Quantifying Beetle-Mediated Effects on Gas Fluxes from Dung Pats

Agriculture is one of the largest contributors of the anthropogenic greenhouse gases (GHGs) responsible for global warming. Measurements of gas fluxes from dung pats suggest that dung is a source of GHGs, but whether these emissions are modified by arthropods has not been studied. A closed chamber system was used to measure the fluxes of carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) from dung pats with and without dung beetles on a grass sward. The presence of dung beetles significantly affected the fluxes of GHGs from dung pats. Most importantly, fresh dung pats emitted higher amounts of CO₂ and lower amounts of CH₄ per day in the presence than absence of beetles. Emissions of N₂O showed a distinct peak three weeks after the start of the experiment – a pattern detected only in the presence of beetles. When summed over the main grazing season (June–July), total emissions of CH₄ proved significantly lower, and total emissions of N₂O significantly higher in the presence than absence of beetles. While clearly conditional on the experimental conditions, the patterns observed here reveal a potential impact of dung beetles on gas fluxes realized at a small spatial scale, and thereby suggest that arthropods may have an overall effect on gas fluxes from agriculture. Dissecting the exact mechanisms behind these effects, mapping out the range of conditions under which they occur, and quantifying effect sizes under variable environmental conditions emerge as key priorities for further research.     

Biotechnologies for greenhouse gases (CH4, N2O, and CO2) abatement: state of the art and challenges

Today, methane (CH₄), nitrous oxide (N₂O), and carbon dioxide (CO₂) emissions represent approximately 98 % of the total greenhouse gas (GHG) inventory worldwide, and their share is expected to increase significantly in this twenty-first century. CO₂ represents the most important GHG with approximately 77 % of the total GHG emissions (considering its global warming potential) worldwide, while CH₄ and N₂O are emitted to a lesser extent (14 and 8 %, respectively) but exhibit global warming potentials 23 and 298 times higher than that of CO₂, respectively. Most members of the United Nations, based on the urgent need to maintain the global average temperature 2 °C above preindustrial levels, have committed themselves to significantly reduce their GHG emissions. In this context, an active abatement of these emissions will help to achieve these target emission cuts without compromising industrial growth. Nowadays, there are sufficient empirical evidence to support that biological technologies can become, if properly tailored, a low-cost and environmentally friendly alternative to physical/chemical methods for the abatement of GHGs. This study constitutes a state-of-the-art review of the microbiology (biochemistry, kinetics, and waste-to-value processes) and bioreactor technology of CH₄, N₂O, and CO₂ abatement. The potential and limitations of biological GHG degradation processes are critically discussed, and the current knowledge gaps and technology niches in the field are identified.     

Soil-atmosphere exchange of nitrous oxide and methane in New Zealand terrestrial ecosystems and their mitigation options: a review

