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1.
The responses of soil-atmosphere carbon (C) exchange fluxes to growing atmospheric nitrogen (N) deposition are controversial, leading to large uncertainty in the estimated C sink of global forest ecosystems experiencing substantial N inputs. However, it is challenging to quantify critical load of N input for the alteration of the soil C fluxes, and what factors controlled the changes in soil CO2 and CH4 fluxes under N enrichment. Nine levels of urea addition experiment (0, 10, 20, 40, 60, 80, 100, 120, 140 kg N ha−1 yr−1) were conducted in the needle-broadleaved mixed forest in Changbai Mountain, Northeast China. Soil CO2 and CH4 fluxes were monitored weekly using the static chamber and gas chromatograph technique. Environmental variables (soil temperature and moisture in the 0–10 cm depth) and dissolved N (NH4+-N, NO3−-N, total dissolved N (TDN), and dissolved organic N (DON)) in the organic layer and the 0–10 cm mineral soil layer were simultaneously measured. High rates of N addition (≥60 kg N ha−1 yr−1) significantly increased soil NO3−-N contents in the organic layer and the mineral layer by 120%-180% and 56.4%-84.6%, respectively. However, N application did not lead to a significant accumulation of soil NH4+-N contents in the two soil layers except for a few treatments. N addition at a low rate of 10 kg N ha−1 yr−1 significantly stimulated, whereas high rate of N addition (140 kg N ha−1 yr−1) significantly inhibited soil CO2 emission and CH4 uptake. Significant negative relationships were observed between changes in soil CO2 emission and CH4 uptake and changes in soil NO3−-N and moisture contents under N enrichment. These results suggest that soil nitrification and NO3−-N accumulation could be important regulators of soil CO2 emission and CH4 uptake in the temperate needle-broadleaved mixed forest. The nonlinear responses to exogenous N inputs and the critical level of N in terms of soil C fluxes should be considered in the ecological process models and ecosystem management. 相似文献
2.
氮素类型和剂量对寒温带针叶林土壤N2O排放的影响 总被引:1,自引:0,他引:1
大气氮沉降输入会增加森林生态系统氮素有效性,进而改变土壤N_2O产生与排放,然而有关不同氮素离子(氧化态NO_3~--N与还原态NH_4~+-N)沉降对土壤N_2O排放的影响知之甚少。以大兴安岭寒温带针叶林为研究对象,构建了3种类型(NH_4Cl、KNO_3、NH_4NO_3)和4个施氮水平(0、10、20、40 kg N hm~(-2)a~(-1))的增氮控制试验,利用流动化学分析仪和静态箱-气相色谱法4次/月测定凋落物层和矿质层土壤无机氮含量、土壤-大气界面N_2O净交换通量以及相关环境因子,分析施氮类型和剂量对土壤氮素有效性、土壤N_2O通量的影响探讨氮素富集条件下土壤N_2O通量的环境驱动机制。结果表明:施氮类型和剂量均显著影响土壤无机氮含量,土壤NH_4~+-N的积累效应显著高于NO_3~--N。施氮一致增加寒温带针叶林土壤N_2O排放,NH_4NO_3促进效应最为明显,增幅为442%-677%,高于全球平均水平(134%)。土壤N_2O通量与土壤温度、凋落物层NH_4~+-N含量正相关,且随着施氮水平增加而增加。结果表明大气氮沉降短期内不会导致寒温带针叶林土壤NO_3~--N大量流失,但会显著促进土壤N_2O的排放。此外,外源性NH_4~+和NO_3~-输入对土壤N_2O排放的促进作用具有协同效应,在未来森林生态系统氮循环和氮平衡研究中应该区分对待。 相似文献
3.
S. Zaehle 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2013,368(1621)
Interactions between the terrestrial nitrogen (N) and carbon (C) cycles shape the response of ecosystems to global change. However, the global distribution of nitrogen availability and its importance in global biogeochemistry and biogeochemical interactions with the climate system remain uncertain. Based on projections of a terrestrial biosphere model scaling ecological understanding of nitrogen–carbon cycle interactions to global scales, anthropogenic nitrogen additions since 1860 are estimated to have enriched the terrestrial biosphere by 1.3 Pg N, supporting the sequestration of 11.2 Pg C. Over the same time period, CO2 fertilization has increased terrestrial carbon storage by 134.0 Pg C, increasing the terrestrial nitrogen stock by 1.2 Pg N. In 2001–2010, terrestrial ecosystems sequestered an estimated total of 27 Tg N yr−1 (1.9 Pg C yr−1), of which 10 Tg N yr−1 (0.2 Pg C yr−1) are due to anthropogenic nitrogen deposition. Nitrogen availability already limits terrestrial carbon sequestration in the boreal and temperate zone, and will constrain future carbon sequestration in response to CO2 fertilization (regionally by up to 70% compared with an estimate without considering nitrogen–carbon interactions). This reduced terrestrial carbon uptake will probably dominate the role of the terrestrial nitrogen cycle in the climate system, as it accelerates the accumulation of anthropogenic CO2 in the atmosphere. However, increases of N2O emissions owing to anthropogenic nitrogen and climate change (at a rate of approx. 0.5 Tg N yr−1 per 1°C degree climate warming) will add an important long-term climate forcing. 相似文献
4.
