Carbon exchange in a freshwater marsh in the Sanjiang Plain, northeastern China   总被引：1，自引：0，他引：1  

Changchun Song  Li Sun  Yao HuangYuesi Wang  Zhongmei Wan 《Agricultural and Forest Meteorology》2011,151(8):1131-1138

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 0-7.6 g C m⁻² d⁻¹, respectively. Ecosystem respiration (RE) displayed relatively smooth seasonal pattern with the range of 0.8-4.2 g C m⁻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 ± 9.2 g C m⁻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.  相似文献   

Seasonal variation and fire effects on CH₄, N₂O and CO₂ exchange in savanna soils of northern Australia     

Stephen J. Livesley  Samantha GroverLindsay B. Hutley  Hizbullah JamaliKlaus Butterbach-Bahl  Benedikt FestJason Beringer  Stefan K. Arndt 《Agricultural and Forest Meteorology》2011,151(11):1440-1452

Tropical savanna ecosystems are a major contributor to global CO₂, CH₄ and N₂O greenhouse gas exchange. Savanna fire events represent large, discrete C emissions but the importance of ongoing soil-atmosphere gas exchange is less well understood. Seasonal rainfall and fire events are likely to impact upon savanna soil microbial processes involved in N₂O and CH₄ exchange. We measured soil CO₂, CH₄ and N₂O fluxes in savanna woodland (Eucalyptus tetrodonta/Eucalyptus miniata trees above sorghum grass) at Howard Springs, Australia over a 16 month period from October 2007 to January 2009 using manual chambers and a field-based gas chromatograph connected to automated chambers. The effect of fire on soil gas exchange was investigated through two controlled burns and protected unburnt areas. Fire is a frequent natural and management action in these savanna (every 1-2 years). There was no seasonal change and no fire effect upon soil N₂O exchange. Soil N₂O fluxes were very low, generally between −1.0 and 1.0 μg N m⁻² h⁻¹, and often below the minimum detection limit. There was an increase in soil NH₄⁺ in the months after the 2008 fire event, but no change in soil NO₃⁻. There was considerable nitrification in the early wet season but minimal nitrification at all other times.Savanna soil was generally a net CH₄ sink that equated to between −2.0 and −1.6 kg CH₄ ha⁻¹ y⁻¹ with no clear seasonal pattern in response to changing soil moisture conditions. Irrigation in the dry season significantly reduced soil gas diffusion and as a consequence soil CH₄ uptake. There were short periods of soil CH₄ emission, up to 20 μg C m⁻² h⁻¹, likely to have been caused by termite activity in, or beneath, automated chambers. Soil CO₂ fluxes showed a strong bimodal seasonal pattern, increasing fivefold from the dry into the wet season. Soil moisture showed a weak relationship with soil CH₄ fluxes, but a much stronger relationship with soil CO₂ fluxes, explaining up to 70% of the variation in unburnt treatments. Australian savanna soils are a small N₂O source, and possibly even a sink. Annual soil CH₄ flux measurements suggest that the 1.9 million km² of Australian savanna soils may provide a C sink of between −7.7 and −9.4 Tg CO₂-e per year. This sink estimate would offset potentially 10% of Australian transport related CO₂-e emissions. This CH₄ sink estimate does not include concurrent CH₄ emissions from termite mounds or ephemeral wetlands in Australian savannas.  相似文献   

Methane uptake in soils from Pinus radiata plantations, a reverting shrubland and adjacent pastures: Effects of land-use change, and soil texture, water and mineral nitrogen     

K.R. Tate  D.J. Ross  C.B. Hedley  B.K. Singh 《Soil biology & biochemistry》2007,39(7):1437-1449

