Evaluating long-term ivermectin use and the role of dung beetles in reducing short-term CH4 and CO2 emissions from livestock faeces: a mesocosm design under Mediterranean conditions

1. Greenhouse gas (GHG) emissions from livestock contribute significantly to global warming, and a reduction of this source of emissions is crucial in achieving the goal of mitigating global warming. 2. CO₂ and CH₄ emissions from dung pats were analysed by means of a mesocosm experiment in a Mediterranean ecosystem. The experiment consisted of a total of 30 mesocosms distributed across three treatments: a well-preserved, undisturbed dung beetle assemblage associated with organic livestock; a dung beetle assemblage that was impoverished as a result of the long-term use of veterinary medical products; and a control treatment without dung beetles. 3. Corrections related to insect respiration allow researchers to provide more precise measurements of CO₂ emissions from dung, especially in the initial and final phases of dung exposure, when the percentage of CO₂ emitted by dung beetles can become greater than the emissions from the dung pats themselves. 4. The effects of dung beetles on CO₂ and CH₄ emissions are much more accentuated in warm-temperate conditions than in northern temperate areas previously studied. Mediterranean assemblages remove and spread dung faster and more effectively than do northern dung beetle assemblages characterised by a lower functional richness and beetle abundance and biomass. 5. From a livestock management viewpoint, mesocosms representing areas with impoverished dung beetle assemblages, due to the long-term use of veterinary medical products, such as ivermectin, emitted 1.6- and 2.8-fold higher total CO₂ and CH₄, respectively, than mesocosms mimicking sites with untreated livestock.     

Influence of experimental extreme water pulses on greenhouse gas emissions from soils

Climate models predict increased frequency and intensity of storm events, but it is unclear how extreme precipitation events influence the dynamics of soil fluxes for multiple greenhouse gases (GHGs). Intact soil mesocosms (0–10 cm depth) from a temperate forested watershed in the piedmont region of Maryland [two upland forest soils, and two hydric soils (i.e., wetland, creek bank)] were exposed to experimental water pulses with periods of drying, forcing soils towards extreme wet conditions under controlled temperature. Automated measurements (hourly resolution) of soil CO₂, CH₄, and N₂O fluxes were coupled with porewater chemistry analyses (i.e., pH, Eh, Fe, S, NO₃ ^?), and polymerase chain reaction–denaturing gradient gel electrophoresis to characterize changes in microbial community structure. Automated measurements quantified unexpected increases in emissions up to 245% for CO₂ (Wetland), >23,000% for CH₄ (Creek), and >110,000% for N₂O (Forest Soils) following pulse events. The Creek soil produced the highest soil CO₂ emissions, the Wetland soil produced the highest CH₄ emissions, and the Forest soils produced the highest N₂O emissions during the experiment. Using carbon dioxide equivalencies of the three GHGs, we determined the Creek soil contributed the most to a 20-year global warming potential (GWP; 30.3%). Forest soils contributed the most to the 100-year GWP (up to 53.7%) as a result of large N₂O emissions. These results provide insights on the influence of extreme wet conditions on porewater chemistry and factors controlling soil GHGs fluxes. Finally, this study addresses the need to test biogeochemical thresholds and responses of ecosystem functions to climate extremes.     

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.     

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。     

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.     

Progress in the studies on the greenhouse gas emissions from reservoirs

The green credentials of hydroelectricity in terms of greenhouse-gas (GHG) emissions have been tarnished with the finding of the researches on GHG emissions from hydroelectric reservoirs in the last two decades. Substantial amounts of GHGs release from the tropical reservoirs, especially methane (CH₄) from Brazil’s Amazonian areas. CH₄ contributes strongly to climate change because it has a global warming potential (GWP) 24 times higher than carbon dioxide (CO₂) on a per molecule basis over a 100-year time horizon. GHGs may emit from reservoirs through four different pathways to the atmosphere: (1) diffusive flux at the reservoir surface, (2) gas bubble flux in the shallow zones of a reservoir, (3) water degassing flux at the outlet of the powerhouse downstream of turbines and spillways, and (4) flux across the air–water interface in the rivers downstream of the dams. This paper reviewed the productions and emissions of CH₄, CO₂, and N₂O in reservoirs, and the environmental variables influencing CH₄ and CO₂ emissions were also summarized. Moreover, the paper combined with the progress of GHG emissions from Three Gorges Reservoir and proposed three crucial problems to be resolved on GHG emissions from reservoirs at present, which would be benefit to estimate the total GHG emissions from Three Gorges Reservoir accurately.     

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.     