A new estimation of global soil greenhouse gas fluxes using a simple data-oriented model 总被引:2,自引:0,他引:2
S Hashimoto 《PloS one》2012,7(8):e41962
Soil greenhouse gas fluxes (particularly CO2, CH4, and N2O) play important roles in climate change. However, despite the importance of these soil greenhouse gases, the number of reports on global soil greenhouse gas fluxes is limited. Here, new estimates are presented for global soil CO2 emission (total soil respiration), CH4 uptake, and N2O emission fluxes, using a simple data-oriented model. The estimated global fluxes for CO2 emission, CH4 uptake, and N2O emission were 78 Pg C yr−1 (Monte Carlo 95% confidence interval, 64–95 Pg C yr−1), 18 Tg C yr−1 (11–23 Tg C yr−1), and 4.4 Tg N yr−1 (1.4–11.1 Tg N yr−1), respectively. Tropical regions were the largest contributor of all of the gases, particularly the CO2 and N2O fluxes. The soil CO2 and N2O fluxes had more pronounced seasonal patterns than the soil CH4 flux. The collected estimates, including both the previous and the present estimates, demonstrate that the means of the best estimates from each study were 79 Pg C yr−1 (291 Pg CO2 yr−1; coefficient of variation, CV = 13%, N = 6) for CO2, 21 Tg C yr−1 (29 Tg CH4 yr−1; CV = 24%, N = 24) for CH4, and 7.8 Tg N yr−1 (12.2 Tg N2O yr−1; CV = 38%, N = 11) for N2O. For N2O, the mean of the estimates that was calculated by excluding the earliest two estimates was 6.6 Tg N yr−1 (10.4 Tg N2O yr−1; CV = 22%, N = 9). The reported estimates vary and have large degrees of uncertainty but their overall magnitudes are in general agreement. To further minimize the uncertainty of soil greenhouse gas flux estimates, it is necessary to build global databases and identify key processes in describing global soil greenhouse gas fluxes. 相似文献
5.
E. D. SCHULZE P. CIAIS S. LUYSSAERT M. SCHRUMPF I. A. JANSSENS B. THIRUCHITTAMPALAM J. THELOKE M. SAURAT S. BRINGEZU J. LELIEVELD A. LOHILA C. REBMANN M. JUNG D. BASTVIKEN G. ABRIL G. GRASSI A. LEIP A. FREIBAUER W. KUTSCH A. DON J. NIESCHULZE A. BÖRNER J. H. GASH A. J. DOLMAN 《Global Change Biology》2010,16(5):1451-1469
Overviewing the European carbon (C), greenhouse gas (GHG), and non‐GHG fluxes, gross primary productivity (GPP) is about 9.3 Pg yr?1, and fossil fuel imports are 1.6 Pg yr?1. GPP is about 1.25% of solar radiation, containing about 360 × 1018 J energy – five times the energy content of annual fossil fuel use. Net primary production (NPP) is 50%, terrestrial net biome productivity, NBP, 3%, and the net GHG balance, NGB, 0.3% of GPP. Human harvest uses 20% of NPP or 10% of GPP, or alternatively 1‰ of solar radiation after accounting for the inherent cost of agriculture and forestry, for production of pesticides and fertilizer, the return of organic fertilizer, and for the C equivalent cost of GHG emissions. C equivalents are defined on a global warming potential with a 100‐year time horizon. The equivalent of about 2.4% of the mineral fertilizer input is emitted as N2O. Agricultural emissions to the atmosphere are about 40% of total methane, 60% of total NO‐N, 70% of total N2O‐N, and 95% of total NH3‐N emissions of Europe. European soils are a net C sink (114 Tg yr?1), but considering the emissions of GHGs, soils are a source of about 26 Tg CO2 C‐equivalent yr?1. Forest, grassland and sediment C sinks are offset by GHG emissions from croplands, peatlands and inland waters. Non‐GHGs (NH3, NOx) interact significantly with the GHG and the C cycle through ammonium nitrate aerosols and dry deposition. Wet deposition of nitrogen (N) supports about 50% of forest timber growth. Land use change is regionally important. The absolute flux values total about 50 Tg C yr?1. Nevertheless, for the European trace‐gas balance, land‐use intensity is more important than land‐use change. This study shows that emissions of GHGs and non‐GHGs significantly distort the C cycle and eliminate apparent C sinks. 相似文献
6.