Afforestation and reforestation of pastures are key land-use changes in New Zealand that help sequester carbon (C) to offset its carbon dioxide (CO₂) emissions under the Kyoto Protocol. However, relatively little attention has been given so far to associated changes in trace gas fluxes. Here, we measure methane (CH₄) fluxes and CO₂ production, as well as microbial C, nitrogen (N) and mineral-N, in intact, gradually dried (ca. 2 months at 20 °C) cores of a volcanic soil and a heavier textured, non-volcanic soil collected within plantations of Pinus radiata D. Don (pine) and adjacent permanent pastures. CH₄ fluxes and CO₂ production were also measured in cores of another volcanic soil under reverting shrubland (mainly Kunzea var. ericoides (A. Rich) J. Thompson) and an adjacent pasture. CH₄ uptake in the pine and shrubland cores of the volcanic soils at field capacity averaged about 35 and 14 μg CH₄-C m⁻² h⁻¹, respectively, and was significantly higher than in the pasture cores (about 21 and 6 μg CH₄-C m⁻² h⁻¹, respectively). In the non-volcanic soil, however, CH₄-C uptake was similar in most cores of the pine and pasture soils, averaging about 7-9 μg m⁻² h⁻¹, except in very wet samples. In contrast, rates of CO₂ production and microbial C and N concentrations were significantly lower under pine than under pasture. In the air-dry cores, microbial C and N had declined in the volcanic soil, but not in the non-volcanic soil; ammonium-N, and especially nitrate-N, had increased significantly in all samples. CH₄ uptake was, with few exceptions, not significantly influenced by initial concentrations of ammonium-N or nitrate-N, nor by their changes on air-drying. A combination of phospholipid fatty acid (PLFA) and stable isotope probing (SIP) analyses of only the pine and pasture soils showed that different methanotrophic communities were probably active in soils under the different vegetations. The C18 PLFAs (type II methanotrophs) predominated under pine and C16 PLFAs (type I methanotrophs) predominated under pasture. Overall, vegetation, soil texture, and water-filled pore space influenced CH₄-C uptake more than did soil mineral-N concentrations.  相似文献   

Seasonal changes in the spatial structures of N₂O, CO₂, and CH₄ fluxes from Acacia mangium plantation soils in Indonesia     

Ryota Konda  Seiichi Ohta  Joko Heriyanto 《Soil biology & biochemistry》2010,42(9):1512-1522

We evaluated the spatial structures of nitrous oxide (N₂O), carbon dioxide (CO₂), and methane (CH₄) fluxes in an Acacia mangium plantation stand in Sumatra, Indonesia, in drier (August) and wetter (March) seasons. A 60 × 100-m plot was established in an A. mangium plantation that included different topographical elements of the upper plateau, lower plateau, upper slope and foot slope. The plot was divided into 10 × 10-m grids and gas fluxes and soil properties were measured at 77 grid points at 10-m intervals within the plot. Spatial structures of the gas fluxes and soil properties were identified using geostatistical analyses. Averaged N₂O and CO₂ fluxes in the wetter season (1.85 mg N m⁻² d⁻¹ and 4.29 g C m⁻² d⁻¹, respectively) were significantly higher than those in the drier season (0.55 mg N m⁻² d⁻¹ and 2.73 g C m⁻² d⁻¹, respectively) and averaged CH₄ uptake rates in the drier season (−0.62 mg C m⁻² d⁻¹) were higher than those in the wetter season (−0.24 mg C m⁻² d⁻¹). These values of N₂O fluxes in A. mangium soils were higher than those reported for natural forest soils in Sumatra, while CO₂ and CH₄ fluxes were in the range of fluxes reported for natural forest soils. Seasonal differences in these gas fluxes appears to be controlled by soil water content and substrate availability due to differing precipitation and mineralization of litter between seasons. N₂O fluxes had strong spatial dependence with a range of about 18 m in both the drier and wetter seasons. Topography was associated with the N₂O fluxes in the wetter season with higher and lower fluxes on the foot slope and on the upper plateau, respectively, via controlling the anaerobic-aerobic conditions in the soils. In the drier season, however, we could not find obvious topographic influences on the spatial patterns of N₂O fluxes and they may have depended on litter amount distribution. CO₂ fluxes had no spatial dependence in both seasons, but the topographic influence was significant in the drier season with lowest fluxes on the foot slope, while there was no significant difference between topographic positions in the wetter season. The distributions of litter amount and soil organic matter were possibly associated with CO₂ fluxes through their effects on microbial activities and fine root distribution in this A. mangium plantation.  相似文献   

Soil CO₂ flux in six monospecific forest plantations in Southern Rwanda     

D. Nsabimana  L. Klemedtson  G. Wallin 《Soil biology & biochemistry》2009,41(2):396-402

Forest soils contain the largest carbon stock of all terrestrial biomes and are probably the most important source of carbon dioxide (CO₂) to atmosphere. Soil CO₂ fluxes from 54 to 72-year-old monospecific stands in Rwanda were quantified from March 2006 to December 2007. The influences of soil temperature, soil water content, soil carbon (C) and nitrogen (N) stocks, soil pH, and stand characteristics on soil CO₂ flux were investigated. The mean annual soil CO₂ flux was highest under Eucalyptus saligna (3.92 μmol m⁻² s⁻¹) and lowest under Entandrophragma excelsum (3.13 μmol m⁻² s⁻¹). The seasonal variation in soil CO₂ flux from all stands followed the same trend and was highest in rainy seasons and lowest in dry seasons. Soil CO₂ flux was mainly correlated to soil water content (R² = 0.36-0.77), stand age (R² = 0.45), soil C stock (R² = 0.33), basal area (R² = 0.21), and soil temperature (R² = 0.06-0.17). The results contribute to the understanding of factors that influence soil CO₂ flux in monocultural plantations grown under the same microclimatic and soil conditions. The results can be used to construct models that predict soil CO₂ emissions in the tropics.  相似文献   