The two non-CO₂ greenhouse gases (GHGs) nitrous oxide (N₂O) and methane (CH₄) comprise 54.8% of total New Zealand emissions. Nitrous oxide is mainly generated from mineral N originating from animal dung and urine, applied fertiliser N, biologically fixed N₂, and mineralisation of soil organic N. Even though about 96% of the anthropogenic CH₄ emitted in New Zealand is from ruminant animals (methanogenesis), methane uptake by aerobic soils (methanotrophy) can significantly contribute to the removal of CH₄ from the atmpsphere, as the global estimates confirm. Both the net uptake of CH₄ by soils and N₂O emissions from soils are strongly influenced by changes in land use and land management. Quantitative information on the fluxes of these two non-CO₂ GHGs is required for a range of land-use and land-management ecosystems to determine their contribution to the national emissions inventory, and for assessing the potential of mitigation options. Here we report soil N₂O fluxes and CH₄ uptake for a range of land-use and land-management systems collated from published and unpublished New Zealand studies. Nitrous oxide emissions are highest in dairy-grazed pastures (10–12 kg N₂O–N ha^?1 year^{? 1}), intermediate in sheep-grazed pastures, (4–6 kg N₂O–N ha^?1 year^?1), and lowest in forest, shrubland and ungrazed pasture soils (1–2 kg N₂O–N ha^?1 year^?1). N deposited in the form of animal urine and dung, and N applied as fertiliser, are the principal sources of N₂O production. Generally, N₂O emissions from grazed pasture soils are high when the soil water-filled pore-space is above field capacity, and net CH₄ uptake is low or absent. Although nitrification inhibitors have shown some promise in reducing N₂O emissions from grazed pasture systems, their efficacy as an integral part of farm management has yet to be tested. Methane uptake was highest for a New Zealand Beech forest soil (10–11 kg CH₄ ha^?1 year^?1), intermediate in some pine forest soils (4–6 kg CH₄ ha^?1 year^?1), and lowest in most pasture (<1 kg CH₄ ha^?1 year^?1) and cropped soils (1.5 kg CH₄ ha^?1 year^?1). Afforestation /reforestation of pastures results in increases in soil CH₄ uptake, largely as a result of increases in soil aeration status and changes in the population and activities of methanotrophs. Soil CH₄ uptake is also seasonally dependent, being about two to three times higher in a dry summer and autumn than in a wet winter. There are no practical ways yet available to reduce CH₄ emissions from agricultural systems. The mitigation options to reduce gaseous emissions are discussed and future research needs identified.     

Does hatchery-reared Siniperca chuatsi (Actinopterygii,Perciformes) compete significantly with two wild Siniperca populations for diets in a shallow lake?

Greenhouse gas emissions of Lake Neusiedl, the westernmost European shallow steppe lake, were analysed to identify differences between the seasons of the years and between different locations in the pelagic zone and reed belt. Emissions of CO₂, CH₄ and N₂O were measured in gas samples that had been recovered from the gas space of floating chambers operated as closed systems. Sampling periods covered all seasons except winter. Scaled up to the whole lake area (320 km²), the diffusive emissions of spring, summer and autumn totalled to about 79,500 t CO₂e, disregarding bubble emissions, winter emissions and plant-mediated emissions. The emission sum consisted of about 57,000 t CO₂, 760 t CH₄, and 12 t N₂O. Approximately one-third of the methane and carbon dioxide emissions originated in the pelagic zone and two-thirds in the reed belt (without plant emissions) whereas nitrous oxide emissions were similar in these two zones. An estimate of ebullitive emissions resulted in additional 1,765 t CH₄ that predominantly originated in or near the reed belt from spring to autumn.     

淡水水生生态系统温室气体排放的主要途径及影响因素研究进展

淡水水生生态系统是全球陆域生态系统的重要组成部分,近年来,关于淡水水生生态系统温室气体排放的研究日益增多。基于国内外目前对湖泊、河流、水库及浅水池塘等淡水生态系统开展的最新研究成果,总结分析了淡水水生生态系统温室气体排放的3个主要途径及相应观测方法。气泡排放的观测方法有倒置漏斗法、开放式动态箱法和超声探测技术;植物传输的观测方法有密闭箱法和植株切割法;扩散途径的观测方法有静态浮箱法、模型估算法/梯度法、微气象学法、TDLAS吸收光谱法等。从物理因素、化学因素、生物因素、水动力因素和人类活动等角度,深入探讨了淡水水生生态系统温室气体排放通量的影响因素。最后根据当前研究中存在的不足,对今后的研究方向提出了建议,以期为我国进一步深入开展相关研究提供借鉴。     

Effect of improved nitrogen management on greenhouse gas emissions from intensive dairy systems in the Netherlands