Shuqi Xiao Chao Wang Kai Yu Genyuan Liu Shuang Wu Jinyang Wang Shuli Niu Jianwen Zou Shuwei Liu 《Global Change Biology》2023,29(20):5829-5849
Despite the increasing impact of atmospheric nitrogen (N) deposition on terrestrial greenhouse gas (GHG) budget, through driving both the net atmospheric CO2 exchange and the emission or uptake of non-CO2 GHGs (CH4 and N2O), few studies have assessed the climatic impact of forests and grasslands under N deposition globally based on different bottom-up approaches. Here, we quantify the effects of N deposition on biomass C increment, soil organic C (SOC), CH4 and N2O fluxes and, ultimately, the net ecosystem GHG balance of forests and grasslands using a global comprehensive dataset. We showed that N addition significantly increased plant C uptake (net primary production) in forests and grasslands, to a larger extent for the aboveground C (aboveground net primary production), whereas it only caused a small or insignificant enhancement of SOC pool in both upland systems. Nitrogen addition had no significant effect on soil heterotrophic respiration (RH) in both forests and grasslands, while a significant N-induced increase in soil CO2 fluxes (RS, soil respiration) was observed in grasslands. Nitrogen addition significantly stimulated soil N2O fluxes in forests (76%), to a larger extent in grasslands (87%), but showed a consistent trend to decrease soil uptake of CH4, suggesting a declined sink capacity of forests and grasslands for atmospheric CH4 under N enrichment. Overall, the net GHG balance estimated by the net ecosystem production-based method (forest, 1.28 Pg CO2-eq year−1 vs. grassland, 0.58 Pg CO2-eq year−1) was greater than those estimated using the SOC-based method (forest, 0.32 Pg CO2-eq year−1 vs. grassland, 0.18 Pg CO2-eq year−1) caused by N addition. Our findings revealed that the enhanced soil C sequestration by N addition in global forests and grasslands could be only marginally offset (1.5%–4.8%) by the combined effects of its stimulation of N2O emissions together with the reduced soil uptake of CH4. 相似文献
7.
The effects of inorganic nutrient (ammonium [NH4 + ] and nitrate [NO3 − ]) and amino acid (glutamate [glu] and glutamine [gln]) additions on rates of N2 fixation, N uptake, glutamine synthetase (GS) activity, and concentrations of intracellular pools of gln and glu were examined in natural and cultured populations of Trichodesmium. Additions of 1 μM glu, gln, NO3 − , or NH4 + did not affect short-term rates of N2 fixation. This may be an important factor that allows for continued N2 fixation in oligotrophic areas where recycling processes are active. N2 fixation rates decreased when nutrients were supplied at higher concentrations (e.g. 10 μM). Uptake of combined N (NH4 + , NO3 − , and amino acids) by Trichodesmium was stimulated by increased concentrations. For NO3 − , proportional increases in NO3 − uptake and decreases in N2 fixation were observed when additions were made to cultures before the onset of the light period. GS activity did not change much in response to the addition of NH4 + , NO3 − , glu, or gln. GS is necessary for N metabolism, and the bulk of this enzyme pool may be conserved. Intracellular pools of glu and gln varied in response to 10 μM additions of NH4 + , glu, or gln. Cells incubated with NH4 + became depleted in intracellular glu and enriched with intracellular gln. The increase in the gln/glu ratio corresponded to a decrease in the rate of N2 fixation. Although the gln/glu ratio decreased in cells exposed to the amino acids, there was only a corresponding decrease in N2 fixation after the gln addition. The results presented here suggest that combined N concentrations on the order of 1 μM do not affect rates of N2 fixation and metabolism, although higher concentrations (e.g. 10 μM) can. Moreover, these effects are exerted through products of NH4 + assimilation rather than exogenous N, as has been suggested for other species. These results may help explain how cultures of Trichodesmium are able to simultaneously fix N2 and take up NH4 + and how natural populations continue to fix N2 once combined N concentrations increase within a bloom. 相似文献
8.