Increasing net CO₂ uptake by a Danish beech forest during the period from 1996 to 2009     

Kim Pilegaard  Andreas IbromMichael S. Courtney  Poul HummelshøjNiels Otto Jensen 《Agricultural and Forest Meteorology》2011,151(7):934-946

The exchange of CO₂ between the atmosphere and a beech forest near Sorø, Denmark, was measured continuously over 14 years (1996-2009). The simultaneous measurement of many parameters that influence CO₂ uptake makes it possible to relate the CO₂ exchange to recent changes in e.g. temperature and atmospheric CO₂ concentration. The net CO₂ exchange (NEE) was measured by the eddy covariance method. Ecosystem respiration (RE) was estimated from nighttime values and gross ecosystem exchange (GEE) was calculated as the sum of RE and NEE. Over the years the beech forest acted as a sink of on average of 157 g C m⁻² yr⁻¹. In one of the years only, the forest acted as a small source. During 1996-2009 a significant increase in annual NEE was observed. A significant increase in GEE and a smaller and not significant increase in RE was also found. Thus the increased NEE was mainly attributed to an increase in GEE. The overall trend in NEE was significant with an average increase in uptake of 23 g C m⁻² yr⁻². The carbon uptake period (i.e. the period with daily net CO₂ gain) increased by 1.9 days per year, whereas there was a non significant tendency of increase of the leafed period. This means that the leaves stayed active longer. The analysis of CO₂ uptake by the forest by use of light response curves, revealed that the maximum rate of photosynthetic assimilation increased by 15% during the 14-year period. We conclude that the increase in the overall CO₂ uptake of the forest is due to a combination of increased growing season length and increased uptake capacity. We also conclude that long time series of flux measurements are necessary to reveal trends in the data because of the substantial inter-annual variation in the flux.  相似文献   

Classification and assessment of turbulent fluxes above ecosystems in North-America with self-organizing feature map networks     

Andres Schmidt  Chad HansonJames Kathilankal  Beverly E. Law 《Agricultural and Forest Meteorology》2011,151(4):508-520

We determined key environmental and meteorological drivers that influence the magnitude of the fluxes of carbon dioxide, latent heat, and sensible heat using data from different vegetation types at 56 sites of the AmeriFlux network in combination with a self-organizing feature map neural network. The technique was combined with a subsequent k-means clustering procedure to classify the turbulent fluxes. This method is a direct approach to assess the importance of several environmental parameters for the turbulent exchange rates above vegetated areas, based on eddy covariance measurements. The synthesis of the available dataset was achieved by merging 225 pre-clusters of fluxes that were found by the SOFM into 9 final clusters exhibiting mean CO₂ fluxes from −5.8 μmol m⁻² s⁻¹ to 3.8 μmol m⁻² s⁻¹.The spatial and temporal comprehensive dataset covering 305 site years, combined with the independence from mechanistic ecological assumptions of the SOFM network approach provides an opportunity to assess the strength of the influence of various environmental parameters on the turbulent fluxes over vegetated areas. After ranking the environmental and meteorological variables according to their cluster separation strength, the pattern of turbulent fluxes turned out to be three times more sensitive to photosynthetic photon flux density and vegetation type than air temperature. Furthermore, the results indicate a strong influence of the water vapor deficit on the magnitude of the turbulent exchange.  相似文献   

Elevated CO₂ concentration and nitrogen fertilisation effects on N₂O and CH₄ fluxes and biomass production of Phleum pratense on farmed peat soil     

Riitta Kettunen  Sanna Saarnio  Jouko Silvola 《Soil biology & biochemistry》2005,37(4):739-750