Dairy systems in Europe contribute to the emissions of the greenhouse gases (GHGs) nitrous oxide (N₂O), methane (CH₄) and carbon dioxide (CO₂). In this paper, the effects of improved nitrogen (N) management on GHG emissions from Dutch dairy farms are determined. The GHG emissions are calculated using the panel on climate change (IPCC) methodology for the Netherlands, an updated and refined IPCC methodology, and a full accounting approach. The changes in dairy farming over the last 20 years, and the consequences for N management are described using detailed farm‐level data, collected in 1985, 1997 and 2002. The selected years represent distinct stages in the implementation of N policies. The changes in N management have reduced the GHG emissions. A reduction of the N surplus per kilogram milk with 1 g N reduced the GHG emissions per kilogram milk with approximately 29 g CO₂‐equivalents. The reduction of the N surpluses was mainly brought about by reduced fertilizer use and reduced grazing time. The use of updated and refined emission factors resulted in higher CH₄ emissions and lower N₂O emissions. On average, the overall emission was 36% higher with the refined method. Full accounting, including all direct and indirect emissions of CH₄, N₂O and CO₂, increased the emission with 36% compared with the refined IPCC methodology. We conclude that the N surplus at farm level is a useful indicator of GHG emissions. A full accounting system as presented in this study may effectively enable farmers to address the issue of emissions of GHGs in their operational management decisions. Both approaches serve their own specific objectives: full accounting at the farm level to explore mitigation options, and the IPCC methods to report changes in GHG emissions at the national level.     

Annual emissions of greenhouse gases from sheepfolds in Inner Mongolia

Sheepfolds represent significant hot spot sources of greenhouse gases (GHG) in semi-arid grassland regions, such as Inner Mongolia in China. However, the annual contribution of sheepfolds to regional GHG emissions is still unknown. In order to quantify its annual contribution, we conducted measurements of carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) fluxes at two sheepfold sites in the Baiyinxile administrative region of Inner Mongolia for 1 year, using static opaque chamber and gas chromatography methods. Our data show that, at an annual scale, both sheepfolds functioned as net sources of CO₂, CH₄ and N₂O. Temperatures primarily determined the seasonal pattern of CO₂ emission; 60–84% of the CO₂ flux variation could be explained by temperature changes. High rates of net CH₄ emissions from sheepfold soils were only observed when animals (sheep and goats) were present. While nitrous oxide emissions were also stimulated by the presence of animals, pulses of N₂O emissions were also be related to rainfall and spring-thaw events. The total annual cumulative GHG emissions in CO₂ equivalents (CO₂: 1; CH₄: 25; and N₂O: 298) were quantified as 87.4?±?18.4 t ha^?1 for the sheepfold that was used during the non-grazing period (i.e., winter sheepfold) and 136.7?±?15.9 t ha^?1 used during the grazing period (i.e., summer sheepfold). Of the annual total GHG emissions, CH₄ release accounted for approximately 1% of emissions, while CO₂ and N₂O emissions contributed to approximately 59% and 40%, respectively. The total GHG emission factor (CO₂?+?CH₄?+?N₂O) per animal for the sheepfolds investigated in this study was 30.3 kg CO₂ eq yr^?1 head^?1, which translates to 0.3, 18.8 and 11.2 kg CO₂ eq yr^?1 head^?1 for CH₄, CO₂ and N₂O, respectively. Sheepfolds accounted for approximately 34% of overall N₂O emissions in the Baiyinxile administrative region, a typical steppe region within Inner Mongolia. The contribution of sheepfolds to the regional CO₂ or CH₄ exchange is marginal.     

Annual emissions of dissolved CO2, CH4, and N2O in the subsurface drainage from three cropping systems

Indirect emission of nitrous oxide (N₂O), associated with nitrogen (N) leaching and runoff from agricultural lands is a major source of atmospheric N₂O. Recent studies have shown that carbon dioxide (CO₂) and methane (CH₄) are also emitted via these pathways. We measured the concentrations of three dissolved greenhouse gases (GHGs) in the subsurface drainage from field lysimeter that had a shallow groundwater table. Aboveground fluxes of CH₄ and N₂O were monitored using an automated closed‐chamber system. The annual total emissions of dissolved and aboveground GHGs were compared among three cropping systems; paddy rice, soybean and wheat, and upland rice. The annual drainage in the paddy rice, the soybean and wheat, and the upland rice plots was 1435, 782, and 1010 mm yr^?1, respectively. Dissolved CO₂ emissions were highest in the paddy rice plots, and were equivalent to 1.05–1.16% of the carbon storage in the topsoil. Dissolved CH₄ emissions were also higher in the paddy rice plots, but were only 0.03–0.05% of the aboveground emissions. Dissolved N₂O emissions were highest in the upland rice plots, where leached N was greatest due to small crop biomass. In the soybean and wheat plots, large crop biomass, due to double cropping, decreased the drainage volume, and thus decreased dissolved GHG emissions. Dissolved N₂O emissions from both the soybean and wheat plots and the upland rice plots were equivalent to 50.3–67.3% of the aboveground emissions. The results indicate that crop type and rotation are important factors in determining dissolved GHG emissions in the drainage from a crop field.     

