Search

Background and aims: In wetland ecosystems, the litter of emergent macrophytes generally begins to decay while standing, but aerial decomposition has often been overlooked. The goal of this study was therefore to elucidate the processes involved in the decomposition of standing litter of emergent macrophytes in freshwater marshes in the Sanjiang Plain, Northeast China. Methods: We used the litterbag method to quantify litter mass loss, microbial respiration rates, and nutrient dynamics of four common emergent macrophytes ( Carex lasiocarpa, Deyeuxia angustifolia, Glyceria spiculosa, and Phragmites australis) during one year of aerial decomposition. Results: Following one year of aerial decomposition, the leaf and culm mass losses were 19.3-45.1 % and 14.3-23.1 %, respectively. Litter mass loss was closely related to microbial respiration rates and initial ratios of C:N and C:P. The fact that litter N concentrations increased during aerial decomposition resulted in net N immobilization. After one year of decay, however, there was a net release of P from the standing litter in all cases, but the temporal pattern of P concentrations varied between the decomposing litter of the four different species. Conclusions: Our results provide evidence that the decomposition of standing litter from emergent macrophytes contributes markedly to overall litter decay, and thus is a key component of C and nutrient cycles in temperate wetlands. [ABSTRACT FROM AUTHOR]

To clarify the responses of plant functional traits to nitrogen (N) enrichment, we investigated the whole-plant traits (plant height and aboveground biomass), leaf morphological (specific leaf area (SLA) and leaf dry mass content (LDMC)) and chemical traits (leaf N concentration (LNC) and leaf phosphorus (P) concentration (LPC)) of Deyeuxia angustifolia and Glyceria spiculosa following seven consecutive years of N addition at four rates (0 g N/(m·yr), 6 g N/(m·yr), 12 g N/(m·yr) and 24 g N/(m·yr)) in a freshwater marsh in the Sanjiang Plain, Northeast China. The results showed that, for both D. angustifolia and G. spiculosa, N addition generally increased plant height, leaf, stem and total aboveground biomass, but did not cause changes in SLA and LDMC. Moreover, increased N availability caused an increase in LNC, and did not affect LPC. Thus, N addition decreased leaf C:N ratio, but caused an increase in leaf N:P ratio, and did not affect leaf C:P ratio. Our results suggest that, in the mid-term, elevated N loading does not alter leaf morphological traits, but causes substantial changes in whole-plant traits and leaf chemical traits in temperate freshwater wetlands. These may help to better understand the effects of N enrichment on plant functional traits and thus ecosystem structure and functioning in freshwater wetlands. [ABSTRACT FROM AUTHOR]

Freezing-thawing cycle (FTC) is an important environmental factor affecting soil physicochemical properties and microbial activities. The effects of FTC at mid-high latitudes, especially in the permafrost regions impacted by global warming, have become a hot topic for research. However, the responses of active organic carbon fractions and soil enzyme activities to FTC in the active layers of permafrost regions remain far from certain. In this study, soil samples from three soil layers of (0-15, 15-30 and 30-45 cm) an undisturbed peatlands in Da Xing'anling Mountains, Northeast China, were collected, and then subjected to various FTCs with a large (10 to −10 °C) and a small (5 to −5 °C) amplitudes, respectively. Results showed that the soil active organic carbon fractions and enzyme activities were sensitive to FTCs. The FTCs significantly increased water-extracted organic carbon (WEOC) concentration in the three soil layers by approximately 5-28 % for the large amplitude and 22-36 % for the small amplitude. In contrast, FTCs significantly decreased microbial biomass carbon (MBC) concentration, cellulase, amylase and invertase activities. Overall, the damage of FTCs to soil enzymes was severe at the deeper soil depths and for the large amplitude. Interestingly, the soil WEOC concentration was lower at the large amplitude of FTC compared with the small amplitude. When the numbers of FTCs increased, WEOC concentration began to decrease and MBC concentration and enzyme activities began to increase. In addition, the significant correlations between active organic carbon fractions and enzyme activities indicate that the increased WEOC by FTCs plays an important role in soil microbes and enzyme activities. [ABSTRACT FROM AUTHOR]

