cycling for N2O production. Fertilization activities and precipitation led to peak N concentration in leachate during the SR period. Additionally, soil wetness index (SWI) shaped spatial patterns of SWC, resulting in distinct spatial patterns of N2O emissions and nitrate leaching. Locations with higher SWI exhibited greater soil N2O flux and higher nitrate concentrations in leachate. This study emphasizes the significant effect of soil hydrological processes on soil N2O emissions and N leaching in hillslope ecosystems, providing valuable insights for N management in these environments.

Nitrous oxide fluxes during a winter cover crop season in a Mississippi corn cropping system

Agroecosystems are the largest source of anthropogenic N2O fluxes. While cover crops (CC) offer benefits for soil health, their impacts on greenhouse gas fluxes are inconsistent. In the southeastern US, where intensive agriculture and low CC adoption are prevalent, few studies have investigated CC impact on soil N2O fluxes. Our study explored the effects of CC species and management practices on soil N2O fluxes during the winter CC growing season in Mississippi, which was conducted in a non-tilled corn cropping system with seven CC treatments. We measured in situ soil N2O fluxes, along with soil moisture and temperature, throughout the CC growing season from 2022 to 2023. Surface soil samples were also collected to analyze soil mineral nitrogen (N) content and enzyme activity. Over the study period (a total of 188 days), cumulative N2O fluxes were 0.50–1.03 ​kg N2O–N ha−1, with the lowest values from the annually-rotated Elbon rye treatment and the highest from the annually-rotated Austrian winter pea. Our results show that both CC treatments and sampling time significantly affected soil N2O fluxes. There was a strong positive correlation (r ​= ​0.34, p ​< ​0.05) between N2O fluxes and NO3–N content, which was lowest under continuous rye and rotated-rye treatments (0.31 and 0.34 ​mg ​kg−1 ). The results suggest that Elbon rye effectively reduced soil N2O fluxes during this period by lowering the soil NO3–N content, the primary substrate for denitrification. This study is one of the few studies to examine the impacts of cover crops on soil N2O fluxes in cropping systems in the southeastern US, offering insights into the cover crop effects on soil N2O fluxes during their growing season.

White Clover does not Increase Soil N2O Emissions Compared to Ryegrass in Non-Frozen Winter, but Increases CH4 Uptake

As one of the most important forage species in Europe, white clover (Trifolium repens) is a legume that is well recognized for its potential to increase productivity especially under reduced N input. It is hypothesized that legumes have the potential to decrease overwinter soil greenhouse gas (GHG) emissions due to more efficient N recycling as compared to non-legume forbs. We conducted a field experiment recording high-resolution soil nitrous oxide (N2O) and methane (CH4) fluxes during the winter months (December 2019 to March 2020) on a five-year-old grassland in central Germany with white clover, fertilized and unfertilized perennial ryegrass (Lolium perenne), and bare soil. White clover and fertilized ryegrass stimulated soil N2O emissions by 174% and 212% as compared to bare soil, and by 36% and 56% as compared to unfertilized ryegrass, respectively, due to their greater N availability and higher water-filled pore space (WFPS). The estimated cumulative CH4 fluxes under white clover were a net CH4 sink, whereas ryegrass and bare soil were net CH4 sources. Soil N2O fluxes were predominantly regulated by both mineral N and WFPS, while CH4 fluxes were mainly explained by WFPS. N-fertilization during the growing season did not affect off-season N2O and CH4 fluxes in perennial ryegrass plots. The combined non-CO2 global warming potential highlighted the possible mitigation effect of white clover on overwinter GHG emissions. Our findings suggest that GHG emissions from legumes are not offsetting their productive benefits during the non-frozen winter seasons.

Carbon-scaled nitrous oxide emissions better reflect the impacts of land use changes than raw nitrous oxide emissions in the Dry Chaco region