An exploration on greenhouse gas and ammonia production by insect species suitable for animal or human consumption

Background

Greenhouse gas (GHG) production, as a cause of climate change, is considered as one of the biggest problems society is currently facing. The livestock sector is one of the large contributors of anthropogenic GHG emissions. Also, large amounts of ammonia (NH₃), leading to soil nitrification and acidification, are produced by livestock. Therefore other sources of animal protein, like edible insects, are currently being considered.

Methodology/Principal Findings

An experiment was conducted to quantify production of carbon dioxide (CO₂) and average daily gain (ADG) as a measure of feed conversion efficiency, and to quantify the production of the greenhouse gases methane (CH₄) and nitrous oxide (N₂O) as well as NH₃ by five insect species of which the first three are considered edible: Tenebrio molitor, Acheta domesticus, Locusta migratoria, Pachnoda marginata, and Blaptica dubia. Large differences were found among the species regarding their production of CO₂ and GHGs. The insects in this study had a higher relative growth rate and emitted comparable or lower amounts of GHG than described in literature for pigs and much lower amounts of GHG than cattle. The same was true for CO₂ production per kg of metabolic weight and per kg of mass gain. Furthermore, also the production of NH₃ by insects was lower than for conventional livestock.

Conclusions/Significance

This study therefore indicates that insects could serve as a more environmentally friendly alternative for the production of animal protein with respect to GHG and NH₃ emissions. The results of this study can be used as basic information to compare the production of insects with conventional livestock by means of a life cycle analysis.     

Nitrous oxide and methane exchange in two small temperate forest catchments—effects of hydrological gradients and implications for global warming potentials of forest soils

The magnitude of greenhouse gas (GHG) flux rates may be important in wet and intermediate wet forest soils, but published estimates are scarce. We studied the surface exchange of methane (CH₄) and nitrous oxide (N₂O) from soil along toposequences in two temperate deciduous forest catchments: Strødam and Vestskoven. The soil water regime ranged from fully saturated to aerated within the catchments. At Strødam the largest mean flux rates of N₂O (15 μg N₂O-N m^?2 h^?1) were measured at volumetric soil water contents (SWC) between 40 and 60% and associated with low soil pH compared to smaller mean flux rates of 0-5 μg N₂O-N m^?2 h^?1 for drier (SWC < 40%) and wet conditions (SWC > 80%). At Vestskoven the same response of N₂O to soil water content was observed. Average CH₄ flux rates were highly variable along the toposequences (?17 to 536 μg CH₄-C m^?2 h^?1) but emissions were only observed above soil water content of 45%. Scaled flux rates of both GHGs to catchment level resulted in emission of 322 and 211 kg CO₂-equivalents ha^?1 year^?1 for Strødam and Vestskoven, respectively, with N₂O contributing the most at both sites. Although the wet and intermediate wet forest soils occupied less than half the catchment area at both sites, the global warming potential (GWP) derived from N₂O and CH₄ was more than doubled when accounting for these wet areas in the catchments. The results stress the importance of wet soils in assessments of forest soil global warming potentials, as even small proportions of wet soils contributes substantially to the emissions of N₂O and CH₄.     