The Sanjiang Plain is the largest freshwater wetlands in Northeast China. In order to feed the growing population, about 84 % of the wetlands in this area have been converted to farmland, especially to paddy fields, since the 1950s. However, little is known about the influence of this conversion on soil microbial community composition. In this study, soil samples were collected from two natural wetlands dominated by plant species Carex lasiocarpa and Deyeuxia angustifolia and from a neighboring paddy field that was changed from wetland more than 10 years ago. The composition and diversity of bacterial communities in the soils were estimated by clone library analysis of nearly full length of 16S rDNA sequences. The results revealed that bacterial diversity was higher in paddy fields, and that the composition of bacterial communities differed among the three samples; the difference was more notable between the paddy field and two natural wetlands than between two natural wetlands. The distribution of clones into different bacterial phyla differed among soil samples, and the conversion from natural wetlands to paddy field increased the abundance of Proteobacteria and Firmicutes but decreased the abundance of Chloroflexi. About 63 % and 71 % of clones from two natural wetlands and 49 % of clones from the paddy field had <93 % similarity with known bacteria, suggesting that the majority of bacteria in natural wetland soils in the Sanjiang Plain are phylogenetically novel. In general, this study demonstrated that long-term conversion from natural wetlands to paddy field changes soil bacterial communities in the Sanjiang Plain. [ABSTRACT FROM AUTHOR]

Soil freezing-thawing cycle (FTC) is an important factor controlling C dynamics in mid-high latitude regions, especially in the permafrost regions impacted by global warming. Nonetheless, the response of C cycling in the deeper active layers of permafrost regions to FTC remains far from certain. We aimed to characterize the emission of CO2 from soils of multiple depths as impacted by FTC and its relationship with active organic C (OC) and enzyme activities. We collected soil samples from three soil layers (0-15, 15-30, and 30-45 cm) of an undisturbed peatland in the Da Xing'anling Mountains, NE China, and then subjected them to various freezing (10 to -10°C) and thawing (-10 to 10°C) cycles. Soil CO2 emissions, two active OC fractions, and activities of three enzymes were monitored during incubation periods. At the thawing stage of the first FTC, CO2 emission rates in the three soil layers presented transient peaks being ≈ 1.6-1.7 times higher than those of the unfrozen control sample. Although FTC did not change the overall patterns of decreasing CO2 emission along the soil profile, FTC significantly reduced the amount of CO2 emission when compared with the unfrozen control sample, possibly because the small CO2 emission at the freezing stage neutralized the peak of CO2 emission at the thawing stage. This study suggests that in the active layer of permafrost peatlands, CO2 emission during FTCs may be lower than the emission under higher temperatures, but experiment with more temperature gradients should be encouraged to verify this conclusion in the future. Meanwhile, FTC significantly increased water extracted OC release from the three soil layers, ≈ 1.2-1.6 times higher compared to the unfrozen control sample, indicating that soil carbon loss in the form of leachate may increase during freezing-thawing periods. Additionally, the CO2 emissions impacted by FTCs were significantly correlated with active OC fractions and enzyme activities, which indicated that active OC and enzymes were sensitive to FTCs, and surviving microbes and enzymes might use the increased liable substrates and induce the CO2 emission during freezing-thawing periods. [ABSTRACT FROM AUTHOR]