Biological soil crusts composed of cyanobacteria, green algae, bryophytes, and lichens colonize soils in arid and semiarid
ecosystems worldwide and are responsible for significant N input to the soils of these ecosystems. Soil crusts also colonize
active sand dunes in more humid regions, but studies of structure and function of such sand dune crusts are lacking. We identified
the cyanobacterial, algal, and bryophytic constituents and N production and leachates of biological soil crusts that colonize
beach dunes at the Indiana Dunes National Lakeshore along southern Lake Michigan in Indiana, USA. To determine the role of
these crusts in this system, we conducted a greenhouse experiment in which intact soil cores with biological crusts were subjected
to artificial rainfall over a full growing season. The volume and N content of leachate from the cores were quantified in
relation to degree of crust development, taxonomic composition, rainfall volume and intensity, light intensity, and the presence
of plant litter. Net N throughput significantly exceeded N inputs to cores in rainwater. Net N outputs from crusts to subsurface
soil ranged from 0. 01 to 0.19 g NH
4
+
-N m−2 yr−1 and 0.01 to 0.61 g NO
3
–
N m−2 yr−1. Thus, total inorganic N inputs associated with biological soil crusts ranged from 0.02 g N m−2 yr−1 to 0.8 g N m−2 yr−1. High volume (≥2 cm) rainfall resulted in more N leaching than low volume events, and plant litter added over the surface
of crusted soil cores significantly increased the amount of N in leachate. Exploratory path analysis revealed direct and indirect
linkages among environmental factors, crust development, and crust composition in regulating the throughput of H2O and N from these intact soil cores. Biological soil crusts at this site, combined with other properties of the soil surface,
substantially increase N inputs to this water- and nutrient-limited sand dune ecosystem. 相似文献
9.
Shuang Wu Cheng Ji Yi Sun Yaguo Jin Shuqing Li Zhaofu Li Jianwen Zou 《Global Change Biology》2017,23(6):2520-2532
Soils are among the important sources of atmospheric nitric oxide (NO) and nitrous oxide (N2O), acting as a critical role in atmospheric chemistry. Updated data derived from 114 peer‐reviewed publications with 520 field measurements were synthesized using meta‐analysis procedure to examine the N fertilizer‐induced soil NO and the combined NO+N2O emissions across global soils. Besides factors identified in earlier reviews, additional factors responsible for NO fluxes were fertilizer type, soil C/N ratio, crop residue incorporation, tillage, atmospheric carbon dioxide concentration, drought and biomass burning. When averaged across all measurements, soil NO‐N fluxes were estimated to be 4.06 kg ha?1 yr?1, with the greatest (9.75 kg ha?1 yr?1) in vegetable croplands and the lowest (0.11 kg ha?1 yr?1) in rice paddies. Soil NO emissions were more enhanced by synthetic N fertilizer (+38%), relative to organic (+20%) or mixed N (+18%) sources. Compared with synthetic N fertilizer alone, synthetic N fertilizer combined with nitrification inhibitors substantially reduced soil NO emissions by 81%. The global mean direct emission factors of N fertilizer for NO (EFNO) and combined NO+N2O (EFc) were estimated to be 1.16% and 2.58%, with 95% confidence intervals of 0.71–1.61% and 1.81–3.35%, respectively. Forests had the greatest EFNO (2.39%). Within the croplands, the EFNO (1.71%) and EFc (4.13%) were the greatest in vegetable cropping fields. Among different chemical N fertilizer varieties, ammonium nitrate had the greatest EFNO (2.93%) and EFc (5.97%). Some options such as organic instead of synthetic N fertilizer, decreasing N fertilizer input rate, nitrification inhibitor and low irrigation frequency could be adopted to mitigate soil NO emissions. More field measurements over multiyears are highly needed to minimize the estimate uncertainties and mitigate soil NO emissions, particularly in forests and vegetable croplands. 相似文献
10.
Nitrogen addition reduces soil respiration in a mature tropical forest in southern China 总被引:10,自引:0,他引:10
JIANGMING MO WEI ZHANG WEIXING ZHU† PER GUNDERSEN‡ YUNTING FANG DEJUN LI HUI WANG 《Global Change Biology》2008,14(2):403-412
Response of soil respiration (CO2 emission) to simulated nitrogen (N) deposition in a mature tropical forest in southern China was studied from October 2005 to September 2006. The objective was to test the hypothesis that N addition would reduce soil respiration in N saturated tropical forests. Static chamber and gas chromatography techniques were used to quantify the soil respiration, following four‐levels of N treatments (Control, no N addition; Low‐N, 5 g N m?2 yr?1; Medium‐N, 10 g N m?2 yr?1; and High‐N, 15 g N m?2 yr?1 experimental inputs), which had been applied for 26 months before and continued throughout the respiration measurement period. Results showed that soil respiration exhibited a strong seasonal pattern, with the highest rates found in the warm and wet growing season (April–September) and the lowest rates in the dry dormant season (December–February). Soil respiration rates showed a significant positive exponential relationship with soil temperature, whereas soil moisture only affect soil respiration at dry conditions in the dormant season. Annual accumulative soil respiration was 601±30 g CO2‐C m?2 yr?1 in the Controls. Annual mean soil respiration rate in the Control, Low‐N and Medium‐N treatments (69±3, 72±3 and 63±1 mg CO2‐C m?2 h?1, respectively) did not differ significantly, whereas it was 14% lower in the High‐N treatment (58±3 mg CO2‐C m?2 h?1) compared with the Control treatment, also the temperature sensitivity of respiration, Q10 was reduced from 2.6 in the Control with 2.2 in the High‐N treatment. The decrease in soil respiration occurred in the warm and wet growing season and were correlated with a decrease in soil microbial activities and in fine root biomass in the N‐treated plots. Our results suggest that response of soil respiration to atmospheric N deposition in tropical forests is a decline, but it may vary depending on the rate of N deposition. 相似文献
11.