高寒草地土壤温室气体排放对放牧的响应研究进展

高寒草地生态系统具有独特的地理环境和气候特征,对放牧干扰十分敏感,在全球温室气体通量中贡献突出,研究高寒草地放牧对土壤温室气体排放的影响机制具有重要意义。本文总结高寒草地温室气体源/汇特征、不同放牧方式对土壤微环境和微生物群落结构的影响,发现高寒草地主要是CO₂源、CH₄汇、N₂O源。放牧通过家畜选择性采食、践踏和排泄物返还等多重机制作用于地上植物、土壤结构、温度、湿度和养分,进而影响地下微生物及温室气体通量。本文旨在为高寒草地生态系统健康发展和管理及缓解全球气候变化提供科学依据,并对未来研究方向进行展望。     

Changes of methane and nitrous oxide emissions in a transition bog in central Germany (German National Park Harz Mountains) after rewetting

During the last decades, various renaturation programmes have been initialized to recover nutrient sink and ecological functions of peatlands by rewetting. Rewetting, however, often results in the formation of hotspots for methane (CH₄) emissions and in temporal dieback of local vegetation. The present study aimed at quantifying changes of CH₄ and nitrous oxide (N₂O) emissions in a peatland currently under continuous rewetting conditions. Emissions where studied at a permanently flooded site and a non-flooded peat site with fluctuating water tables by using common closed chamber method. The permanently flooded site revealed extremely high CH₄ emissions (up to 1195 mg C m^?2 d^?1) which were positively correlated with temperature, nutrient content, dissolved organic carbon and nitrogen concentration of the peat soil water. In contrast, the non-flooded peat site, with lower and fluctuating water tables (WT), showed significantly lower CH₄ emissions and an increasing trend of CH₄ release associated with a generally increasing WT caused by the progressing rewetting process. Lower N₂O emissions (<24 µg N m^?2 d^?1) were observed at the flooded site. By contrast, the non-flooded peat site with fluctuating WT showed significantly higher N₂O emissions (up to 4178 µg N m^?2 d^?1), in particular at high temperatures during summer time. The present results indicate that permanently flooded conditions during rewetting processes might cause higher CH₄ emissions compared to fluctuating WT which in contrast might enhance N₂O emissions. In total, however, no decreasing trend for CH₄ emissions throughout the five-year renaturation period could be found. At least for N₂O we observed a decreasing trend during rewetting.     

Trace gas flux and the influence of short-term soil water and temperature dynamics in Australian sheep grazed pastures of differing productivity

Temperate pastures are often managed with P fertilizers and N₂-fixing legumes to maintain and increase pasture productivity which may lead to greater nitrous oxide (N₂O) emissions and reduced methane (CH₄) uptake. However, the diel and inter-daily variation in N₂O and CH₄ flux in pastures is poorly understood, especially in relation to key environmental drivers. We investigated the effect of pasture productivity, rainfall, and changing soil moisture and temperature upon short-term soil N₂O and CH₄ flux dynamics during spring in sheep grazed pasture systems in southeastern Australia. N₂O and CH₄ flux was measured continuously in a High P (23 kg P ha^?1 yr^?1) and No P pasture treatment and in a sheep camp area in a Low P (4 kg P ha^?1 yr^?1) pasture for a four week period in spring 2005 using an automated trace gas system. Although pasture productivity was three-fold greater in the High P than No P treatment, mean CH₄ uptake was similar (?6.3?±?SE 0.3 to ?8.6?±?0.4 μg C m^?2 hr^?1) as were mean N₂O emissions (6.5 to 7.9?±?0.8 μg N m^?2 hr^?1), although N₂O flux in the No P pasture did not respond to changing soil water conditions. N₂O emissions were greatest in the Low P sheep camp (12.4 μg?±?1.1 N m^?2 hr^?1) where there were also net CH₄ emissions of 5.2?±?0.5 μg C m^?2 hr^?1. There were significant, but weak, relationships between soil water and N₂O emissions, but not between soil water and CH₄ flux. The diel temperature cycle strongly influenced CH₄ and N₂O emissions, but this was often masked by the confounding covariate effects of changing soil water content. There were no consistently significant differences in soil mineral N or gross N transformation rates, however, measurements of substrate induced respiration (SIR) indicated that soil microbial processes in the highly productive pasture are more N limited than P limited after >20 years of P fertilizer addition. Increased productivity, through P fertilizer and legume management, did not significantly increase N₂O emissions, or reduce CH₄ uptake, during this 4 week measurement period, but the lack of an N₂O response to rainfall in the No P pasture suggests this may be evident over a longer measurement period. This study also suggests that small compacted and nutrient enriched areas of grazed pastures may contribute greatly to the overall N₂O and CH₄ trace gas balance.     