The effects of elevated CO₂ supply on N₂O and CH₄ fluxes and biomass production of Phleum pratense were studied in a greenhouse experiment. Three sets of 12 farmed peat soil mesocosms (10 cm dia, 47 cm long) sown with P. pratense and equally distributed in four thermo-controlled greenhouses were fertilised with a commercial fertiliser in order to add 2, 6 or 10 g N m⁻². In two of the greenhouses, CO₂ concentration was kept at atmospheric concentration (360 μmol mol⁻¹) and in the other two at doubled concentration (720 μmol mol⁻¹). Soil temperature was kept at 15 °C and air temperature at 20 °C. Natural lighting was supported by artificial light and deionized water was used to regulate soil moisture. Forage was harvested and the plants fertilised three times during the basic experiment, followed by an extra fertilisations and harvests. At the end of the experiment CH₄ production and CH₄ oxidation potentials were determined; roots were collected and the biomass was determined. From the three first harvests the amount of total N in the aboveground biomass was determined. N₂O and CH₄ exchange was monitored using a closed chamber technique and a gas chromatograph. The highest N₂O fluxes (on average, 255 μg N₂O m⁻² h⁻¹ during period IV) occurred just after fertilisation at high water contents, and especially at the beginning of the growing season (on average, 490 μg N₂O m⁻² h⁻¹ during period I) when the competition of vegetation for N was low. CH₄ fluxes were negligible throughout the experiment, and for all treatments the production and oxidation potentials of CH₄ were inconsequential. Especially at the highest rates of fertilisation, the elevated supply of CO₂ increased above- and below-ground biomass production, but both at the highest and lowest rates of fertilisation, decreased the total amount of N in the aboveground dry biomass. N₂O fluxes tended to be higher under doubled CO₂ concentrations, indicating that increasing atmospheric CO₂ concentration may affect N and C dynamics in farmed peat soil.  相似文献   

Short-term effects of clearfelling on soil CO₂, CH₄, and N₂O fluxes in a Sitka spruce plantation     

Argyro Zerva 《Soil biology & biochemistry》2005,37(11):2025-2036

We examined the effects of forest clearfelling on the fluxes of soil CO₂, CH₄, and N₂O in a Sitka spruce (Picea sitchensis (Bong.) Carr.) plantation on an organic-rich peaty gley soil, in Northern England. Soil CO₂, CH₄, N₂O as well as environmental factors such as soil temperature, soil water content, and depth to the water table were recorded in two mature stands for one growing season, at the end of which one of the two stands was felled and one was left as control. Monitoring of the same parameters continued thereafter for a second growing season. For the first 10 months after clearfelling, there was a significant decrease in soil CO₂ efflux, with an average efflux rate of 4.0 g m⁻² d⁻¹ in the mature stand (40-year) and 2.7 g m⁻² d⁻¹ in clearfelled site (CF). Clearfelling turned the soil from a sink (−0.37 mg m⁻² d⁻¹) for CH₄ to a net source (2.01 mg m⁻² d⁻¹). For the same period, soil N₂O fluxes averaged 0.57 mg m⁻² d⁻¹ in the CF and 0.23 mg m⁻² d⁻¹ in the 40-year stand. Clearfelling affected environmental factors and lead to higher daily soil temperatures during the summer period, while it caused an increase in the soil water content and a rise in the water table depth. Despite clearfelling, CO₂ remained the dominant greenhouse gas in terms of its greenhouse warming potential.  相似文献   

Interannual and interseasonal soil CO₂ efflux and VOC exchange rates in a Mediterranean holm oak forest in response to experimental drought     

Dolores Asensio  Josep Peñuelas  Joan Llusià  Romà Ogaya  Iolanda Filella 《Soil biology & biochemistry》2007,39(10):2471-2484

Climate models predict drier conditions in the next decades in the Mediterranean basin. Given the importance of soil CO₂ efflux in the global carbon balance and the important role of soil monoterpene and volatile organic compounds (VOCs) in soil ecology, we aimed to study the effects of the predicted drought on soil CO₂, monoterpenes and other VOC exchange rates and their seasonal and interannual variations. We decreased soil water availability in a Mediterranean holm oak forest soil by means of an experimental drought system performed since 1999 to the present. Measurements of soil gas exchange were carried out with IRGA, GC and PTR-MS techniques during two annual campaigns of contrasting precipitation. Soil respiration was twice higher the wet year than the dry year (2.27±0.26 and 1.05±0.15, respectively), and varied seasonally from 3.76±0.85 μmol m⁻² s⁻¹ in spring, to 0.13±0.01 μmol m⁻² s⁻¹ in summer. These results highlight the strong interannual and interseasonal variation in CO₂ efflux in Mediterranean ecosystems. The drought treatment produced a significant soil respiration reduction in drought plots in the wet sampling period. This reduction was even higher in wet springs (43% average reduction). These results show (1) that soil moisture is the main factor driving seasonal and interannual variations in soil respiration and (2) that the response of soil respiration to increased temperature is constrained by soil moisture. The results also show an additional control of soil CO₂ efflux by physiology and phenology of trees and animals. Soil monoterpene exchange rates ranged from −0.01 to 0.004 nmol m⁻² s⁻¹, thus the contribution of this Mediterranean holm oak forest soil to the total monoterpenes atmospheric budget seems to be very low. Responses of individual monoterpenes and VOCs to the drought treatment were different depending on the compound. This suggests that the effect of soil moisture reduction in the monoterpenes and VOC exchange rates seems to be dependent on monoterpene and VOC type. In general, soil monoterpene and other VOC exchange rates were not correlated with soil CO₂ efflux. In all cases, only a low proportion of variance was explained by the soil moisture changes, since almost all VOCs increased their emission rates in summer 2005, probably due to the effect of high soil temperature. Results indicate thus that physical and biological processes in soil are controlling soil VOC exchange but further research is needed on how these factors interact to produce the observed VOCs exchange responses.  相似文献   