Abstract: Peatlands are the significant source of atmospheric methane (CH4), which is produced during peat accumulation. In this study, we investigated CH4 emissions over two growing seasons from a Carex lasiocarpa-dominated peatland in the Sanjiang Plain in China using the static chamber technique. We also investigated the environmental factors controlling emissions during the two years of study, 2012 and 2013. CH4 emissions ranged from 0.07 to 56.01 mg CH4–C m−2 h−1 with mean values of 7.33 ± 1.65 mg C m−2 h−1, showing significant temporal patterns in both years with peak values in early June and middle August respectively. Variations in water table, soil temperature at 25 cm depth and soil's water-filled pore space together explained 66.7% of the observed temporal variation of CH4 fluxes by the step-wise regression. Rapid and short-lived precipitation events might have no immediate influence on CH4 emissions, which primarily depended on the actual soil aeration and moisture conditions. A simple relationship between single parameter and CH4 fluxes would be overruled once the water table dropped below the critical threshold for CH4 release. The amount of CH4 emitted from the herbaceous peatland in the Sanjiang Plain during the growing season was about 6.93 × 1012 mg C. Our results suggested that the herbaceous peatland in the Sanjiang Plain is an important source of atmospheric CH4. [Copyright &y& Elsevier]

Abstract: Although methane (CH4) fluxes from northern wetlands in Asia have been described in previous research at different temporal and spatial scales, integrated studies at the ecosystem scale were scarce. In this study, CH4 fluxes were measured using eddy covariance (EC) technique and the chamber method in a cool temperate marsh in northeast China during the growing season (May&#x2013;September) of 2011. CH4 emissions were highly variable, both temporally and spatially during the measurement period. According to the EC observation data, CH4 fluxes showed a significant diurnal cycle during the mid-growing season with nighttime average flux about 67% of the average daytime values. Daily cumulative CH4 fluxes varied from 54 to 250 mg CH4 m&#x2212;2 d&#x2212;1 with an average flux of 136.2 mg CH4 m&#x2212;2 d&#x2212;1. The observations of chamber method showed that CH4 emissions differed markedly among the three main plant communities. Average flux at the Carex lasiocarpa site was about 4 times and 13.5 times of that at the Glyceria spiculosa site and Deyeuxia angustifolia site, respectively. The spatial variability of CH4 flux was mainly controlled by the varying water table level as well as the spatial distribution of different vascular plants, while the seasonal dynamic of CH4 emission could be best explained by the change of surface soil temperature and air pressure. A comparison was made between EC measurements and the upscaled chamber based model. The results from the model overestimated CH4 emission by 28% compared to the EC data. Considering the large variability of methane emission, it is necessary to conduct continuous observations on CH4 emission from northern wetlands at different temporal and spatial scales to comprehend the variability and also to predict responses to climate change. [ABSTRACT FROM AUTHOR]

Freezing-thawing in mid-high latitudes is an important factor controlling nutrient dynamics. We transplanted peatland columns (TQ) and freshwater marsh columns (SJ) in different latitudes into south seasonal frozen regions to determine the responses of greenhouse gas emissions from different wetlands to the freezing-thawing under climate warming. The decrease in CO 2 and CH 4 emissions during freezing stage were interrupted by a short emission peak. While N 2O uptake rate reduced with decreasing temperature. In the thawing stage, all the three greenhouse gases exhibited emission peaks. CO 2 were 159.83 mg m −2 h −1 (TQ) and 86.83 mg m −2 h −1 (SJ); CH 4 were 1.32 mg m −2 h −1 (TQ) and 4.07 mg m −2 h −1 (SJ); N 2O were 72.14 ug m −2 h −1 (TQ) and 22.15 ug m −2 h −1 (SJ). Meanwhile, N 2O transferred from sink into source. With temperature increase, the emission rate of CO 2 increased fast, while CH 4 and N 2O decreased. CO 2 emission during freezing-thawing periods was significantly correlated with soil temperature and CH 4 emission. Soil active organic carbon also played important roles in greenhouse gases emissions. Our study suggested that more greenhouse gases may release from wetlands into atmosphere in the context of global warming, and the potential release of CO 2 and N 2O during freezing-thawing periods was much higher in peatlands of permafrost zone. [ABSTRACT FROM AUTHOR]