Responses of terrestrial nitrogen pools and dynamics to different patterns of freeze‐thaw cycle: A meta‐analysis
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Decai Gao Lei Zhang Jun Liu Bo Peng Zhenzhen Fan Weiwei Dai Ping Jiang Edith Bai 《Global Change Biology》2018,24(6):2377-2389
Altered freeze‐thaw cycle (FTC) patterns due to global climate change may affect nitrogen (N) cycling in terrestrial ecosystems. However, the general responses of soil N pools and fluxes to different FTC patterns are still poorly understood. Here, we compiled data of 1519 observations from 63 studies and conducted a meta‐analysis of the responses of 17 variables involved in terrestrial N pools and fluxes to FTC. Results showed that under FTC treatment, soil NH4+, NO3?, NO3? leaching, and N2O emission significantly increased by 18.5%, 18.3%, 66.9%, and 144.9%, respectively; and soil total N (TN) and microbial biomass N (MBN) significantly decreased by 26.2% and 4.7%, respectively; while net N mineralization or nitrification rates did not change. Temperate and cropland ecosystems with relatively high soil nutrient contents were more responsive to FTC than alpine and arctic tundra ecosystems with rapid microbial acclimation. Therefore, altered FTC patterns (such as increased duration of FTC, temperature of freeze, amplitude of freeze, and frequency of FTC) due to global climate warming would enhance the release of inorganic N and the losses of N via leaching and N2O emissions. Results of this meta‐analysis help better understand the responses of N cycling to FTC and the relationships between FTC patterns and N pools and N fluxes. 相似文献
12.
Contemporary carbon balance and late Holocene carbon accumulation in a northern peatland 总被引:2,自引:0,他引:2
NIGEL T. ROULET †‡ PETER M. LAFLEUR§ PIERRE J. H. RICHARD¶ ‡ TIM R. MOORE ‡ ELYN R. HUMPHREYS JILL BUBIER 《Global Change Biology》2007,13(2):397-411
Northern peatlands contain up to 25% of the world's soil carbon (C) and have an estimated annual exchange of CO2‐C with the atmosphere of 0.1–0.5 Pg yr−1 and of CH4‐C of 10–25 Tg yr−1. Despite this overall importance to the global C cycle, there have been few, if any, complete multiyear annual C balances for these ecosystems. We report a 6‐year balance computed from continuous net ecosystem CO2 exchange (NEE), regular instantaneous measurements of methane (CH4) emissions, and export of dissolved organic C (DOC) from a northern ombrotrophic bog. From these observations, we have constructed complete seasonal and annual C balances, examined their seasonal and interannual variability, and compared the mean 6‐year contemporary C exchange with the apparent C accumulation for the last 3000 years obtained from C density and age‐depth profiles from two peat cores. The 6‐year mean NEE‐C and CH4‐C exchange, and net DOC loss are −40.2±40.5 (±1 SD), 3.7±0.5, and 14.9±3.1 g m−2 yr−1, giving a 6‐year mean balance of −21.5±39.0 g m−2 yr−1 (where positive exchange is a loss of C from the ecosystem). NEE had the largest magnitude and variability of the components of the C balance, but DOC and CH4 had similar proportional variabilities and their inclusion is essential to resolve the C balance. There are large interseasonal and interannual ranges to the exchanges due to variations in climatic conditions. We estimate from the largest and smallest seasonal exchanges, quasi‐maximum limits of the annual C balance between 50 and −105 g m−2 yr−1. The net C accumulation rate obtained from the two peatland cores for the interval 400–3000 bp (samples from the anoxic layer only) were 21.9±2.8 and 14.0±37.6 g m−2 yr−1, which are not significantly different from the 6‐year mean contemporary exchange. 相似文献
13.
