新疆天山高寒草原不同放牧管理下的CO2,CH4和N2O通量特征

The invasions of the alien species such as Spartina alterniflora along the northern Jiangsu coastlines have posed a threat to biodiversity and the ecosystem function. Yet, limited attention has been given to their potential influence on greenhouse gas (GHG) emissions, including the diurnal variations of GHG fluxes that are fundamental in estimating the carbon and nitrogen budget. In this study, we examined the diurnal variation in fluxes of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) from a S. alterniflora intertidal flat in June, October, and December of 2013 and April of 2014 representing the summer, autumn, winter, and spring seasons, respectively. We found that the average CH4 fluxes on the diurnal scale were positive during the growing season while negative otherwise. The tidal flat of S. alterniflora acted as a source of CH4 in summer (June) and a combination of source and sink in other seasons. We observed higher diurnal variations in the CO2 and N2O fluxes during the growing season (1 536.5 mg CO2 m–2 h–1 and 25.6 μg N2O m–2 h–1) compared with those measured in the non-growing season (379.1 mg CO2 m–2 h–1 and 16.5 μg N2O m–2 h–1). The mean fluxes of CH4 were higher at night than that in the daytime during all the seasons but October. The diurnal variation in the fluxes of CO2 in June and N2O in December fluctuated more than that in October and April. However, two peak curves in October and April were observed for the diurnal changes in CO2 and N2O fluxes (prominent peaks were found in the morning of October and in the afternoon of April, respectively). The highest diurnal variation in the N2O fluxes took place at 15:00 (86.4 μg N2O m–2 h–1) in June with an unimodal distribution. Water logging in October increased the emission of CO2 (especially at nighttime), yet decreased N2O and CH4 emissions to a different degree on the daily scale because of the restrained diffusion rates of the gases. The seasonal and diurnal variations of CH4 and CO2 fluxes did not correlate to the air and soil temperatures, whereas the seasonal and diurnal variation of the fluxes of N2O in June exhibited a significant correlation with air temperature. When N2O and CH4 fluxes were converted to CO2-e equivalents, the emissions of N2O had a remarkable potential to impact the global warming. The mean daily flux (MF) and total daily flux (TDF) were higher in the growing season, nevertheless, the MF and TDF of CO2 were higher in October and those of CH4 and N2O were higher in June. In spite of the difference in the optimal sampling times throughout the observation period, our results obtained have implications for sampling and scaling strategies in estimating the GHG fluxes in coastal saline wetlands.

Whether natural wetlands serve as the source or sink of greenhouse gases (GHGs) remains uncertain. Wetlands in China are diverse in type and abundant in quantity and differ greatly in spatial distribution, environmental conditions, and GHG fluxes. However, few studies focused on the differences in GHG emissions from different types of natural wetlands. Here, we adopted strict data collection criteria to create comprehensive and detailed datasets of fluxes of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) from the marsh, coastal, lake, and river wetlands in China, and relevant environmental variables. Our study synthesized 265 field observations on GHGs that lasted at least one year (covering both the growing season and non-growing season) from 109 studies, among which CO2 measurements using the opaque chamber method were not included for eliminating the influence of absence of photosynthesis on net CO2 accounting. We found that CH4 contributed the largest warming effect among the three types of GHGs, and coastal and river wetlands respectively acted as the mitigators and motivators of global warming among the four types of wetlands. Correlation and regression analyses suggested that geographic location, soil moisture and organic carbon, and contents of nitrogen, phosphorus, and dissolved oxygen jointly drove wetland GHG fluxes. The comprehensive global warming potential of Chinese natural wetlands was estimated as 427 Tg CO2-equivalents year-1, which might result from increased wetland drainage, reclamation, and external nutrient inputs. This study highlights the incorporation of the full year-round GHG monitoring data without using opaque chambers to measure CO2 flux when extrapolating net GHG emissions and gives implications for natural wetland management and global warming mitigation strategies.