Rapid shift from denitrification to nitrification in soil after biogas residue application as indicated by nitrous oxide isotopomers     

Jan Reent Köster  Mehmet Senbayram  Roland Bol  Mark Butler  Klaus Dittert 《Soil biology & biochemistry》2011,43(8):1671-1677

Nitrous oxide (N₂O) is one of the major greenhouse gases emitted from soils, where it is mainly produced by nitrification and denitrification. It is well known that rates of N₂O release from soils are mainly determined by the availability of substrates and oxygen, but N₂O source apportioning, highly needed to advance N₂O mitigation strategies, still remains challenging. In this study, using an automated soil incubation system, the N₂O site preference, i.e. the intramolecular ¹⁵N distribution, was analyzed to evaluate the progression in N₂O source processes following organic soil amendment. Biogas fermentation residue (BGR; originating from food waste fermentation) was applied to repacked grassland soil cores and compared to ammonium sulfate (AS) application, both at rates equivalent to 160 kg NH₄⁺-N ha⁻¹, and to unamended soil (control). The soil cores were incubated in a helium-oxygen atmosphere with 20 kPa O₂ for 43 days at 80% water-filled pore space. 43-day cumulative N₂O emissions were highest with BGR treated soil accounting for about 1.68 kg N₂O-N ha⁻¹ while application of AS caused much lower fluxes of c. 0.23 kg N₂O-N ha⁻¹. Also, after BGR application, carbon dioxide (CO₂) fluxes showed a pronounced initial peak with steep decline until day 21 whereas with ammonium addition they remained at the background level. N₂O dual isotope and isotopomer analysis of gas samples collected from BGR treated soil indicated bacterial denitrification to be the main N₂O generating process during the first three weeks when high CO₂ fluxes signified high carbon availability. In contrast, in the second half after all added labile carbon substrates had been consumed, nitrification, i.e. the generation of N₂O via oxidation of hydroxylamine, gained in importance reaching roughly the same N₂O production rate compared to bacterial denitrification as indicated by N₂O SP. Overall in this study, bacterial denitrification seemed to be the main N₂O forming process after application of biogas residues and fluxes were mainly driven by available organic carbon.  相似文献   

Influence of water table levels on CO₂ emissions in a Colorado subalpine fen: an in situ microcosm study   总被引：1，自引：0，他引：1  

Rodney A. Chimner  David J. Cooper 《Soil biology & biochemistry》2003,35(3):345-351

We quantified the relationship between water table position and CO₂ emissions by manipulating water table levels for two summers in microcosms installed in a Colorado subalpine fen. Water levels were manipulated in the microcosms by either adding water or removing water and ranged from +10 cm above the soil surface to 40 cm below the soil surface, with ambient water levels in the fen averaging +3 and +2 cm above the soil surface during 1998 and 1999, respectively. Microcosm installation had no significant effect on CO₂ efflux; the 2 year means of natural and reference CO₂ efflux were 205.4 and 213.9 mg CO₂-C m⁻² h⁻¹, respectively (p=0.80). Mean CO₂ emissions were lowest at the highest water tables (water +6 to +10 cm above the soil surface), averaging 133.8 mg CO₂-C m⁻² h⁻¹, increased to 231.3 mg CO₂-C m⁻² h⁻¹ when the water table was +1 to +5 cm above the soil surface and doubled to 453.7 mg CO₂-C m⁻² h⁻¹, when the water table was 0-5 cm below the soil surface. However, further lowering of the water table had little additional effect on CO₂ emissions, which averaged 470.3 and 401.1 mg CO₂-C m⁻² h⁻¹ when the water table was 6-10 cm, and 11-40 cm beneath the soil surface, respectively. The large increase in CO₂ emissions as we experimentally lowered the water table beneath the soil surface, coupled with no increase in CO₂ emissions as we furthered lowered water tables beneath the soil surface, suggest the presence of an easily oxidized labile carbon pool near the soil surface.  相似文献   

Controls over pathways of carbon efflux from soils along climate and black spruce productivity gradients in interior Alaska     