Increased nitrogen (N) input to ecosystems could alter soil organic carbon (C) dynamics, but the effect still remains uncertain. To better understand the effect of N addition on soil organic C in wetland ecosystems, a field experiment was conducted in a seasonally inundated freshwater marsh, the Sanjiang Plain, Northeast China. In this study, litter production, soil total organic C (TOC) concentration, microbial biomass C (MBC), organic C mineralization, metabolic quotient ( qCO) and mineralization quotient ( qmC) in 0-15 cm depth were investigated after four consecutive years of N addition at four rates (CK, 0 g N m year; low, 6 g N m year; moderate, 12 g N m year; high, 24 g N m year). Four-year N addition increased litter production, and decreased soil organic C mineralization. In addition, soil TOC concentration and MBC generally increased at low and moderate N addition levels, but declined at high N addition level, whereas soil qCO and qmC showed a reverse trend. These results suggest that short-term N addition alters soil organic C dynamics in seasonally inundated freshwater marshes of Northeast China, and the effects vary with N fertilization rates. [ABSTRACT FROM AUTHOR]

Nitrogen deposition and global warming each have potential to alter soil carbon storage via changing decomposition, but combined effects of N addition and temperature on CO production in wetland soils are less studied. In this study, we conducted laboratory incubations to examine this problem using soil from a freshwater marsh in Sanjiang Plain, China. We found that N addition and temperature had a negative and positive effect on CO production, respectively. Despite low decomposition rates, heavy fractions had a notable contribution to CO production due to greater mass proportion in soil. Short-term combined effect of N addition and temperature on CO production was antagonistic. Based on greater N availability as N addition and temperature increasing, extra release of soil-derived N may further suppress CO production. We suggest that short-term soil CO production under simultaneous influence of temperature and N addition may be overestimated based on their single effects in this site. [ABSTRACT FROM AUTHOR]

A field control experiment was carried out to determine the influence of water table changes on soil CO, CH, and NO emissions in Calamagrostis angustifolia freshwater marsh in Northeast of China. The results showed that the water depth of 5 cm below the ground surface increased soil CO emission, but there was no significant influence of deeper water table on gas emission. CH emission was accelerated by deep standing water and approached the peak in the plant booming time. This suggests that root activity has influence on CH production. The result also demonstrated that both low water table level and inundated environment would inhibit NO emission. Comparing the total global warming potential of three gases under different conditions, it can be concluded that maintaining a comparatively steady water table near the soil surface can benefit soil carbon sequestration in the C. angustifolia marsh, and decrease of the greenhouse gases emissions to the atmosphere. [ABSTRACT FROM AUTHOR]

Soil management significantly affects the soil labile organic factors. Understanding carbon and nitrogen dynamics is extremely helpful in conducting research on active carbon and nitrogen components for different kinds of soil management. In this paper, we examined the changes in microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), dissolved organic carbon (DOC), and dissolved organic nitrogen (DON) to assess the effect and mechanisms of land types, organic input, soil respiration, microbial species, and vegetation recovery under Deyeuxia angustifolia freshwater marshes (DAMs) and recovered freshwater marsh (RFM) in the Sanjiang Plain, Northeast China. Identifying the relationship among the dynamics of labile carbon, nitrogen, and soil qualification mechanism using different land management practices is therefore important. Cultivation and land use affect intensely the DOC, DON, MBC, and MBN in the soil. After DAM soil tillage, the DOC, DON, MBC, and MBN at the surface of the agricultural soil layer declined significantly. In contrast, their recovery was significant in the RFM surface soil. A long time was needed for the concentration of cultivated soil total organic carbon and total nitrogen to be restored to the wetland level. The labile carbon and nitrogen fractions can reach a level similar to that of the wetland within a short time. Typical wetland ecosystem signs, such as vegetation, microbes, and animals, can be recovered by soil labile carbon and nitrogen fraction restoration. In this paper, the D. angustifolia biomass attained natural wetland level after 8 years, indicating that wetland soil labile fractions can support wetland eco-function in a short period of time (4 to 8 years) for reconstructed wetland under suitable environmental conditions. [ABSTRACT FROM AUTHOR]