Greenhouse gas emissions from dairy manure management: a review of field‐based studies

Livestock manure management accounts for almost 10% of greenhouse gas emissions from agriculture globally, and contributes an equal proportion to the US methane emission inventory. Current emissions inventories use emissions factors determined from small‐scale laboratory experiments that have not been compared to field‐scale measurements. We compiled published data on field‐scale measurements of greenhouse gas emissions from working and research dairies and compared these to rates predicted by the IPCC Tier 2 modeling approach. Anaerobic lagoons were the largest source of methane (368 ± 193 kg CH₄ hd^?1 yr^?1), more than three times that from enteric fermentation (~120 kg CH₄ hd^?1 yr^?1). Corrals and solid manure piles were large sources of nitrous oxide (1.5 ± 0.8 and 1.1 ± 0.7 kg N₂O hd^?1 yr^?1, respectively). Nitrous oxide emissions from anaerobic lagoons (0.9 ± 0.5 kg N₂O hd^?1 yr^?1) and barns (10 ± 6 kg N₂O hd^?1 yr^?1) were unexpectedly large. Modeled methane emissions underestimated field measurement means for most manure management practices. Modeled nitrous oxide emissions underestimated field measurement means for anaerobic lagoons and manure piles, but overestimated emissions from slurry storage. Revised emissions factors nearly doubled slurry CH₄ emissions for Europe and increased N₂O emissions from solid piles and lagoons in the United States by an order of magnitude. Our results suggest that current greenhouse gas emission factors generally underestimate emissions from dairy manure and highlight liquid manure systems as promising target areas for greenhouse gas mitigation.     

Annual net greenhouse gas balance in a halophyte (Helianthus tuberosus) bioenergy cropping system under various soil practices in Southeast China

A full accounting of net greenhouse gas balance (NGHGB) and greenhouse gas intensity (GHGI) was examined in an annual coastal reclaimed saline Jerusalem artichoke-fallow cropping system under various soil practices including soil tillage, soil ameliorant, and crop residue amendments. Seasonal fluxes of soil carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) were measured using static chamber method, and the net ecosystem exchange of CO₂ (NEE) was determined by the difference between soil heterotrophic respiration (R_H) and net primary production (NPP). Relative to no-tillage, rotary tillage significantly decreased the NPP of Jerusalem artichoke while it had no significant effects on the annual R_H. Rotary tillage increased CH₄ emissions, while seasonal or annual soil N₂O emissions did not statistically differ between the two tillage treatments. Compared with the control plots, soil ameliorant or straw amendment enhanced R_H, soil CH_4, and N₂O emissions under the both tillage regimes. Annual NGHGB was negative for all the field treatments, as a consequence of net ecosystem CO₂ sequestration exceeding the CO₂-equivalents released as CH₄ and N₂O emissions, which indicates that Jerusalem artichoke-fallow cropping system served as a net sink of GHGs. The annual net NGHGB and GHGI were estimated to be 11–21% and 4–8% lower in the NT than in RT cropping systems, respectively. Soil ameliorant and straw amendments greatly increased NPP and thus significantly decreased the negative annual net NGHGB. Overall, higher NPP but lower climatic impacts of coastal saline bioenergy production would be simultaneously achieved by Jerusalem artichoke cultivation under no-tillage with improved saline soil conditions in southeast China.     