In the Dry Chaco region, agriculture expansion has caused significant land use change hotspots. However, the post-impact of land use change on nitrous oxide (N2O) emissions and carbon (C) budgets remains unknown. This study aimed to contrast the impacts of the main land use systems on N2O emissions related to its C inputs and C budgets by comparing them with those of a native forest at two sites of the Dry Chaco region of Argentina. At Site 1, the land use system were soybean-fallow-soybean and maize-fallow-maize sequences, whereas at Site 2, it was a soybean-wheat sequence. Measurements of soil N2O and carbon dioxide (CO2) fluxes were carried out monthly using the static chamber method. The C budgets of each system were determined for the annual crop-fallow cycle by the difference between the C inputs (from annual aboveground (ABG), belowground (BG), and rhizodeposition) and C outputs (defined as cumulative CO2-C emissions). At Site 1, the native forest showed 168 and 50 % more cumulative N2O emissions than maize and soybean, respectively. However, most land use differences were based on C inputs. Thus, when the cumulative N2O emissions of each system were related to their C inputs, the N2O emissions per ton of C entered of the native forest were lower than those of soybean and similar to those of maize. The C budgets (± standard error) at Site 1 were 6.4 ± 1.3, 1.0 ± 0.3 and −0.7 ± 0.6 t C ha−1 yr−1 for native forest, maize and soybean, respectively. At Site 2, they were 3.1 ± 0.7 and −4.0 ± 0.6 t C ha−1 yr−1 for the native forest and the soybean-wheat sequence, respectively. This paper proposes a comprehensive approach that integrates C inputs and budgets when evaluating N2O emissions from different land uses as a guide to define mitigating management practices and considers a native vegetation system to unmask the real impacts of agroecosystems.

Nitrous Oxide Emissions and Ammonia Volatilization from Pasture after Cattle Dung and Urine Applications in the Dry and Rainy Seasons of the Brazilian Cerrado

An important source of greenhouse gases in Brazil is the nitrous oxide (N2O) emission from pasture, and microorganisms play an important role in nitrogen transformations in the soil. This study aimed to evaluate N2O emission and NH3 volatilization from bovine excreta in pasture in an integrated crop–livestock system (ICL) in the Brazilian Cerrado. Three treatments (urine, dung and control) were performed in two pastures (Area 1—three-year pasture of Urochloa ruziziensis and Area 2—one-year pasture of Urochloa brizantha cv. Piatã), with two application times of the excreta (dry and rainy season), during two successive years of application. Compared to the control, the excreta deposition on ICL increased soil N2O and NH3 fluxes. In the dry season, N2O fluxes were associated with higher ammonium (NH4+) availability. In the rainy season, these fluxes were related to NO3− availability and water-filled pore space (WFPS). In both areas, NH3 volatilization was higher after urine than dung application, especially in the dry season. The highest N2O emission factors were obtained for urine (0.32%), the rainy season (0.36%), and older pasture (Area 1: 0.24%). All these values were below the mean IPCC default values (0.77%). These results indicate that N2O emissions in pasture should be evaluated in regional conditions.

Deficit irrigation interacting with biochar mitigates N2O emissions from farmland in a wheat–maize rotation system

Biochar application to agricultural fields is an effective carbon sequestration measure that has the potential to reduce N2O emissions and increase soil water holding capacity. However, the interaction mechanisms of biochar under deficit irrigation on N2O emissions remain unclear. A two-year field experiment is conducted in the Guanzhong Plain, China, in order to quantify the effects of biochar and deficit irrigation on N2O emissions from winter wheat–summer maize crop rotation and to investigate the potential mechanisms of nitrification and denitrification. According to the combination of biochar application and actual evapotranspiration-based irrigation scheduling, four treatments are designed (B1W100: biochar 30 t·ha−1 + ET; B1W80: biochar 30 t·ha−1+ 0.8 ET; B0W100: no biochar + ET; B0W80: no biochar + 0.8ET). The soil N2O flux, soil physical and chemical properties, and key functional gene abundance related to N2O emissions in nitrification and denitrification at different growth stages are investigated and discussed. Results show that the interaction between deficit irrigation and biochar significantly reduces soil N2O emissions. During the wheat and maize season, the application of biochar reduces the N2O emissions by an average of 12.9% and 15.2%, respectively. Deficit irrigation also reduces the N2O emissions by an average of 17.4% and 15.5%, respectively. Pearson correlation analysis shows that soil N2O is significantly correlated with soil water-filled pore space during the phase with intense N2O emissions. Soil functional gene abundance is determined at different growth stages for both wheat and maize. Maximum soil denitrification functional gene abundance is observed at the time when wheat and maize enter the stage of their peak growth at the jointing stage. With biochar addition and deficit irrigation, the abundance of nirK and nosZ genes increases and AOB amoA genes decreases. These results suggest that biochar with deficit irrigation is a better solution to reduce N2O emissions from agricultural soils.