Carbon dioxide, methane and nitrous oxide fluxes from a fire chronosequence in subarctic boreal forests of Canada

Relationships among soil factors and greenhouse gas emissions from furrow-irrigated Rice in the mid-southern, USA

Agriculture in the midwestern United States is a major anthropogenic source of nitrous oxide (NO) and is both a source and sink for methane (CH), but the degree to which cropping systems differ in emissions of these gases is not well understood. Our objectives were to determine if fluxes of NO and CH varied among cropping systems and among crop phases within a cropping system. We compare NO and CH fluxes over the 2010 and 2011 growing seasons from the six cropping systems at the Wisconsin Integrated Cropping Systems Trial (WICST), a 20-yr-old cropping systems experiment. The study is composed of three grain and three forage cropping systems spanning a spectrum of crop diversity and perenniality that model a wide range of realistic cropping systems that differ in management, crop rotation, and fertilizer regimes. Among the grain systems, cumulative growing season NO emissions were greater for continuous corn ( L.) (3.7 kg NO-N ha) than corn-soybean [ (L.) Merr.] (2.0 kg NO-N ha) or organic corn-soybean-wheat ( L.) (1.7 kg NO-N ha). Among the forage systems, cumulative growing-season NO emissions were greater for organic corn-alfalfa ( L.)-alfalfa (2.9 kg NO-N ha) and conventional corn-alfalfa-alfalfa-alfalfa (2.5 kg NO-N ha), and lower for rotational pasture (1.9 kg NO-N ha). Application of mineral or organic N fertilizer was associated with elevated NO emissions. Yield-scaled emissions (kg NO-N Mg) did not differ by cropping system. Methane fluxes were highly variable and no effect of cropping system was observed. These results suggest that extended and diversified cropping systems could reduce area-scaled NO emissions from agriculture, but none of the systems studied significantly reduced yield-scaled NO emissions.

Understanding nitrous oxide (N2O) and methane (CH4) fluxes from agricultural soils in semi‐arid climates is necessary to fully assess greenhouse gas emissions from bioenergy cropping systems, and to improve our knowledge of global terrestrial gaseous exchange. Canola is grown globally as a feedstock for biodiesel production, however, resulting soil greenhouse gas fluxes are rarely reported for semi‐arid climates. We measured soil N2O and CH4 fluxes from a rain‐fed canola crop in a semi‐arid region of south‐western Australia for 1 year on a subdaily basis. The site included N fertilized (75 kg N ha−1 yr−1) and nonfertilized plots. Daily N2O fluxes were low (−1.5 to 4.7 g N2O‐N ha−1 day−1) and culminated in an annual loss of 128 g N2O‐N ha−1 (standard error, 12 g N2O‐N ha−1) from N fertilized soil and 80 g N2O‐N ha−1 (standard error, 11 g N2O‐N ha−1) from nonfertilized soil. Daily CH4 fluxes were also low (−10.3 to 11.9 g CH4‐C ha−1 day−1), and did not differ with treatments, with an average annual net emission of 6.7 g CH4–C ha−1 (standard error, 20 g CH4–C ha−1). Greatest daily N2O fluxes occurred when the soil was fallow, and following a series of summer rainfall events. Summer rainfall increased soil water contents and available N, and occurred when soil temperatures were >25 °C, and when there was no active plant growth to compete with soil microorganisms for mineralized N; conditions known to promote N2O production. The proportion of N fertilizer emitted as N2O, after correction for emissions from the no N fertilizer treatment, was 0.06%; 17 times lower than IPCC default value for the application of synthetic N fertilizers to land (1.0%). Soil greenhouse gas fluxes from bioenergy crop production in semi‐arid regions are likely to have less influence on the net global warming potential of biofuel production than in temperate climates.