Climatic role of terrestrial ecosystem under elevated CO2: a bottom‐up greenhouse gases budget

The net balance of greenhouse gas (GHG) exchanges between terrestrial ecosystems and the atmosphere under elevated atmospheric carbon dioxide (CO₂) remains poorly understood. Here, we synthesise 1655 measurements from 169 published studies to assess GHGs budget of terrestrial ecosystems under elevated CO₂. We show that elevated CO₂ significantly stimulates plant C pool (NPP) by 20%, soil CO₂ fluxes by 24%, and methane (CH₄) fluxes by 34% from rice paddies and by 12% from natural wetlands, while it slightly decreases CH₄ uptake of upland soils by 3.8%. Elevated CO₂ causes insignificant increases in soil nitrous oxide (N₂O) fluxes (4.6%), soil organic C (4.3%) and N (3.6%) pools. The elevated CO₂‐induced increase in GHG emissions may decline with CO₂ enrichment levels. An elevated CO₂‐induced rise in soil CH₄ and N₂O emissions (2.76 Pg CO₂‐equivalent year^?1) could negate soil C enrichment (2.42 Pg CO₂ year^?1) or reduce mitigation potential of terrestrial net ecosystem production by as much as 69% (NEP, 3.99 Pg CO₂ year^?1) under elevated CO₂. Our analysis highlights that the capacity of terrestrial ecosystems to act as a sink to slow climate warming under elevated CO₂ might have been largely offset by its induced increases in soil GHGs source strength.     

CO2 uptake is offset by CH4 and N2O emissions in a poplar short‐rotation coppice

The need for renewable energy sources will lead to a considerable expansion in the planting of dedicated fast‐growing biomass crops across Europe. These are commonly cultivated as short‐rotation coppice (SRC), and currently poplar (Populus spp.) is the most widely planted. In this study, we report the greenhouse gas (GHG) fluxes of carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) measured using eddy covariance technique in an SRC plantation for bioenergy production. Measurements were made during the period 2010–2013, that is, during the first two rotations of the SRC. The overall GHG balance of the 4 years of the study was an emission of 1.90 (±1.37) Mg CO₂eq ha^?1; this indicated that soil trace gas emissions offset the CO₂ uptake by the plantation. CH₄ and N₂O contributed almost equally to offset the CO₂ uptake of ?5.28 (±0.67) Mg CO₂eq ha^?1 with an overall emission of 3.56 (±0.35) Mg CO₂eq ha^?1 of N₂O and of 3.53 (±0.85) Mg CO₂eq ha^?1 of CH₄. N₂O emissions mostly occurred during one single peak a few months after the site was converted to SRC; this peak comprised 44% of the total N₂O loss during the two rotations. Accurately capturing emission events proved to be critical for deriving correct estimates of the GHG balance. The nitrogen (N) content of the soil and the water table depth were the two drivers that best explained the variability in N₂O and CH_4, respectively. This study underlines the importance of the ‘non‐CO₂ GHGs’ on the overall balance. Further long‐term investigations of soil trace gas emissions should monitor the N content and the mineralization rate of the soil, as well as the microbial community, as drivers of the trace gas emissions.     

Effect of biochar amendment on the soil-atmosphere exchange of greenhouse gases from an intensive subtropical pasture in northern New South Wales, Australia

We assessed the effect of biochar incorporation into the soil on the soil-atmosphere exchange of the greenhouse gases (GHG) from an intensive subtropical pasture. For this, we measured N₂O, CH₄ and CO₂ emissions with high temporal resolution from April to June 2009 in an existing factorial experiment where cattle feedlot biochar had been applied at 10 t ha^?1 in November 2006. Over the whole measurement period, significant emissions of N₂O and CO₂ were observed, whereas a net uptake of CH₄ was measured. N₂O emissions were found to be highly episodic with one major emission pulse (up to 502 ??g N₂O-N m^?2 h^?1) following heavy rainfall. There was no significant difference in the net flux of GHGs from the biochar amended vs. the control plots. Our results demonstrate that intensively managed subtropical pastures on ferrosols in northern New South Wales of Australia can be a significant source of GHG. Our hypothesis that the application of biochar would lead to a reduction in emissions of GHG from soils was not supported in this field assessment. Additional studies with longer observation periods are needed to clarify the long term effect of biochar amendment on soil microbial processes and the emission of GHGs under field conditions.     