Impact of liming and maize residues on N2O and N2 fluxes in agricultural soils: an incubation study

AbstractSince it is known that nitrous oxide (N2O) production and consumption pathways are affected by soil pH, optimising the pH of agricultural soils can be an important approach to reduce N2O emissions. Because liming effects on N2O reduction had not been studied under ambient atmosphere and typical bulk density of arable soils, we conducted mesoscale incubation experiments with soils from two liming trials to investigate the impact of long-term pH management and fresh liming on N transformations and N2O production. Soils differed in texture and covered a range of pH levels (3.8–6.7), consisting of non-limed controls, long-term field-limed calcite and dolomite treatments, and freshly limed soils. Both soils were amended with 15N-labelled potassium nitrate (KNO3) and incubated with and without incorporated maize litter. Packed soil mesocosms were cycled through four phases of alternating temperatures and soil moistures for at least 40 days. Emissions of N2O and dinitrogen (N2) as well as the product ratio of denitrification N2O/(N2O + N2), referred to as N2Oi were measured with the 15N gas flux method in N2-reduced atmosphere. Emissions of N2O increased in response to typical denitrifying conditions (high moisture and presence of litter). Increased temperature and soil moisture stimulated microbial activity and triggered denitrification as judged from 15NO3− pool derived N2O + N2 emissions. Fresh liming increased denitrification in the sandy soil up to 3-fold but reduced denitrification in the loamy soil by 80%. N2Oi decreased throughout the incubation in response to fresh liming from 0.5–0.8 to 0.3–0.4, while field-limed soils had smaller N2Oi (0.1–0.3) than unlimed controls (0.9) irrespective of incubation conditions. Our study shows that the denitrification response (i.e., N2O + N2 production) to liming is soil dependent, whereas liming effects on N2Oi are consistent for both long- and short-term pH management. This extends previous results from anoxic slurry incubation studies by showing that soil pH management by liming has a good mitigation potential for agricultural N2O emissions from denitrification under wet conditions outside of cropping season.

Dry and wet periods determine stem and soil greenhouse gas fluxes in a northern drained peatland forest

Greenhouse gas (GHG) fluxes from peatland soils are relatively well studied, whereas tree stem fluxes have received far less attention. Simultaneous year-long measurements of soil and tree stem GHG fluxes in northern peatland forests are scarce, as previous studies have primarily focused on the growing season. We determined the seasonal dynamics of tree stem and soil CH4, N2O and CO2 fluxes in a hemiboreal drained peatland forest. Gas samples for flux calculations were manually collected from chambers at different heights on Downy Birch (Betula pubescens) and Norway Spruce (Picea abies) trees (November 2020–December 2021) and analysed using gas chromatography. Environmental parameters were measured simultaneously with fluxes and xylem sap flow was recorded during the growing season. Birch stems played a greater role in the annual GHG dynamics than spruce stems. Birch stems were net annual CH4, N2O and CO2 sources, while spruce stems constituted a CH4 and CO2 source but a N2O sink. Soil was a net CO2 and N2O source, but a sink of CH4. Temporal dynamics of stem CH4 and N2O fluxes were driven by isolated emissions' peaks that contributed significantly to net annual fluxes. Stem CO2 efflux followed a seasonal trend coinciding with tree growth phenology. Stem CH4 dynamics were significantly affected by the changes between wetter and drier periods, while N2O was more influenced by short-term changes in soil hydrologic conditions. We showed that CH4 emitted from tree stems during the wetter period can offset nearly half of the soil sink capacity. We presented for the first time the relationship between tree stem GHG fluxes and sap flow in a peatland forest. The net CH4 flux was likely an aggregate of soil-derived and stem-produced CH4. A dominating soil source was more evident for stem N2O fluxes.

Interrelationships of CO2, CH4, and N2O fluxes in snow-covered temperate soils, Northern Japan