E.S. Kane  D.W. Valentine 《Soil biology & biochemistry》2006,38(6):1438-1450

Small changes in C cycling in boreal forests can change the sign of their C balance, so it is important to gain an understanding of the factors controlling small exports like water-soluble organic carbon (WSOC) fluxes from the soils in these systems. To examine this, we estimated WSOC fluxes based on measured concentrations along four replicate gradients in upland black spruce (Picea mariana [Mill.] BSP) productivity and soil temperature in interior Alaska and compared them to concurrent rates of soil CO₂ efflux. Concentrations of WSOC in organic and mineral horizons ranged from 4.9 to 22.7 g C m⁻² and from 1.4 to 8.4 g C m⁻², respectively. Annual WSOC fluxes (4.5-12.0 g C m⁻² y⁻¹) increased with annual soil CO₂ effluxes (365-739 g C m⁻² y⁻¹) across all sites (R²=0.55, p=0.02), with higher fluxes occurring in warmer, more productive stands. Although annual WSOC flux was relatively small compared to total soil CO₂ efflux across all sites (<3%), its relative contribution was highest in warmer, more productive stands which harbored less soil organic carbon. The proportions of relatively bioavailable organic fractions (hydrophilic organic matter and low molecular weight acids) were highest in WSOC in colder, low-productivity stands whereas the more degraded products of microbial activity (fulvic acids) were highest in warmer, more productive stands. These data suggest that WSOC mineralization may be a mechanism for increased soil C loss if the climate warms and therefore should be accounted for in order to accurately determine the sensitivity of boreal soil organic C balance to climate change.  相似文献   

CO₂ emissions from subtropical arable soils of China     

Yunsheng Lou  Zhongpei Li  Taolin Zhang 《Soil biology & biochemistry》2004,36(11):1835-1842

CO₂ efflux plays a key role in carbon exchange between the biosphere and atmosphere, but our understanding of the mechanism controlling its temporal and spatial variations is limited. The purpose of this study is to determine annual soil CO₂ flux and assess its variations in arable subtropical soils of China in relation to soil temperature, moisture, rainfall, microbial biomass carbon (MBC) and dissolved organic carbon (DOC) using the closed chamber method. Soils were derived from three parent materials including granite (G), tertiary red sandstone (T) and quaternary red clay (Q). The experiment was conducted at the Ecological Station of Red Soil, The Chinese Academy of Sciences, in a subtropical region of China. The results showed that soil CO₂ flux had clear seasonal fluctuations with the maximum value in summer, the minimum in winter and intermediate in spring and autumn. Further, significant differences in soil CO₂ flux were found among the three red soils, generally in the order of G>T>Q. The average annual fluxes were estimated as 2.84, 2.13 and 1.41 kg CO₂ m⁻² year⁻¹ for red soils derived from G, T and Q, respectively. Soil temperature strongly affects the seasonal variability of soil CO₂ flux (85.0-88.5% of the variability), followed by DOC (55.8-84.4%) and rainfall (43.0-55.8%). The differences in soil CO₂ flux among the three red soils were partly explained by MBC (33.7-58.9% of the variability) and DOC (23.8-33.6%).  相似文献   

Elevation of atmospheric CO₂ and N-nutritional status modify nodulation, nodule-carbon supply, and root exudation of Phaseolus vulgaris L.     

Susan Haase  Angelika Kania  Volker Römheld 《Soil biology & biochemistry》2007,39(9):2208-2221

Increased root exudation and a related stimulation of rhizosphere-microbial growth have been hypothesised as possible explanations for a lower nitrogen- (N-) nutritional status of plants grown under elevated atmospheric CO₂ concentrations, due to enhanced plant-microbial N competition in the rhizosphere. Leguminous plants may be able to counterbalance the enhanced N requirement by increased symbiotic N₂ fixation. Only limited information is available about the factors determining the stimulation of symbiotic N₂ fixation in response to elevated CO₂.In this study, short-term effects of elevated CO₂ on quality and quantity of root exudation, and on carbon supply to the nodules were assessed in Phaseolus vulgaris, grown in soil culture with limited (30 mg N kg⁻¹ soil) and sufficient N supply (200 mg N kg⁻¹ soil), at ambient (400 μmol mol⁻¹) and elevated (800 μmol mol⁻¹) atmospheric CO₂ concentrations.Elevated CO₂ reduced N tissue concentrations in both N treatments, accelerated the expression of N deficiency symptoms in the N-limited variant, but did not affect plant biomass production. ¹⁴CO₂ pulse-chase labelling revealed no indication for a general increase in root exudation with subsequent stimulation of rhizosphere microbial growth, resulting in increased N-competition in the rhizosphere at elevated CO₂. However, a CO₂-induced stimulation in root exudation of sugars and malate as a chemo-attractant for rhizobia was detected in 0.5-1.5 cm apical root zones as potential infection sites. Particularly in nodules, elevated CO₂ increased the accumulation of malate as a major carbon source for the microsymbiont and of malonate with essential functions for nodule development. Nodule number, biomass and the proportion of leghaemoglobin-producing nodules were also enhanced. The release of nod-gene-inducing flavonoids (genistein, daidzein and coumestrol) was stimulated under elevated CO₂, independent of the N supply, and was already detectable at early stages of seedling development at 6 days after sowing.  相似文献   