Simultaneous numerical representation of soil microsite production and consumption of carbon dioxide,methane, and nitrous oxide using probability distribution functions

Production and consumption of nitrous oxide (N₂O), methane (CH₄), and carbon dioxide (CO₂) are affected by complex interactions of temperature, moisture, and substrate supply, which are further complicated by spatial heterogeneity of the soil matrix. This microsite heterogeneity is often invoked to explain non‐normal distributions of greenhouse gas (GHG) fluxes, also known as hot spots and hot moments. To advance numerical simulation of these belowground processes, we expanded the Dual Arrhenius and Michaelis–Menten model, to apply it consistently for all three GHGs with respect to the biophysical processes of production, consumption, and diffusion within the soil, including the contrasting effects of oxygen (O₂) as substrate or inhibitor for each process. High‐frequency chamber‐based measurements of all three GHGs at the Howland Forest (ME, USA) were used to parameterize the model using a multiple constraint approach. The area under a soil chamber is partitioned according to a bivariate log‐normal probability distribution function (PDF) of carbon and water content across a range of microsites, which leads to a PDF of heterotrophic respiration and O₂ consumption among microsites. Linking microsite consumption of O₂ with a diffusion model generates a broad range of microsite concentrations of O₂, which then determines the PDF of microsites that produce or consume CH₄ and N₂O, such that a range of microsites occurs with both positive and negative signs for net CH₄ and N₂O flux. Results demonstrate that it is numerically feasible for microsites of N₂O reduction and CH₄ oxidation to co‐occur under a single chamber, thus explaining occasional measurement of simultaneous uptake of both gases. Simultaneous simulation of all three GHGs in a parsimonious modeling framework is challenging, but it increases confidence that agreement between simulations and measurements is based on skillful numerical representation of processes across a heterogeneous environment.     

Measurement and prediction of enteric methane emission

The greenhouse gas (GHG) emissions from the agricultural sector account for about 25.5% of total global anthropogenic emission. While CO₂ receives the most attention as a factor relative to global warming, CH₄, N₂O and chlorofluorocarbons (CFCs) also cause significant radiative forcing. With the relative global warming potential of 25 compared with CO₂, CH₄ is one of the most important GHGs. This article reviews the prediction models, estimation methodology and strategies for reducing enteric CH₄ emissions. Emission of CH₄ in ruminants differs among developed and developing countries, depending on factors like animal species, breed, pH of rumen fluid, ratio of acetate:propionate, methanogen population, composition of diet and amount of concentrate fed. Among the ruminant animals, cattle contribute the most towards the greenhouse effect through methane emission followed by sheep, goats and buffalos, respectively. The estimated CH₄ emission rate per cattle, buffaloe, sheep and goat in developed countries are 150.7, 137, 21.9 and 13.7 (g/animal/day) respectively. However, the estimated rates in developing countries are significantly lower at 95.9 and 13.7 (g/animal/day) per cattle and sheep, respectively. There exists a strong interest in developing new and improving the existing CH₄ prediction models to identify mitigation strategies for reducing the overall CH₄ emissions. A synthesis of the available literature suggests that the mechanistic models are superior to empirical models in accurately predicting the CH₄ emission from dairy farms. The latest development in prediction model is the integrated farm system model which is a process-based whole-farm simulation technique. Several techniques are used to quantify enteric CH₄ emissions starting from whole animal chambers to sulfur hexafluoride (SF6) tracer techniques. The latest technology developed to estimate CH₄ more accurately is the micrometeorological mass difference technique. Because the conditions under which animals are managed vary greatly by country, CH₄ emissions reduction strategies must be tailored to country-specific circumstances. Strategies that are cost effective, improve productivity, and have limited potential negative effects on livestock production hold a greater chance of being adopted by producers. It is also important to evaluate CH₄ mitigation strategies in terms of the total GHG budget and to consider the economics of various strategies. Although reductions in GHG emissions from livestock industries are seen as high priorities, strategies for reducing emissions should not reduce the economic viability of enterprises.