This study focuses on assessing the concentrations, fluxes, and production rates of greenhouse gases (CO2, CH4, and N2O) in a cold temperate grassland soil underlying snowpack during the winter of 1996/7 in northern Japan. Results included mean ± standard deviation (range) correlation coefficients (R2) for CO2–CH4 concentrations and CO2–N2O concentrations of 0.93 ± 0.07 (0.81–0.99) and 0.96 ± 0.06 (0.83–0.99) for winter, and 0.74 ± 0.17 (0.55–0.92) and 0.96 ± 0.05 (0.88–0.99) for summer, respectively. This suggests close relationships between the mechanisms of CO2 and N2O production and the oxidation of CH4, which are influenced by factors such as oxygen availability, temperature, and moisture in the soil. Furthermore, the study found that winter fluxes of CO2–CH4 and CO2–N2O through the snowpack showed positive linear correlations. Winter CO2 emissions accounted for 96 % of the variability in CH4 oxidation and 77 % of the variability in N2O emissions. This demonstrates that winter CO2 emissions were affected to the magnitude of CH4 oxidations and N2O emissions in the soil. These findings have implications for the modification of terrestrial ecosystem models in temperate regions, particularly in assessing contributions from winter greenhouse gas fluxes to overall annual emissions. Understanding the interrelationships and dynamics of greenhouse gases throughout the year is crucial for accurate modeling and predictions of ecosystem responses to climate change.

Greenhouse gas emissions of sewage sludge land application in urban green space: A field experiment in a Bermuda grassland

Sewage sludge land application is recognized as a strategy for recycling resource and replenishing soil nutrients. However, the subsequent greenhouse gas emissions following this practice are not yet fully understood, and the lack of quantitative research and field experiments monitoring these emissions hampers the establishment of reliable emission factors. This study investigated the greenhouse gas emission characteristics of sewage sludge land application through a field experiment that monitoring soil greenhouse gas fluxes. Seven nitrogen input treatments were implemented in a typical Bermuda grassland in China, with D and C representing the amendment of digested and composted sludge, respectively, at the nitrogen input rate of 0, 100, 200, and 300 kg N ha−1. Soil CH4, CO2, and N2O fluxes were measured throughout the entire experimental period, and soil samples from different treatments at various growth stages were analyzed. The results revealed that sewage sludge land application significantly increased soil N2O and CO2 emissions while slightly reducing soil CH4 uptake. The increased CO2 emissions were biogenic and carbon-neutral, mainly due to enhanced plant root respiration. The N2O emissions were the primary greenhouse gas emissions of sewage sludge land application, which were mainly concentrated in two 50-day periods following base and topdressing fertilization, respectively. N2O emissions following base fertilization by rotary tillage were substantially lower than those following topdressing fertilization. A logarithmic response relationship between N input rates and increased soil N2O emissions was observed, suggesting lower N2O emissions from sewage sludge land application compared to conventional N fertilizers at the same N input level. Future field experiments and meta-analysis are necessary to develop reliable greenhouse gas emission factors for sewage sludge land application.

Effects of land use patterns on soil properties and nitrous oxide flux on a semi-arid environmental conditions of Loess Plateau China

Ecosystems and agroecosystems strongly influences the global warming by nitrogen oxide (N2O) emission. In a recent climate change scenario, nitrogen and carbon sequestration is obligatory under different land-use patterns. However, soil nitrogen elements and carbon content in the recover process of degraded environmental conditions on the Dingxi Loess Plateau has not been clearly understood. Thus, in this current study, we selected four representative land use patterns, including picea asperata (PA), which is based on forest land; Medicago sativa (MS), which is based on grassland; abandoned bare land (AL), which is based on abandoned land; and wheat field (WF), which is based on farmland, to study soil quality indicators and N2O greenhouse gas and relationships amongst environmental factors and N2O flux. Our results depicted that PA and MS significantly increased organic carbon (SOC), total phosphorous (TP), gravimetric water content (SWC), soil bulk density (BD), total nitrogen (TN), ammonium nitrogen (NH4+-N), and microbial biomass nitrogen (MBN) whist decreased soil nitrate nitrogen (NO3--N) content and soil pH value over AL land-use pattern. However, WF land-use pattern showed reduced trend of above mention studied parameters than AL. Additionally, compared to AL, PA and MS significantly reduced the total soil N2O emissions, with reductions of 24.91% and 14.77% in 2021 and 29.08% and 17.53% in 2022, respectively. The WF significantly increased the total N2O emissions, increasing by 53.18% and 40.37% in 2021 and 2022, respectively. Moreover, environmental variables for instance aerial temperature, precipitation had significant correlation with soil N2O based on linear regression analysis, soil NO3--N and soil temperature had significant positive correlation with soil N2O flux while NH4+-N, BD, and SWC were negatively correlated with N2O flux. The Partial Least Squares Path Model (PLS-PM) indicates that soil temperature and soil moisture was the dominant factor for controlling soil N2O emissions followed by soil nutrients and land use patterns. Accordingly, in the context of vegetation restoration process of the study area, the proportion of forest land and grassland should be increase to cope with future climate change scenario. This research result can provide theoretical basis and technical support for scientific understanding and evaluation of soil N2O emission mechanisms and nitrogen sink functions under different land-use patterns in semi-arid region of China.