Aim: The paper presents the results of the study of the dynamics of methane and carbon dioxide fluxes for the ridge-hollow oligotrophic bog complex in the middle taiga subzone of Western Siberia. Correlations between carbon dioxide and methane fluxes were revealed and the influence of meteorological parameters on greenhouse gas fluxes was estimated. Methods: Greenhouse gas fluxes were measured using the KASM8 chamber automatic monitoring system with eight transparent chambers and LI-COR LI-7810 gas analyser to analyze CO₂, CH₄ and H₂O concentrations. Results: The mean values of CO2 and CH4 fluxes for the study period were obtained; differences in the functioning of the ridge and the hollow are shown: median values of CO2 fluxes indicate a greater uptake on the ridge (-74.4 mgCO2/m2/h) than on the hollow (-52.7 mgCO2/m2/h); methane fluxes on the ridge (0.08 mgCH4/m2/h) are on average 20 times lower than on the hollow (2.76 mgCH4/m2/h). Correlation of greenhouse gas fluxes with environmental factors were revealed: the highest correlations were found with the intensity of incoming solar (r = -0.84 ÷ -0.91) and photosynthetically active radiation (r = -0.85 ÷ -0.92), air temperature (r = -0.51 ÷ -0.63) and relative air humidity (r = +0.56 ÷ +0.62) and wind speed (r = +0.39 ÷ +0.50). Conclusions: Correlations between specific greenhouse gas fluxes were estimated based on spatial and temporal flux variability data. Correlations between greenhouse gas fluxes are different at night and daytime, which is directly related to external factors and principles of ecosystem functioning.

During 2010-2013, we investigated the effects of stump harvesting on greenhouse gas (GHG) fluxes of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) with the flux-gradient technique at four experimental plots in a hemiboreal forest in Sweden. All plots were clear-cut and soil scarified and two of the plots were additionally stump harvested. The two clear-cut plots served as control plots. Due to differences in topography, we had one wetter and one drier plot of each treatment. All plots exhibited substantial emissions of GHGs and we noted significant effects of wetness on CO2, CH4 and N2O fluxes within treatments and significant effects of stump harvesting on CO2 and N2O fluxes at the dry plots. The CO2 emissions were lower at the dry stump harvested plot than at the dry control, but when estimated emissions from the removed stumps were added, total CO2 emissions were higher at the stump harvested plot, indicating a small enhancement of soil respiration. In addition, we noted significant emissions of N2O at this plot. At the wet plots, CO2 emissions were higher at the stump harvested plot, also suggesting a treatment effect but differences in wetness and vegetation cover at these plots make this effect more uncertain. At the wet plots, we noted sustained periods (weeks to months) of net N2O uptake. During the year with simultaneous measurements of the abovementioned GHGs, GHG budgets were 1.224×103 and 1.442×103 gm-2 of CO2-equivalents at the wet and dry stump harvested plots, respectively, and 1.070×103 and 1.696×103 gm-2 of CO2-equivalents at the wet and dry control plots, respectively. CO2 fluxes dominated GHG budgets at all plots but N2O contributed with 17% at the dry stump harvested plot. For the full period 2010-2013, total carbon (CO2+CH4) budgets were 4.301×103 and 4.114×103 g m-2 of CO2-eqvivalents at the wet and dry stump harvest plots, respectively and 4.107×103 and 5.274×103 gm-2 of CO2-equivalents at the wet and dry control plots, respectively. Our results support recent studies suggesting that stump harvesting does not result in substantial increase in CO2 emissions but uncertainties regarding GHG fluxes (especially N2O) remain and more long-term measurements are needed before robust conclusions can be drawn.

Urban landscapes contain a mix of land-use types with different patterns of nitrogen (N) cycling and export. We measured nitrate (NO(3)(-)) leaching and soil:atmosphere nitrous oxide (N(2)O) flux in four urban grassland and eight forested long-term study plots in the Baltimore, Maryland metropolitan area. We evaluated ancillary controls on these fluxes by measuring soil temperature, moisture, and soil:atmosphere fluxes of carbon dioxide on these plots and by sampling a larger group of forest, grass, and agricultural sites once to evaluate soil organic matter, microbial biomass, and potential net N mineralization and nitrification. Annual NO(3)(-) leaching ranged from 0.05 to 4.1 g N m(-2) yr(-1) and was higher in grass than forest plots, except in a very dry year and when a disturbed forest plot was included in the analysis. Nitrous oxide fluxes ranged from 0.05 to >0.3 g N m(-2) yr(-1), with few differences between grass and forest plots and markedly higher fluxes in wet years. Differences in NO(3)(-) leaching and N(2)O flux between forests and grasslands were not as high as expected given the higher frequency of disturbance and fertilization in the grasslands. Carbon dioxide flux, organic matter, and microbial biomass were as high or higher in urban grasslands than in forests, suggesting that active carbon cycling creates sinks for N in vegetation and soil in these ecosystems. Although urban grasslands export more N to the environment than native forests, they have considerable capacity for N retention that should be considered in evaluations of land-use change.