Abstract: Nitrogen (N) is commonly a limited nutrient in wetland ecosystems. Nitrogen addition affects the ecosystem carbon (C) balance and alters soil C storage through soil chemical and biological changes. In the present study, the effects of N addition and vegetation removal after one growing season on soil properties were examined in a Calamagrostis angustifolia freshwater marsh in Northeast China. Specifically, available N (NH4 +–N and NO3 −–N), microbial biomass C (MBC), and dissolved organic C (DOC) concentrations in the soil were analyzed. In addition, activities of soil enzyme (β-glucosidase, invertase, and urease) were investigated. The results showed that N addition resulted in significant increase of NH4 +–N and NO3 −–N in both topsoil and subsoil, and vegetation removal enhanced these effects. Soil MBC concentrations increased after N addition and vegetation removal but DOC concentrations did not change significantly. As to soil enzyme activities, N addition stimulated the β-glucosidase activity in the topsoil and invertase and urease activities in both soil layers. Vegetation removal enhanced the effect of N addition on β-glucosidase and invertase activities but inhibited the effect on urease activity. These results suggested that N addition affects soil biochemical process indirectly through marshland vegetation. [Copyright &y& Elsevier]

To obtain genetic information and to evaluate the composition of T4-type bacteriophage (phage) communities in wetlands, environmental soil and water DNAs were obtained from two natural wetlands dominated by Carex lasiocarpa and Deyeuxia angustifolia plant species, and a neighboring paddy field in Sanjiang plain of northeast China. The biomarker gene of g23, which encodes the major capsid protein of T4-type phages, was amplified with primers MZIA1bis and MZIA6, and the PCR products were cloned and sequenced. In total, 96 and 50 different g23 clones were obtained from natural wetlands and a paddy field, respectively. A larger number of clones with low levels of identity to known sequences were found in water than in soil both in the natural wetlands and the paddy field, suggesting that many of T4-type phages in wetland water and paddy floodwater in Sanjiang plain are uncharacterized. Phylogenetic analyses showed that the g23 clones in natural wetlands, irrespective of water and soil, were distinctly different from those in marine waters, lake waters, and upland black soils, but were similar to those in paddy fields. The UniFrac analysis of g23 assemblages indicated that T4-type phage community compositions were different between soils and waters, and also were different between the natural wetlands and the paddy field. In general, the global analysis of g23 clone assemblages demonstrated that T4-type phage community compositions were different among natural wetlands, marines, lakes, paddy fields, and upland black soils. [ABSTRACT FROM AUTHOR]

Abstract: Soil organic carbon (SOC) in high latitude ecosystems is potentially vulnerable to global climate change. However, the distribution of SOC and total nitrogen (N) is still unknown for the boreal wetlands. In this study, we collected soil samples from different wetlands in the discontinuous permafrost zone of the Xiao Xing''an Mountains, northeastern China. Permafrost was only present in the bogs and fens in this zone. Soil C concentrations were significantly correlated with total N concentrations and bulk density (P <0.001). Wetland type, soil depth, and incidence of fire affected soil C and total N concentrations, suggesting that vegetation changes in wetlands could alter the soil C and nutrient sequestration processes under future global warming scenarios. However, soil C and total N storage in the 40cm depth was not significantly different between wetland types (P >0.05), suggesting that future global warming and vegetation change would not significantly affect soil C and total N storage in upper soil layers in wetlands. However, vegetation changes are likely to increase the depth of the permafrost active layer under permafrost degradation, release deep soil C, and add C to the atmosphere over the coming decades. [Copyright &y& Elsevier]