Post-fire soil greenhouse gas fluxes in boreal Scots pine forests–Are they affected by surface fires with different severities?

Although forest fires are one of the main natural disturbance types in boreal forests, there is limited information regarding surface fires (dominant in Northern Europe), and how surface fires of different severities could affect post-fire soil greenhouse gas emissions. The results of our study show that fire severity, time since fire and post-fire changes in soil temperature were the main factors driving soil carbon dioxide (CO2) flux (forest floor ecosystem respiration) from burned boreal forest soils. Approximately two hours after the fire, soil CO2 emissions from burned areas were significantly higher compared to pre-fire conditions, and areas with high-severity fires had significantly higher soil CO2 emissions compared to those with low-severity fires. Later (days, months) after the fire, the unburned control areas always had higher soil CO2 emission values compared to burned areas. In the case of methane (CH4), time since fire and post-fire changes in soil temperatures were the main factors driving soil CH4 fluxes. Unburned study areas were sinks of CH4 through the entire measurement period, while immediately after the fire, the burned areas turned from CH4 sink to CH4 source. For nitrous oxide (N2O) measurements, time since fire was the only factor that significantly affected soil N2O fluxes. Shortly after the fire, N2O emissions increased significantly from both low- and high-intensity study plots. Two days after the fire, post-fire soil C and N content decreased in the O-horizon and increased within the first 5 cm of the soil mineral layer, and the trend was visible both in low- and high-severity fire plots. Samples collected four months after the fire, showed similar total soil C and N content as there was before the fire.

Impact of Soil Organic Layer Thickness on Soil-to-Atmosphere GHG Fluxes in Grassland in Latvia

Drained organic soils in agricultural land are considered significant contributors to total greenhouse gas (GHG) emissions, although the temporal and spatial variation of GHG emissions is high. Here, we present results of the study on soil-to-atmosphere fluxes of carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) from drained organic (fen) soils in grassland. A two-year study (from July 2021 to June 2023) was conducted in three research sites in Latvia (Europe’s hemiboreal zone). Soil total respiration (Rtot), CH4 and N2O fluxes were determined using a manual opaque chamber technique in combination with gas chromatography, while soil heterotrophic respiration (Rhet) was measured with a portable spectrometer. Among research sites, the thickness of the soil organic layer ranged from 10 to 70 cm and mean groundwater level ranged from 27 to 99 cm below the soil surface. Drained organic soil in all research sites was a net source of CO2 emissions (mean 3.48 ± 0.33 t CO2-C ha−1 yr−1). No evidence was obtained that the thickness of the soil organic layer (ranging from 10 to 70 cm) and OC stock in soil can be considered one of the main affecting factors of magnitude of net CO2 emissions from drained organic soil. Drained organic soil in grassland was mostly a source of N2O emissions (mean 2.39 ± 0.70 kg N2O-N ha−1 yr−1), while the soil both emitted and consumed atmospheric CH4 depending on the thickness of the soil organic layer (ranging from −3.26 ± 1.33 to 0.96 ± 0.10 kg CH4-C ha−1 yr−1).

Towards an integrated view on microbial CH4, N2O and N2 cycles in brackish coastal marsh soils: A comparative analysis of two sites

Coastal ecosystems, facing threats from global change and human activities like excessive nutrients, undergo alterations impacting their function and appearance. This study explores the intertwined microbial cycles of carbon (C) and nitrogen (N), encompassing methane (CH4), nitrous oxide (N2O), and nitrogen gas (N2) fluxes, to determine nutrient transformation processes between the soil-plant-atmosphere continuum in the coastal ecosystems with brackish water. Water salinity negatively impacted denitrification, bacterial nitrification, N fixation, and n-DAMO processes, but did not significantly affect archaeal nitrification, COMAMMOX, DNRA, and ANAMMOX processes in the N cycle. Plant species age and biomass influenced CH4 and N2O emissions. The highest CH4 emissions were from old Spartina and mixed Spartina and Scirpus sites, while Phragmites sites emitted the most N2O. Nitrification and incomplete denitrification mainly governed N2O emissions depending on the environmental conditions and plants. The higher genetic potential of ANAMMOX reduced excessive N by converting it to N2 in the sites with higher average temperatures. The presence of plants led to a decrease in the N fixers' abundance. Plant biomass negatively affected methanogenetic mcrA genes. Microbes involved in n-DAMO processes helped mitigate CH4 emissions. Over 93 % of the total climate forcing came from CH4 emissions, except for the Chinese bare site where the climate forcing was negative, and for Phragmites sites, where almost 60 % of the climate forcing came from N2O emissions. Our findings indicate that nutrient cycles, CH4, and N2O fluxes in soils are context-dependent and influenced by environmental factors and vegetation. This underscores the need for empirical analysis of both C and N cycles at various levels (soil-plant-atmosphere) to understand how habitats or plants affect nutrient cycles and greenhouse gas emissions.