Spatial Variation of Soil CO<Subscript>2</Subscript>, CH<Subscript>4</Subscript> and N<Subscript>2</Subscript>O Fluxes Across Topographical Positions in Tropical Forests of the Guiana Shield

The spatial variation of soil greenhouse gas fluxes (GHG; carbon dioxide—CO₂, methane—CH₄ and nitrous oxide—N₂O) remains poorly understood in highly complex ecosystems such as tropical forests. We used 240 individual flux measurements of these three GHGs from different soil types, at three topographical positions and in two extreme hydric conditions in the tropical forests of the Guiana Shield (French Guiana, South America) to (1) test the effect of topographical positions on GHG fluxes and (2) identify the soil characteristics driving flux variation in these nutrient-poor tropical soils. Surprisingly, none of the three GHG flux rates differed with topographical position. CO₂ effluxes covaried with soil pH, soil water content (SWC), available nitrogen and total phosphorus. The CH₄ fluxes were best explained by variation in SWC, with soils acting as a sink under drier conditions and as a source under wetter conditions. Unexpectedly, our study areas were generally sinks for N₂O and N₂O fluxes were partly explained by total phosphorus and available nitrogen concentrations. This first study describing the spatial variation of soil fluxes of the three main GHGs measured simultaneously in forests of the Guiana Shield lays the foundation for specific studies of the processes underlying the observed patterns.     

Impact of Grazing Intensity and Seasons on Greenhouse Gas Emissions in Tropical Grassland

Greenhouse gases (GHG) can be affected by grazing intensity, soil, and climate variables. This study aimed at assessing GHG emissions from a tropical pasture of Brazil to evaluate (i) how the grazing intensity affects the magnitude of GHG emissions; (ii) how season influences GHG production and consumption; and (iii) what are the key driving variables associated with GHG emissions. We measured under field conditions, during two years in a palisade-grass pasture managed with 3 grazing intensities: heavy (15 cm height), moderate (25 cm height), and light (35 cm height) N₂O, CH₄ and CO₂ fluxes using static closed chambers and chromatographic quantification. The greater emissions occurred in the summer and the lower in the winter. N₂O, CH₄, and CO₂ fluxes varied according to the season and were correlated with pasture grazing intensity, temperature, precipitation, % WFPS (water-filled pores space), and soil inorganic N. The explanatory variables differ according to the gas and season. Grazing intensity had a negative linear effect on annual cumulative N₂O emissions and a positive linear effect on annual cumulative CO₂ emissions. Grazing intensity, season, and year affected N₂O, CH₄, and CO₂ emissions. Tropical grassland can be a large sink of N₂O and CH₄. GHG emissions were explained for different key driving variables according to the season.     

Responses of CO2, N2O and CH4 fluxes between atmosphere and forest soil to changes in multiple environmental conditions

To investigate the effects of multiple environmental conditions on greenhouse gas (CO₂, N₂O, CH₄) fluxes, we transferred three soil monoliths from Masson pine forest (PF) or coniferous and broadleaved mixed forest (MF) at Jigongshan to corresponding forest type at Dinghushan. Greenhouse gas fluxes at the in situ (Jigongshan), transported and ambient (Dinghushan) soil monoliths were measured using static chambers. When the transported soil monoliths experienced the external environmental factors (temperature, precipitation and nitrogen deposition) at Dinghushan, its annual soil CO₂ emissions were 54% in PF and 60% in MF higher than those from the respective in situ treatment. Annual soil N₂O emissions were 45% in PF and 44% in MF higher than those from the respective in situ treatment. There were no significant differences in annual soil CO₂ or N₂O emissions between the transported and ambient treatments. However, annual CH₄ uptake by the transported soil monoliths in PF or MF was not significantly different from that at the respective in situ treatment, and was significantly lower than that at the respective ambient treatment. Therefore, external environmental factors were the major drivers of soil CO₂ and N₂O emissions, while soil was the dominant controller of soil CH₄ uptake. We further tested the results by developing simple empirical models using the observed fluxes of CO₂ and N₂O from the in situ treatment and found that the empirical models can explain about 90% for CO₂ and 40% for N₂O of the observed variations at the transported treatment. Results from this study suggest that the different responses of soil CO₂, N₂O, CH₄ fluxes to changes in multiple environmental conditions need to be considered in global change study.     