The effects of drought and timing of precipitation on the inter-annual variation in ecosystem-atmosphere exchange in a Mediterranean grassland   总被引：2，自引：0，他引：2  

Marjan Jongen  João Santos PereiraLuis Miguel Igreja Aires  Casimiro Adrião Pio 《Agricultural and Forest Meteorology》2011,151(5):595-606

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Grazing intensity alters soil respiration in an alpine meadow on the Tibetan plateau   总被引：2，自引：0，他引：2  

Guangmin Cao  Wenhong Mo  Yingnian Li 《Soil biology & biochemistry》2004,36(2):237-243

Grazing intensity may alter the soil respiration rate in grassland ecosystems. The objectives of our study were to (1) determine the influence of grazing intensity on temporal variations in soil respiration of an alpine meadow on the northeastern Tibetan Plateau; and (2) characterise the temperature response of soil respiration under different grazing intensities. Diurnal and seasonal soil respiration rates were measured for two alpine meadow sites with different grazing intensities. The light grazing (LG) meadow site had a grazing intensity of 2.55 sheep ha⁻¹, while the grazing intensity of the heavy grazing (HG) meadow site, 5.35 sheep ha⁻¹, was approximately twice that of the LG site. Soil respiration measurements showed that CO₂ efflux was almost twice as great at the LG site as at the HG site during the growing season, but the diurnal and seasonal patterns of soil respiration rate were similar for the two sites. Both exhibited the highest annual soil respiration rate in mid-August and the lowest in January. Soil respiration rate was highly dependent on soil temperature. The Q₁₀ value for annual soil respiration was lower for the HG site (2.75) than for the LG site (3.22). Estimates of net ecosystem CO₂ exchange from monthly measurements of biomass and soil respiration revealed that during the period from May 1998 to April 1999, the LG site released 2040 g CO₂ m⁻² y⁻¹ to the atmosphere, which was about one third more than the 1530 g CO₂ m⁻² y⁻¹ released at the HG site. The results suggest that (1) grazing intensity alters not only soil respiration rate, but also the temperature dependence of soil CO₂ efflux; and (2) soil temperature is the major environmental factor controlling the temporal variation of soil respiration rate in the alpine meadow ecosystem.  相似文献   

Carbon dioxide, nitrous oxide and methane dynamics in boreal organic agricultural soils with different soil characteristics     

M. Maljanen  V.-M. Komulainen  P.J. Martikainen 《Soil biology & biochemistry》2004,36(11):1801-1808

The annual carbon dioxide (CO₂), nitrous oxide (N₂O) and methane (CH₄) dynamics were measured with static chambers on two organic agricultural soils with different soil characteristics. Site 1 had a peat layer of 30 cm, with an organic matter (OM) content of 74% in the top 20 cm. Site 2 had a peat layer of 70 cm but an OM content of only 40% in the top 20 cm. On both sites there were plots under barley and grass and also plots where the vegetation was removed. All soils were net sources of CO₂ and N₂O, but they consumed atmospheric CH₄. Soils under barley had higher net CO₂ emissions (830 g CO₂-C m⁻² yr⁻¹) and N₂O emissions (848 mg N₂O-N m⁻² yr⁻¹) than those under grass (395 g CO₂-C m⁻³ yr⁻¹ and 275 mg N₂O-N m⁻² yr⁻¹). Bare soils had the highest N₂O emissions, mean 2350 mg N₂O-N m⁻² yr⁻¹. The mean CH₄ uptake rate from vegetated soils was 100 mg CH₄-C m⁻³ yr⁻¹ and from bare soils 55 mg CH₄-C m⁻² yr⁻¹. The net CO₂ emissions were higher from Site 2, which had a high peat bulk density and a low OM content derived from the addition of mineral soil to the peat during the cultivation history of that site. Despite the differences in soil characteristics, the mean N₂O emissions were similar from vegetated peat soils from both sites. However, bare soils from Site 2 with mineral soil addition had N₂O emissions of 2-9 times greater than those from Site 1. Site 1 consumed atmospheric CH₄ at a higher rate than Site 2 with additional mineral soil. N₂O emissions during winter were an important component of the N₂O budget even though they varied greatly, ranging from 2 to 99% (mean 26%) of the annual emission.  相似文献   