Large contribution of soil N2O emission to the global warming potential of a large-scale oil palm plantation despite changing from conventional to reduced management practices

Abstract. Conventional management of oil palm plantations, involving high fertilization rate and herbicide application, results in high yield but with large soil greenhouse gas (GHG) emissions. This study aimed to assess a practical alternative to conventional management, namely reduced fertilization with mechanical weeding, to decrease soil GHG emissions without sacrificing production. We established a full factorial experiment with two fertilization rates (conventional and reduced fertilization, equal to nutrients exported via fruit harvest) and two weeding methods (herbicide and mechanical), each with four replicate plots, since 2016 in a ≥ 15-year-old, large-scale oil palm plantation in Indonesia. Soil CO2, N2O, and CH4 fluxes were measured during 2019–2020, and yield was measured during 2017–2020. Fresh fruit yield (30 ± 1 Mgha-1yr-1) and soil GHG fluxes did not differ among treatments (P≥ 0.11), implying legacy effects of over a decade of conventional management prior to the start of the experiment. Annual soil GHG fluxes were 5.5 ± 0.2 Mg CO2-C ha−1 yr−1, 3.6 ± 0.7 kg N2O-N ha−1 yr−1, and −1.5 ± 0.1 kg CH4-C ha−1 yr−1 across treatments. The palm circle, where fertilizers are commonly applied, covered 18 % of the plantation area but accounted for 79 % of soil N2O emission. The net primary production of this oil palm plantation was 17 150 ± 260 kgCha-1yr-1, but 62 % of this was removed by fruit harvest. The global warming potential of this planation was 3010 ± 750 kgCO2eqha-1yr-1, of which 55 % was contributed by soil N2O emission and only &lt; 2 % offset by the soil CH4 sink.

Regulatory potential of soil available carbon, nitrogen, and functional genes on N2O emissions in two upland plantation systems

Dynamic nitrification and denitrification processes are affected by changes in soil redox conditions, and they play a vital role in regulating soil N2O emissions in rice-based cultivation. It is imperative to understand the influences of different upland crop planting systems on soil N2O emissions. In this study, we focused on two representative rotation systems in Central China: rapeseed–rice (RR) and wheat–rice (WR). We examined the biotic and abiotic processes underlying the impacts of these upland plantings on soil N2O emissions. The results revealed that during the rapeseed-cultivated seasons in the RR rotation system, the average N2O emissions were 1.24±0.20 and 0.81±0.11 kg N ha−1 for the first and second seasons, respectively. These values were comparable to the N2O emissions observed during the first and second wheat-cultivated seasons in the WR rotation system (0.98±0.25 and 0.70±0.04 kg N ha−1, respectively). This suggests that upland cultivation has minimal impacts on soil N2O emissions in the two rotation systems. Strong positive correlations were found between N2O fluxes and soil ammonium (NH4+), nitrate (NO3−), microbial biomass nitrogen (MBN), and the ratio of soil dissolved organic carbon (DOC) to NO3− in both RR and WR rotation systems. Moreover, the presence of the AOA-amoA and nirK genes were positively associated with soil N2O fluxes in the RR and WR systems, respectively. This implies that these genes may have different potential roles in facilitating microbial N2O production in various upland plantation models. By using a structural equation model, we found that soil moisture, mineral N, MBN, and the AOA-amoA gene accounted for over 50% of the effects on N2O emissions in the RR rotation system. In the WR rotation system, soil moisture, mineral N, MBN, and the AOA-amoA and nirK genes had a combined impact of over 70% on N2O emissions. These findings demonstrate the interactive effects of functional genes and soil factors, including soil physical characteristics, available carbon and nitrogen, and their ratio, on soil N2O emissions during upland cultivation seasons under rice-upland rotations.