Nitrous oxide (N2O) in soils is produced through nitrification and denitrification. The N2O produced is considered as a nitrogen (N) loss because it will most likely escape from the soil to the atmosphere as N2O or N2. Aim of the study was to quantify N2O production in grassland on peat soils in relation to N input and to determine the relative contribution of nitrification and denitrification to N2O production. Measurements were carried out on a weekly basis in 2 grasslands on peat soil (Peat I and Peat II) for 2 years (1993 and 1994) using intact soil core incubations. In additional experiments distinction between N2O from nitrification and denitrification was made by use of the gaseous nitrification inhibitor methyl fluoride (CH3F).Nitrous oxide production over the 2 year period was on average 34 kg N ha-1 yr-1 for mown treatments that received no N fertiliser and 44 kg N ha-1 yr-1 for mown and N fertilised treatments. Grazing by dairy cattle on Peat I caused additional N2O production to reach 81 kg N ha-1 yr-1. The sub soil (20–40 cm) contributed 25 to 40% of the total N2O production in the 0–40 cm layer. The N2O production:denitrification ratio was on average about 1 in the top soil and 2 in the sub soil indicating that N2O production through nitrification was important. Experiments showed that when ratios were larger than l, nitrification was the major source of N2O. In conclusion, N2O production is a significant N loss mechanism in grassland on peat soil with nitrification as an important N2O producing process. 相似文献
14.
The influence of forest stand age in a Picea sitchensis plantation on (1) soil fluxes of three greenhouse gases (GHGs – CO2, CH4 and N2O) and (2) overall net ecosystem global warming potential (GWP), was investigated in a 2‐year study. The objective was to isolate the effect of forest stand age on soil edaphic characteristics (temperature, water table and volumetric moisture) and the consequent influence of these characteristics on the GHG fluxes. Fluxes were measured in a chronosequence in Harwood, England, with sites comprising 30‐ and 20‐year‐old second rotation forest and a site clearfelled (CF) some 18 months before measurement. Adjoining unforested grassland (UN) acted as a control. Comparisons were made between flux data, soil temperature and moisture data and, at the 30‐year‐old and CF sites, eddy covariance data for net ecosystem carbon (C) exchange (NEE). The main findings were: firstly, integrated CO2 efflux was the dominant influence on the GHG budget, contributing 93–94% of the total GHG flux across the chronosequence compared with 6–7% from CH4 and N2O combined. Secondly, there were clear links between the trends in edaphic factors as the forest matured, or after clearfelling, and the emission of GHGs. In the chronosequence sites, annual fluxes of CO2 were lower at the 20‐year‐old (20y) site than at the 30‐year‐old (30y) and CF sites, with soil temperature the dominant control. CH4 efflux was highest at the CF site, with peak flux 491±54.5 μg m−2 h−1 and maximum annual flux 18.0±1.1 kg CH4 ha−1 yr−1. No consistent uptake of CH4 was noted at any site. A linear relationship was found between log CH4 flux and the closeness of the water table to the soil surface across all sites. N2O efflux was highest in the 30y site, reaching 108±38.3 μg N2O‐N m−2 h−1 (171 μg N2O m−2 h−1) in midsummer and a maximum annual flux of 4.7±1.2 kg N2O ha−1 yr−1 in 2001. Automatic chamber data showed a positive exponential relationship between N2O flux and soil temperature at this site. The relationship between N2O emission and soil volumetric moisture indicated an optimum moisture content for N2O flux of 40–50% by volume. The relationship between C : N ratio data and integrated N2O flux was consistent with a pattern previously noted across temperate and boreal forest soils. 相似文献
15.
In two mountain ecosystems at the Alptal research site in central Switzerland, pulses of 15NO3 and 15NH4 were separately applied to trace deposited inorganic N. One forested and one litter meadow catchment, each approximately
1600 m2, were delimited by trenches in the Gleysols. K15NO3 was applied weekly or fortnightly over one year with a backpack sprayer, thus labelling the atmospheric nitrate deposition.
After the sampling and a one-year break, 15NH4Cl was applied as a second one-year pulse, followed by a second sampling campaign. Trees (needles, branches and bole wood),
ground vegetation, litter layer and soil (LF, A and B horizon) were sampled at the end of each labelling period. Extractable
inorganic N, microbial N, and immobilised soil N were analysed in the LF and A horizons. During the whole labelling period,
the runoff water was sampled as well. Most of the added tracer remained in both ecosystems. More NO3− than NH4+ tracer was retained, especially in the forest. The highest recovery was in the soil, mainly in the organic horizon, and in
the ground vegetation, especially in the mosses. Event-based runoff analyses showed an immediate response of 15NO3− in runoff, with sharp 15N peaks corresponding to discharge peaks. NO3− leaching showed a clear seasonal pattern, being highest in spring during snowmelt. The high capacity of N retention in these
ecosystems leads to the assumption that deposited N accumulates in the soil organic matter, causing a progressive decline
of its C:N ratio. 相似文献
16.