Change in fluxes of carbon dioxide,methane and nitrous oxide due to forest drainage of mire sites of different trophy

Northern peatlands accumulate atmospheric CO₂ thus counteracting climate warming. However, CH₄ which is more efficient as a greenhouse gas than CO₂, is produced in the anaerobic decomposition processes in peat. When peatlands are taken for forestry their water table is lowered by ditching. We studied long-term effects of lowered water table on the development of vegetation and the annual emissions of CO₂, CH₄ and N₂O in an ombrotrophic bog and in a minerotrophic fen in Finland. Reclamation of the peat sites for forestry had changed the composition and coverage of the field and ground layer species, and increased highly the growth of tree stand at the drained fen. In general, drainage increased the annual CO₂ emissions but the emissions were also affected by the natural fluctuations of water table. In contrast to CO₂, drainage had decreased the emissions of CH₄, the drained fen even consumed atmospheric CH₄. CO₂ and CH₄ emissions were higher in the virgin fen than in the virgin bog. There were no N₂O emissions from neither type of virgin sites. Drainage had, however, highly increased the N₂O emissions from the fen. The results suggest that post-drainage changes in gas fluxes depend on the trophy of the original mires.     

Canopy soil greenhouse gas dynamics in response to indirect fertilization across an elevation gradient of tropical montane forests

Canopy soils can significantly contribute to aboveground labile biomass, especially in tropical montane forests. Whether they also contribute to the exchange of greenhouse gases is unknown. To examine the importance of canopy soils to tropical forest‐soil greenhouse gas exchange, we quantified gas fluxes from canopy soil cores along an elevation gradient with 4 yr of nutrient addition to the forest floor. Canopy soil contributed 5–12 percent of combined (canopy + forest floor) soil CO₂ emissions but CH₄ and N₂O fluxes were low. At 2000 m, phosphorus decreased CO₂ emissions (>40%) and nitrogen slightly increased CH₄ uptake and N₂O emissions. Our results show that canopy soils may contribute significantly to combined soil greenhouse gas fluxes in montane regions with high accumulations of canopy soil. We also show that changes in fluxes could occur with chronic nutrient deposition.     

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.     

Greenhouse gas budget (CO2, CH4 and N2O) of intensively managed grassland following restoration

The first full greenhouse gas (GHG) flux budget of an intensively managed grassland in Switzerland (Chamau) is presented. The three major trace gases, carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) were measured with the eddy covariance (EC) technique. For CO₂ concentrations, an open‐path infrared gas analyzer was used, while N₂O and CH₄ concentrations were measured with a recently developed continuous‐wave quantum cascade laser absorption spectrometer (QCLAS). We investigated the magnitude of these trace gas emissions after grassland restoration, including ploughing, harrowing, sowing, and fertilization with inorganic and organic fertilizers in 2012. Large peaks of N₂O fluxes (20–50 nmol m^?2 s^?1 compared with a <5 nmol m^?2 s^?1 background) were observed during thawing of the soil after the winter period and after mineral fertilizer application followed by re‐sowing in the beginning of the summer season. Nitrous oxide (N₂O) fluxes were controlled by nitrogen input, plant productivity, soil water content and temperature. Management activities led to increased variations of N₂O fluxes up to 14 days after the management event as compared with background fluxes measured during periods without management (<5 nmol m^?2 s^?1). Fluxes of CO₂ remained small until full plant development in early summer 2012. In contrast, methane emissions showed only minor variations over time. The annual GHG flux budget was dominated by N₂O (48% contribution) and CO₂ emissions (44%). CH₄ flux contribution to the annual budget was only minor (8%). We conclude that recently developed multi‐species QCLAS in an EC system open new opportunities to determine the temporal variation of N₂O and CH₄ fluxes, which further allow to quantify annual emissions. With respect to grassland restoration, our study emphasizes the key role of N₂O and CO₂ losses after ploughing, changing a permanent grassland from a carbon sink to a significant carbon source.     

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.     

Role of the aquatic pathway in the carbon and greenhouse gas budgets of a peatland catchment

Peatland streams have repeatedly been shown to be highly supersaturated in both CO₂ and CH₄ with respect to the atmosphere, and in combination with dissolved (DOC) and particulate organic carbon (POC) represent a potentially important pathway for catchment greenhouse gas (GHG) and carbon (C) losses. The aim of this study was to create a complete C and GHG (CO₂, CH₄, N₂O) budget for Auchencorth Moss, an ombrotrophic peatland in southern Scotland, by combining flux tower, static chamber and aquatic flux measurements from 2 consecutive years. The sink/source strength of the catchment in terms of both C and GHGs was compared to assess the relative importance of the aquatic pathway. During the study period (2007–2008) the catchment functioned as a net sink for GHGs (352 g CO₂‐Eq m^?2 yr^?1) and C (69.5 g C m^?2 yr^?1). The greatest flux in both the GHG and C budget was net ecosystem exchange (NEE). Terrestrial emissions of CH₄ and N₂O combined returned only 4% of CO₂ equivalents captured by NEE to the atmosphere, whereas evasion of GHGs from the stream surface returned 12%. DOC represented a loss of 24% of NEE C uptake, which if processed and evaded downstream, outside of the catchment, may lead to a significant underestimation of the actual catchment‐derived GHG losses. The budgets clearly show the importance of aquatic fluxes at Auchencorth Moss and highlight the need to consider both the C and GHG budgets simultaneously.     

