共查询到20条相似文献,搜索用时 31 毫秒
1.
Soil CO2 efflux is a major component of net ecosystem productivity (NEP) of forest systems. Combining data from multiple researchers for larger-scale modeling and assessment will only be valid if their methodologies provide directly comparable results. We conducted a series of laboratory and field tests to assess the presence and magnitude of soil CO2 efflux measurement system × environment interactions. Laboratory comparisons were made with a dynamic, steady-state CO2 flux generation apparatus, wherein gas diffusion drove flux without creating pressure differentials through three artificial soil media of varying air-filled porosity. Under these conditions, two closed systems (Li-6400-09 and SRC-1) exhibited errors that were dependent on physical properties of the artificial media. The open system (ACES) underestimated CO2 flux. However, unlike the two other systems, the ACES results could be corrected with a single calibration equation that was unaffected by physical differences in artificial media. Both scale and rank changes occurred among the measurement systems across four sites. Our work clearly shows that soil CO2 efflux measurement system × environment interactions do occur and can substantially impact estimates of soil CO2 efflux. Until reliable calibration techniques are developed and applied, such interactions make direct comparison of published rates, and C budgets estimated using such rates, difficult. 相似文献
2.
Hiroshi Koizumi Toshie Nakadai Youzou Usami Mitsumasa Satoh Masae Shiyomi Takehisa Oikawa 《Ecological Research》1991,6(3):227-232
In order to assess the validity of conventional methods for measuring CO2 flux from soil, the relationship between soil microbial respiration and ambient CO2 concentration was studied using an open-flow infra-red gas analyser (IRGA) method. Andosol from an upland field in central
Japan was used as a soil sample. Soil microbial respiration activity was depressed with the increase of CO2 concentration in ventilated air from 0 to 1000 ppmv. At 1000 ppmv, the respiration rate was less than half of that at 0 ppmv.
Thus, it is likely that soil respiration rate is overestimated by the alkali absorption method, because CO2 concentration in the absorption chamber is much lower than the normal level. Metabolic responses to CO2 concentration were different among groups of soil microorganisms. The bacteria actinomycetes group cultivated on agar medium
showed a more sensitive response to the CO2 concentration than the filamentous fungi group. 相似文献
3.
Efflux of carbon dioxide from snow-covered forest floors 总被引:1,自引:0,他引:1
The release of CO2 from the snow surface in winter and the soil surface in summer was directly or indirectly measured in four cool-temperate
deciduous broadleaved and evergreen needle forests. The closed chamber method (CC-method) and Fick's diffusion model (DM-method)
were used for the direct and indirect measurements, respectively. The winter soil temperatures from the soil surface to 10
cm depth were between 0 and 2°C. The concentration of CO2 within snowpack increased linearly with increasing snow depth. The average effluxes of CO2 calculated from the gradients of CO2 concentration in the snow using the DM-method ranged from 20 to 75 mg CO2 m−2 h−1, while the CC-method showed the average effluxes of 20 to 50 mg CO2m−2h−1. These results reveal that the snow thermally insulates the soil, allowing CO2 production to continue at soil temperatures a little above freezing throughout the winter. Carbon dioxide formed in the soil
can move across snowpack up to the atmosphere. The winter/summer ratio of CO2 emission was estimated to be higher than 7%. Therefore, the snow-covered soil served as a source of CO2 in the winter and the effluxes represent an important part of the annual CO2 budget in snowy regions. 相似文献
4.
Examination of the method for measuring soil respiration in cultivated land: Effect of carbon dioxide concentration on soil respiration 总被引:7,自引:1,他引:6
Toshie Nakadai Hiroshi Koizumi Youzou Usami Mitsumasa Satoh Takehisa Oikawa 《Ecological Research》1993,8(1):65-71
An acceleration of soil respiration with decreasing CO2 concentration was suggested in the field measurements. The result supporrs that obtained in laboratory experiments in our
previous study. The CO2 concentrations in a chamber of the alkali absorption method (the AA-method) were about 150–250 parts/106 lower than that in the atmosphere (about 350 parts/106), while those observed in the open-flow IRGA method (the OF-method) were nearly equal to the soil surface CO2 levels. The AA-method at such low CO2 levels in the chamber appears to overestimate the soil respiration. Our results showed that the rates obtained by the AA-method
were about twice as large as those by the OF-method in field and laboratory measurements. This finding has important consequences
with respect to the validity of the existing data obtained by the AA-method and the estimation of changes in the terrestrial
carbon flow with elevated CO2 相似文献
5.