A system for simultaneous and continuous measurement of fluxes of three major greenhouse gases, carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O), from croplands was developed based on the closed chamber method. Controlled by a computer, top-lids of the chambers placed in the field closed periodically, remained closed for about 30 min, and then opened again. During the closure of the chambers, the air in the chambers was circulated by air pumps, and part of the circulated air was injected to gas analyzers. CO2 concentration was monitored with an infra-red gas analyzer, and its increasing/decreasing rate during the 1-3-min period after the chamber closure was used for the flux calculation. Concentrations of CH4 and N2O were measured with two gas chromatographs 4 times at intervals of 8.5 min. The system was tested in lysimeter fields with Gray lowland soil under various conditions, including paddy rice cultivation, upland crop cultivation and also fallow condition. Both CH4 and N2O concentrations in the chambers increased linearly or remained almost constant during the 30-min period after the chamber closure. CO2 concentration in the chambers also increased (which indicates the predominance of respiratory CO2 emission by the crops and/or soil microorganisms) or decreased (which indicates the predominance of photosynthetic CO2 uptake by the crops) linearly during the 1-3-min period after the chamber closure. These results indicated that appropriate fluxes could be estimated for all the three gases based on the gas concentration measurements with adequate time intervals, and on the linear regression analyses. The system is expected to be effective for clarifying the comprehensive dynamics of greenhouse gases in, and for estimating the total net global warming potential of croplands. Furthermore, simultaneous measurement of the fluxes of multiple gases is also effective for analyzing the mutual relationships and mechanisms of the gas fluxes. Changes in environmental factors such as increase in air temperature or decrease in light intensity during the chamber closure (generally referred to as “chamber effect”) should be taken into account as a cause of error in the flux data.

Limited information is available about soil nitrous oxide (NO) fluxes, NO emission factors (EFs), and yield-scaled NO emissions for biogas residues used to fertilize crops in semiarid regions. To address this knowledge gap, a 4-yr field experiment was conducted in a semiarid climate to determine growing season NO fluxes from soil receiving (i) anaerobically digested solid beef cattle manure (digestate), (ii) separated solids from the digestate (separated solids), and (iii) undigested solid beef cattle manure (cattle manure) applied to target one and two times the recommended rates (200 and 400 kg total N ha) for barley ( L.) forage, assuming 50% of N was annually plant available. Nitrous oxide fluxes were determined using vented static chambers. Over the four growing seasons, 95, 80, and 81% of the NO flux occurred within 36 d of applying digestate, separated solids, and cattle manure, respectively. The cumulative NO emissions with digestate were 4.7 and 4.1 times the values of the separated solids and cattle manure, respectively. The digestate NO EF was 13.6 and 10.6 times the values of the separated solids and cattle manure, respectively, but the NO EF based on applied mineral N was similar for all amendments. The yield-scaled NO emissions with digestate were 4.3 and 3.6 times the values of the separated solids and cattle manure, respectively. In the semiarid region of southern Alberta, liquid biogas residues have a higher risk for NO emissions than both the separated solid fraction of the biogas residues and undigested cattle manure.