Large Greenhouse Gas Emissions from a Temperate Peatland Pasture

Agricultural drainage is thought to alter greenhouse gas emissions from temperate peatlands, with CH₄ emissions reduced in favor of greater CO₂ losses. Attention has largely focussed on C trace gases, and less is known about the impacts of agricultural conversion on N₂O or global warming potential. We report greenhouse gas fluxes (CH₄, CO₂, N₂O) from a drained peatland in the Sacramento-San Joaquin River Delta, California, USA currently managed as a rangeland (that is, pasture). This ecosystem was a net source of CH₄ (25.8 ± 1.4 mg CH₄-C m⁻² d⁻¹) and N₂O (6.4 ± 0.4 mg N₂O-N m⁻² d⁻¹). Methane fluxes were comparable to those of other managed temperate peatlands, whereas N₂O fluxes were very high; equivalent to fluxes from heavily fertilized agroecosystems and tropical forests. Ecosystem scale CH₄ fluxes were driven by “hotspots” (drainage ditches) that accounted for less than 5% of the land area but more than 84% of emissions. Methane fluxes were unresponsive to seasonal fluctuations in climate and showed minimal temporal variability. Nitrous oxide fluxes were more homogeneously distributed throughout the landscape and responded to fluctuations in environmental variables, especially soil moisture. Elevated CH₄ and N₂O fluxes contributed to a high overall ecosystem global warming potential (531 g CO₂-C equivalents m⁻² y⁻¹), with non-CO₂ trace gas fluxes offsetting the atmospheric “cooling” effects of photoassimilation. These data suggest that managed Delta peatlands are potentially large regional sources of greenhouse gases, with spatial heterogeneity in soil moisture modulating the relative importance of each gas for ecosystem global warming potential.     

Challenges in the measurement of emissions of nitrous oxide and methane from livestock sector

Over the past two decades, the interest to decrease the emission levels of greenhouse gases (GHGs) has increased. The livestock sector has been put under continuous supervision and regulation because it is an important source of GHG emissions. In 2012, it was estimated that 3.46 Gton CO₂-eq was released from this sector, methane (CH₄) being the gas with the highest contribution (43 %), followed by nitrous oxide (21 %). In order to determine real emissions, it is necessary to use precise and reproducible measuring methods which can be complex and expensive. The challenges in these methods are focused on achieving an accurate assessment and monitoring of gas emissions, developing monitoring systems for the continuous measurement and implementation of methodologies for their validation in field in order to understand the complex nature of environmental variables affecting gas production. Different techniques for the measurement of CH₄ and nitrous oxide (N₂O) emissions are reviewed and discussed in this research. The passive flux sampling to measure emissions of these GHGs has been identified as an interesting alternative technique because it is practical, low cost and robust. This kind of sampler is highly adequate to measure emissions of N₂O and CH₄ originating from some sources of the livestock sector, but at this moment, no prototypes are commercially available and thus more research is necessary in this field.     

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。     

华南地区尾巨桉和马占相思人工林地表温室气体通量

为探索华南地区尾巨桉人工林和马占相思人工林地表温室气体的季节排放规律、排放通量和主控因子,采用静态箱-气相色谱法,对两种林型地表3种温室气体(CO_2、CH_4、N_2O)通量进行为期1年的逐月测定。结果表明:(1)尾巨桉人工林和马占相思人工林均为CO_2和N_2O的排放源,CH_4的吸收汇。马占相思林地表N_2O通量显著(P0.01)高于尾巨桉林,CO_2通量和CH_4通量无明显差异。(2)两种林型3种温室气体通量有着相似季节变化规律,地表CO_2通量均呈现雨季高旱季低的单峰规律;地表CH_4吸收通量表现为旱季高雨季低的单峰趋势;地表N_2O通量呈现雨季高旱季低且雨季内有两个峰值的排放规律。(3)地表CO_2、N_2O通量和土壤5 cm温度呈极显著(P0.01)正相关,3种温室气体地表通量同土壤含水量呈极显著(P0.01)或显著相关(P0.05)。(4)尾巨桉林和马占相思林温室气体年温室气体排放总量为31.014 t/hm~2和28.782 t/hm~2,均以CO_2排放占绝对优势(98.46%—99.15%),CH_4和N_2O处于次要地位。