Abstract: Wetlands in mid-high latitude regions play a vital role in climate change, due to their high organic carbon density. Nonetheless, the stabilization of soil organic carbon (SOC) and its fractions in these regions is largely unknown. The objectives of this study were to examine the changes in SOC and its fractions along a latitudinal gradient and to analyze the influencing factors in the southern margin of the permafrost region on the Eurasian continent. Topsoil (0–20cm) was collected from five wetlands along a latitudinal gradient in Northeast China. We analyzed SOC and some labile fractions. Our results demonstrated that wetland SOC and its labile fractions concentration declined with decreasing latitude. The Permafrost regions had greater organic carbon content than the regions with seasonally frozen ground. The light fraction organic carbon and particulate organic carbon accounted for 5–83% and 21–32%, respectively, of the SOC and were particularly enriched in the permafrost region. Microbial biomass carbon and dissolved organic carbon showed a similar decreasing trend to that of SOC. At the same latitude, vegetation affected SOC stock and the dynamics of its labile fractions. Therefore, wetlands in mid-high latitudes contain a large carbon pool, and carbon stock varies with latitude. Although the labile fractions were higher in the permafrost region, their activities were lower, due to low temperature and poor nutrient status. Under global warming, the labile carbon pool may be mobilized and contribute to the greenhouse effect. Moreover, vegetation differences should be considered in obtaining an accurate carbon calculation. [Copyright &y& Elsevier]

Abstract: Northern wetlands are critically important to global change because of their role in modulating atmospheric concentrations of greenhouse gases, especially CO2 and CH4. At present, continuous observations for CO2 and CH4 fluxes from northern wetlands in Asia are still very limited. In this paper, two growing season measurements for CO2 flux by eddy covariance technique and CH4 flux by static chamber technique were conducted in 2004 and 2005, at a permanently inundated marsh in the Sanjiang Plain, northeastern China. The seasonal variations of CO2 exchange and CH4 flux and the environmental controls on them were investigated. During the growing seasons, large variations in net ecosystem CO2 exchange (NEE) and gross ecosystem productivity (GEP) were observed with the range of −4.0 to 2.2 (where negative exchange is a gain of carbon from the atmosphere) and 0–7.6gCm−2 d−1, respectively. Ecosystem respiration (RE) displayed relatively smooth seasonal pattern with the range of 0.8–4.2gCm−2 d−1. More than 70% of the total GEP was consumed by respiration, which resulted in a net CO2 uptake of 143±9.8 and 100±9.2gCm−2 for the marsh over the growing seasons of 2004 and 2005, respectively. A significant portion of the accumulated NEE-C was lost by CH4 emission during the growing seasons, indicating the great potential of CH4 emission from the inundated marsh. Air temperature and leaf area index jointly affected the seasonal variation of GEP and the seasonal dynamic of RE was mainly controlled by soil temperature and leaf area index. Soil temperature also exerted the dominant influence over variation of CH4 flux while no significant relationship was found between CH4 emission and water table level. The close relationships between carbon fluxes and temperature can provide insights into the response of marsh carbon exchange to a changing climate. Future long term flux measurements over the freshwater marsh ecosystems are undoubtedly necessary. [Copyright &y& Elsevier]