Guo-Jiao Yang Carly Stevens Zi-Jia Zhang Xiao-Tao Lü Xing-Guo Han 《Global Change Biology》2023,29(16):4586-4594
Identifying the thresholds for the positive responses of total net primary productivity (NPP) to nitrogen (N) enrichment is an essential prerequisite for predicting the benefits of N deposition on ecosystem carbon sequestration. However, the responses of below-ground NPP (BNPP) to N enrichment are unknown in many ecosystems, which limits our ability to understand the carbon cycling under the scenario of increasing N availability. We examined the changes in above-ground NPP (ANPP), BNPP, and NPP of a temperate meadow steppe across a wide-ranging N addition gradient (0, 2, 5, 10, 20, and 50 g N m−2 year−1) during 5 years. Both ANPP and NPP increased nonlinearly with N addition rates. The N saturation threshold for ANPP (TA) and NPP (TN) was at the rate of 13.11 and 6.70 g N m−2 year−1, respectively. BNPP decreased with increasing N addition when N addition rates ˃5 g N m−2 year−1, resulting in much lower TN than TA. Soil N enrichment played a key role in driving the negative impacts of high N addition rates on BNPP, and consequently on the earlier occurrence of N saturation threshold for NPP. Our results highlight the negative effects of soil N enrichment on NPP in natural grasslands super-saturated with N. Furthermore, by considering ANPP and BNPP simultaneously, our results indicate that previous findings from above-ground might have over-estimated the positive effects of N deposition on primary productivity. 相似文献
17.
MATS NILSSON JÖRGEN SAGERFORS ISHI BUFFAM HJALMAR LAUDON TOBIAS ERIKSSON ACHIM GRELLE LEIF KLEMEDTSSON PER WESLIEN ANDERS LINDROTH 《Global Change Biology》2008,14(10):2317-2332
Based on theories of mire development and responses to a changing climate, the current role of mires as a net carbon sink has been questioned. A rigorous evaluation of the current net C-exchange in mires requires measurements of all relevant fluxes. Estimates of annual total carbon budgets in mires are still very limited. Here, we present a full carbon budget over 2 years for a boreal minerogenic oligotrophic mire in northern Sweden (64°11′N, 19°33′E). Data on the following fluxes were collected: land–atmosphere CO2 exchange (continuous Eddy covariance measurements) and CH4 exchange (static chambers during the snow free period); TOC (total organic carbon) in precipitation; loss of TOC, dissolved inorganic carbon (DIC) and CH4 through stream water runoff (continuous discharge measurements and regular C-concentration measurements). The mire constituted a net sink of 27±3.4 (±SD) g C m−2 yr−1 during 2004 and 20±3.4 g C m−2 yr−1 during 2005. This could be partitioned into an annual surface–atmosphere CO2 net uptake of 55±1.9 g C m−2 yr−1 during 2004 and 48±1.6 g C m−2 yr−1 during 2005. The annual NEE was further separated into a net uptake season, with an uptake of 92 g C m−2 yr−1 during 2004 and 86 g C m−2 yr−1 during 2005, and a net loss season with a loss of 37 g C m−2 yr−1 during 2004 and 38 g C m−2 yr−1 during 2005. Of the annual net CO2-C uptake, 37% and 31% was lost through runoff (with runoff TOC>DIC≫CH4) and 16% and 29% through methane emission during 2004 and 2005, respectively. This mire is still a significant C-sink, with carbon accumulation rates comparable to the long-term Holocene C-accumulation, and higher than the C-accumulation during the late Holocene in the region. 相似文献
18.