Fluxes of CO₂, CH₄, and N₂O in an alpine meadow affected by yak excreta on the Qinghai-Tibetan plateau during summer grazing periods   总被引：1，自引：0，他引：1  

Xingwu Lin  Shiping Wang  Xiuzhi Ma  Caiyun Luo  Gaoming Jiang 《Soil biology & biochemistry》2009,41(4):718-725

To assess the impacts of yak excreta patches on greenhouse gas (GHG) fluxes in the alpine meadow of the Qinghai-Tibetan plateau, methane (CH₄), carbon dioxide (CO₂), and nitrous oxide (N₂O) fluxes were measured for the first time from experimental excreta patches placed on the meadow during the summer grazing seasons in 2005 and 2006. Dung patches were CH₄ sources (average 586 μg m⁻² h⁻¹ in 2005 and 199 μg m⁻² h⁻¹ in 2006) during the investigation period of two years, while urine patches (average −31 μg m⁻² h⁻¹ in 2005 and −33 μg m⁻² h⁻¹ in 2006) and control plots (average −28 μg m⁻² h⁻¹ in 2005 and −30 μg m⁻² h⁻¹ in 2006) consumed CH₄. The cumulative CO₂ emission for dung patches was about 36-50% higher than control plots during the experimental period in 2005 and 2006. The cumulative N₂O emissions for both urine and dung patches were 2.1-3.7 and 1.8-3.5 times greater than control plots in 2005 and 2006, respectively. Soil water-filled pore space (WFPS) explained 35% and 36% of CH₄ flux variation for urine patches and control plots, respectively. Soil temperature explained 40-75% of temporal variation of CO₂ emissions for all treatments. Temporal N₂O flux variation in urine patches (34%), dung patches (48%), and control (56%) plots was mainly driven by the simultaneous effect of soil temperature and WFPS. Although yak excreta patches significantly affected GHG fluxes, their contributions to the whole grazing alpine meadow in terms of CO₂ equivalents are limited under the moderate grazing intensity (1.45 yak ha⁻¹). However, the contributions of excreta patches to N₂O emissions are not negligible when estimating N₂O emissions in the grazing meadow. In this study, the N₂O emission factor of yak excreta patches varied with year (about 0.9-1.0%, and 0.1-0.2% in 2005 and 2006, respectively), which was lower than IPCC default value of 2%.  相似文献   

Fluxes of CO₂, CH₄ and N₂O from drained organic soils in deciduous forests     

K. von Arnold  M. Nilsson  P. Weslien 《Soil biology & biochemistry》2005,37(6):1059-1071

We examined net greenhouse gas exchange at the soil surface in deciduous forests on soils with high organic contents. Fluxes of CO₂, CH₄ and N₂O were measured using dark static chambers for two consecutive years in three different forest types; (i) a drained and medium productivity site dominated by birch, (ii) a drained and highly productive site dominated by alder and (iii) an undrained and highly productive site dominated by alder. Although the drained sites had shallow mean groundwater tables (15 and 18 cm, respectively) their average annual rates of forest floor CO₂ release were almost twice as high compared to the undrained site (1.9±0.4 and 1.7±0.3, compared to 1.0±0.2 kg CO₂ m⁻² yr⁻¹). The average annual CH₄ emission was almost 10 times larger at the undrained site (7.6±3.1 compared to 0.9±0.5 g CH₄ m⁻² yr⁻¹ for the two drained sites). The average annual N₂O emissions at the undrained site (0.1±0.05 g N₂O m⁻² yr⁻¹) were lower than at the drained sites, and the emissions were almost five times higher at the drained alder site than at the drained birch site (0.9±0.35 compared to 0.2±0.11 g N₂O m⁻² yr⁻¹). The temporal variation in forest floor CO₂ release could be explained to a large extent by differences in groundwater table and air temperature, but little of the variation in the CH₄ and N₂O fluxes could be explained by these variables. The measured soil variables were only significant to explain for the within-site spatial variation in CH₄ and N₂O fluxes at the undrained swamp, and dark forest floor CO₂ release was not explained by these variables at any site. The between-site spatial variation was attributed to variations in drainage, groundwater level position, productivity and tree species for all three gases. The results indicate that N₂O emissions are of greater importance for the net greenhouse gas exchange at deciduous drained forest sites than at coniferous drained forest sites.  相似文献