Natural wetlands are critically important to global change because of their role in modulating atmospheric concentrations of CO2, CH4, and N2O. One 4-year continuous observation was conducted to examine the exchanges of CH4 and N2O between three wetland ecosystems and the atmosphere as well as the ecosystem respiration in the Sanjiang Plain in Northeastern China. From 2002 to 2005, the mean annual budgets of CH4 and N2O, and ecosystem respiration were 39.40 ± 6.99 g C m−2 yr−1, 0.124 ± 0.05 g N m−2 yr−1, and 513.55 ± 8.58 g C m−2 yr−1 for permanently inundated wetland; 4.36 ± 1.79 g C m−2 yr−1, 0.11 ± 0.12 g N m−2 yr−1, and 880.50 ± 71.72 g C m−2 yr−1 for seasonally inundated wetland; and 0.21 ± 0.1 g C m−2 yr−1, 0.28 ± 0.11 g N m−2 yr−1, and 1212.83 ± 191.98 g C m−2 yr−1 for shrub swamp. The substantial interannual variation of gas fluxes was due to the significant climatic variability which underscores the importance of long-term continuous observations. The apparent seasonal pattern of gas emissions associated with a significant relationship of gas fluxes to air temperature implied the potential effect of global warming on greenhouse gas emissions from natural wetlands. The budgets of CH4 and N2O fluxes and ecosystem respiration were highly variable among three wetland types, which suggest the uncertainties in previous studies in which all kinds of natural wetlands were treated as one or two functional types. New classification of global natural wetlands in more detailed level is highly expected. [ABSTRACT FROM AUTHOR]

Abstract: The wetlands play an important role in carbon storage, especially at high latitudes, at which they store nearly one-third of global soil carbons. However, few studies have investigated the emissions of CO2, CH4 and N2O in the long-term, especially effects of freeze–thaw cycles on these gases emissions in freshwater marsh ecosystems. In this paper, we collected greenhouse gas emission data from a freshwater marsh area in China for 4 years, evaluated their release variables and speculated on their potential atmospheric impact. For this paper, we report on the CO2, CH4 and N2O emission rates recorded from June 2002 to November 2005 in the Sanjiang Plain of northeast China. We measured their interannual variations and fluctuations, as well as factors affecting their emissions, and estimated their regulation and freeze–thaw cycle impacts. Our results revealed obvious CO2 and CH4 emission fluctuations during the winter months, and during the freeze–thaw cycle, and a strong interannual variation during the growing season. Overall, we documented a close relationship between the CO2 and CH4 emissions, implicating some regulatory commonality. We determined that the marsh was a N2O sink during the winter, but a significant source of N2O during the freeze–thaw cycle as the temperature increased, especially in early summer. During the thaw–freeze period, the N2O levels were positively correlated with the water depth. Additionally, water depth greatly governed the interannual variation of the N2O emissions from the marshes during the thaw–freeze period. [Copyright &y& Elsevier]

Freshwater marshes could be a source of greenhouse gases emission because they contain large amounts of soil carbon and nitrogen. These emissions are strongly influenced by exogenous nitrogen. We investigate the effects of exogenous nitrogen on ecosystem respiration (CO2), CH4 and N2O emissions from freshwater marshes in situ in the Sanjiang Plain Northeast of China during the growing seasons of 2004 and 2005, using a field fertilizer experiment and the static opaque chamber/GC techniques. The results show that there were no significant differences in patterns of seasonal variations of CO2 and CH4 among the fertilizer and non-fertilizer treatments, but the seasonal patterns of N2O emission were significantly influenced by the exogenous nitrogen. Seasonal averages of the CO2 flux from non-fertilizer and fertilizer were 987.74 and 1,344.35 mg m −2 h −1, respectively, in 2004, and 898.59 and 2,154.17 mg m −2 h −1, respectively, in 2005. And the CH4 from the control and fertilizer treatments were 6.05 and 13.56 mg m −2 h −1 and 0.72 and 1.88 mg m −2 h −1, respectively, in 2004 and 2005. The difference of N2O flux between the fertilizer and non-fertilizer treatments is also significant either in 2004 and 2005. On the time scale of 20-, 100-, and 500-year periods, the integrated global warming potential (GWP) of CO2 + CH4 + N2O released during the two growing seasons for the treatment of fertilizer was 97, 94 and 89%, respectively, higher than that for the control, which suggested that the nitrogen fertilizer can enhance the GWP of the CH4 and N2O either in long time or short time scale. [ABSTRACT FROM AUTHOR]