Changes in nitrogen cycling and retention processes in soils under spruce forests along a nitrogen enrichment gradient in Germany 总被引:5,自引:0,他引:5
MARIFE D. CORRE RAINER BRUMME EDZO VELDKAMP FRIEDRICH O. BEESE 《Global Change Biology》2007,13(7):1509-1527
A network of long-term monitoring sites on nitrogen (N) input and output of forests across Germany showed that a number of Germany's forests are subject to or are experiencing N saturation and that spruce (Picea abies) stands have high risk. Our study was aimed at (1) quantifying the changes in gross rates of microbial N cycling and retention processes in forest soils along an N enrichment gradient and (2) relating the changes in soil N dynamics to N losses. We selected spruce sites representing an N enrichment gradient (indicated by leaching : throughfall N ratios) ranging from 0.04–0.13 (low N),≤0.26 (intermediate N enrichment) to≥0.42 (highly N enriched). To our knowledge, our study is the first to report on mechanistic changes in gross rates of soil N cycling and abiotic NO3− retention under ambient N enrichment gradient. Gross N mineralization, NH4+ immobilization, gross nitrification, and NO3− immobilization rates increased up to intermediate N enrichment level and somewhat decreased at highly N-enriched condition. The turnover rates of NH4+ and microbial N pools increased while the turnover rates of the NO3− pool decreased across the N enrichment gradient. Abiotic immobilization of NH4+ did not differ across sites and was lower than that of NO3−. Abiotic NO3− immobilization decreased across the N enrichment gradient. Microbial assimilation and turnover appeared to contribute largely to the retention of NH4+. The increasing NO3− deposition and decreasing turnover rates of the NO3− pool, combined with decreasing abiotic NO3− retention, possibly contributed to increasing NO3− leaching and gaseous emissions across the N enrichment gradient. The empirical relationships of changes in microbial N cycling across the N enrichment gradient may be integrated in models used to predict responses of forest ecosystems (e.g. spruce) to increasing N deposition. 相似文献
19.
William B. Bowden 《Biogeochemistry》1986,2(3):249-279
There is increasing interest in the importance of nitrogen gas emissions from natural (non-agricultural) ecosystems with respect to local as well as global nitrogen budgets and with respect to the effects of nitrogen oxides on atmospheric ozone levels and global warming. The volatile forms of nitrogen of common interest are ammonia (NH3), nitrous oxide, (N2O), dinitrogen (N2), and NOx (principally NO + NO2). It is often difficult to attribute emissions of these compounds from soils to a single process because they are produced by a variety of common biogeochemical mechanisms. Although environmental conditions in the soil often appear to favor nitrogen gas emissions, the potential nitrogen gas emission rate from undisturbed ecosystems is rarely approached. The best estimates to date suggest that nitrogen gas emission rates from undisturbed ecosystems typically range from > 1 to perhaps 10 or 20 kg N ha-1 yr-1. Under certain conditions, however, emission rates may be much higher. For example, excreta from animals in grasslands may elevate ammonia volatilization up to 100 kg N ha-1 yr-1 depending on grazer density; tidal input of nutrients to coastal wetlands may support denitrification rates of several hundred kg N ha-1 yr-1 . Excepting such cases, gaseous nitrogen losses are probably a small component of the local nitrogen budget in most undisturbed ecosystems. However, emissions from undisturbed soils are an important component of the global source strengths for (N2O + N2), N2O and NOx (50%, 21%, and 10% respectively). Emission rates of N2O from natural ecosystems are higher than assumed previously by perhaps 10 times. Large-scale disturbance may have a stimulatory effect on nitrogen emission rates which could have important effects on global nitrogen budgets. There is a need for more sophisticated methods to account for natural temporal and spatial variations of emissions rates, to more accurately and precisely assess their global source strengths. 相似文献
20.
Martin Gauder Klaus Butterbach‐Bahl Simone Graeff‐Hönninger Wilhelm Claupein Regina Wiegel 《Global Change Biology Bioenergy》2012,4(3):289-301
Willow coppice, energy maize and Miscanthus were evaluated regarding their soil‐derived trace gas emission potential involving a nonfertilized and a crop‐adapted slow‐release nitrogen (N) fertilizer scheme. The N application rate was 80 kg N ha?1 yr?1 for the perennial crops and 240 kg N ha?1 yr?1 for the annual maize. A replicated field experiment was conducted with 1‐year measurements of soil fluxes of CH4, CO2 and N2O in weekly intervals using static chambers. The measurements revealed a clear seasonal trend in soil CO2 emissions, with highest emissions being found for the N‐fertilized Miscanthus plots (annual mean: 50 mg C m?² h?1). Significant differences between the cropping systems were found in soil N2O emissions due to their dependency on amount and timing of N fertilization. N‐fertilized maize plots had highest N2O emissions by far, which accumulated to 3.6 kg N2O ha?1 yr?1. The contribution of CH4 fluxes to the total soil greenhouse gas subsumption was very small compared with N2O and CO2. CH4 fluxes were mostly negative indicating that the investigated soils mainly acted as weak sinks for atmospheric CH4. To identify the system providing the best ratio of yield to soil N2O emissions, a subsumption relative to biomass yields was calculated. N‐fertilized maize caused the highest soil N2O emissions relative to dry matter yields. Moreover, unfertilized maize had higher relative soil N2O emissions than unfertilized Miscanthus and willow. These results favour perennial crops for bioenergy production, as they are able to provide high yields with low N2O emissions in the field. 相似文献