Wetland catchments are major ecosystems in the Prairie Pothole Region (PPR) and play an important role in greenhouse gases (GHG) flux. However, there is limited information regarding effects of land-use on GHG fluxes from these wetland systems. We examined the effects of grazing and haying, two common land-use practices in the region, on GHG fluxes from wetland catchments during 2007 and 2008. Fluxes of methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2), along with soil water content and temperature, were measured along a topographic gradient every other week during the growing season near Ipswich, SD, USA. Closed, opaque chambers were used to measure fluxes of soil and plant respiration from native sod catchments that were grazed or left idle, and from recently restored catchments which were seeded with native plant species; half of these catchments were hayed once during the growing season. Catchments were adjacent to each other and had similar soils, soil nitrogen and organic carbon content, precipitation, and vegetation. When compared with idle catchments, grazing as a land-use had little effect on GHG fluxes. Likewise, haying had little effect on fluxes of CH4 and N2O compared with non-hayed catchments. Haying, however, did have a significant effect on combined soil and vegetative CO2 flux in restored wetland catchments owing to the immediate and comprehensive effect haying has on plant productivity. This study also examined soil conditions that affect GHG fluxes and provides cumulative annual estimates of GHG fluxes from wetland catchment in the PPR.

Carbon storage and greenhouse gases emission from a fluvial reservoir in an agricultural landscape

Shallow lakes are a key component of the global carbon cycle. It is, therefore, important to know how shallow lake ecosystems will respond to the current climate change. Global warming affects not only average temperatures, but also the frequency of heat waves (HW). The impact of extreme events on ecosystems processes, particularly greenhouse gas (GHG) emissions, is uncertain. Using the world's longest‐running shallow lake experiment, we studied the effects of a simulated summer HW on the fluxes of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). The experimental mesocosms had been exposed to different temperature treatments and nutrient loading for 11 years prior to the artificial HW. In general, there was an increase in total GHG emissions during the 1‐month artificial HW, with a significant increase in CO2, CH4 and N2O being observed in the shallow lake mesocosms. No significant effect of the HW on CO2 emissions could be traced, though, in the mesocosms with high nutrient levels. Furthermore, the data suggested that in addition to the direct effect of increased temperature on metabolic processes during the HW, biotic interactions exerted a significant control of GHG emissions. For example, at low nutrient levels, increased CO2 emissions were associated with low macrophyte abundance, whereas at high nutrient levels, decreased phytoplankton abundance was linked to increased emissions of CO2 and CH4. In contrast to the observable heat‐wave effect, no clear general effect of the long‐term temperature treatments could be discerned over the summer, likely because the potential effects of the moderate temperature increase, applied as a press disturbance, were overridden by biotic interactions. This study demonstrates that the role of biotic interactions needs to be considered within the context of global warming on ecosystem processes.

Free‐air carbon dioxide enrichment (FACE) experiments in terrestrial ecosystems have demonstrated ecological responses of key ecosystem processes to rising atmospheric carbon dioxide (CO2). However, CO2 fertilization responses in field conditions have seldom included methane (CH4) and nitrous oxide (N2O), particularly in natural and mature forests, which are expected to have an important role in climate change mitigation. Herein, we aimed to capture the effect of elevated CO2 (eCO2; ambient vs. +150 ppm) on long‐term temporal dynamics of CH4 and N2O fluxes, followed by identification of climo‐edaphic factors explaining feedback responses. To achieve this, continuous monitoring of greenhouse gas (GHG) fluxes using a manual chamber technique, over a 3‐year period was implemented in a mature dryland Eucalypt forest FACE (EucFACE) facility in Australia. The relationship between CH4 and N2O fluxes with rainfall indices and soil properties was also explored since they directly impact the microbial communities in the soil responsible for CH4 and N2O net emissions. Our results showed that in 3 years of eCO2 treatment, the amount and frequency of rainfall predicted GHG emissions in this native forest. We also found a significant reduction in CH4 sink (15%–25%) for some of the years as well as an overall treatment effect index reduction in N2O emissions under eCO2. Higher frequency of rain events with lower intensity led to highest CH4 sink followed by lowest N2O emissions due to fewer wet–dry cycles. Of all the environmental variables included, soil moisture, rainfall and pH were the main predictors of net CH4 and N2O emissions. Methane flux was also strongly influenced by soil texture. Our findings highlight the need to account for reduced forest CH4 sink under eCO2 in dryland ecosystems, which has implications for GHG budget predictions under future climate conditions. A free Plain Language Summary can be found within the Supporting Information of this article.