The [CO2] in the xylem of tree stems is typically two to three orders of magnitude greater than atmospheric [CO2]. In this study, xylem [CO2] was experimentally manipulated in saplings of sycamore (Platanus occidentalis L.) and sweetgum (Liquidambar styraciflua L.) by allowing shoots severed from their root systems to absorb water containing [CO2] ranging from 0.04% to 14%. The effect of xylem [CO2] on CO2 efflux to the atmosphere from uninjured and mechanically injured, i.e., wounded, stems was examined. In both wounded and unwounded stems, and in both species, CO2 efflux was directly proportional to xylem [CO2], and increased 5-fold across the range of xylem [CO2] produced by the [CO2] treatment. Xylem [CO2] explained 76–77% of the variation in pre-wound efflux. After wounding, CO2 efflux increased substantially but remained directly proportional to internal stem [CO2]. These experiments substantiated our previous finding that stem CO2 efflux was directly related to internal xylem [CO2] and expanded our observations to two new species. We conclude that CO2 transported in the xylem may confound measurements of respiration based on CO2 efflux to the atmosphere. This study also provided evidence that the rapid increase in CO2 efflux observed after tissues are excised or injured is likely the result of the rapid diffusion of CO2 from the xylem, rather than an actual increase in the rate of respiration of wounded tissues. 相似文献
6.
On the assessment of root and soil respiration for soils of different textures: interactions with soil moisture contents and soil CO2 concentrations 总被引:10,自引:0,他引:10
Estimates of root and soil respiration are becoming increasingly important in agricultural and ecological research, but there
is little understanding how soil texture and water content may affect these estimates. We examined the effects of soil texture
on (i) estimated rates of root and soil respiration and (ii) soil CO2 concentrations, during cycles of soil wetting and drying in the citrus rootstock, Volkamer lemon (Citrus volkameriana Tan. and Pasq.). Plants were grown in soil columns filled with three different soil mixtures varying in their sand, silt
and clay content. Root and soil respiration rates, soil water content, plant water uptake and soil CO2 concentrations were measured and dynamic relationships among these variables were developed for each soil texture treatment.
We found that although the different soil textures differed in their plant-soil water relations characteristics, plant growth
was only slightly affected. Root and soil respiration rates were similar under most soil moisture conditions for soils varying
widely in percentages of sand, silt and clay. Only following irrigation did CO2 efflux from the soil surface vary among soils. That is, efflux of CO2 from the soil surface was much more restricted after watering (therefore rendering any respiration measurements inaccurate)
in finer textured soils than in sandy soils because of reduced porosity in the finer textured soils. Accordingly, CO2 reached and maintained the highest concentrations in finer textured soils (> 40 mmol CO2 mol−1). This study revealed that changes in soil moisture can affect interpretations of root and soil measurements based on CO2 efflux, particularly in fine textured soils. The implications of the present findings for field soil CO2 flux measurements are discussed.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
7.
Although CO2 efflux plays a critical role in carbon exchange between the biosphere and atmosphere, our understanding of its regulation by soil moisture is rather limited. This study was designed to examine the relationship between soil CO2 efflux and soil moisture in a natural ecosystem by taking advantage of the historically long drought period from 29 July to 21 September 2000 in the southern Central Great Plain, USA. At the end of August when soil moisture content at the top 50 mm was reduced to less than 50 g kg–1 gravimetrically, we applied 8 levels of water treatments (simulated to rainfall of 0, 10, 25, 50, 100, 150, 200, and 300 mm) with three replicates to 24 plots in a Tallgrass Prairie ecosystem in Central Oklahoma, USA. In order to quantify root-free soil CO2 efflux, we applied the same 8 levels of water treatments to 24 500-mm soil columns using soil from field adjacent to the experimental plots. We characterized dynamic patterns of soil moisture and soil CO2 efflux over the experimental period of 21 days. Both soil moisture content and CO2 efflux showed dramatic increases immediately after the water addition, followed by a gradual decline. The time courses in response to water treatments are well described by Y=Y0+ate–bt, where Y is either soil moisture or CO2 efflux, t is time, Y
0, a, and b are coefficients. Among the 8 water treatments, the maximal soil CO2 efflux rate occurred at the 50 mm water level in the field and 100 mm in the root-free soil 1 day after the treatment. The maximal soil CO2 efflux gradually shifted to higher water levels as the experiment continued. We found the relationship between soil CO2 efflux and soil moisture using the data from the 21-day experiment was highly scattered, suggesting complex mechanisms determining soil CO2 efflux by soil moisture. 相似文献
8.
Vincent J. Pacific Brian L. McGlynn Diego A. Riveros-Iregui Daniel L. Welsch Howard E. Epstein 《Biogeochemistry》2008,91(1):51-70
The spatial and temporal controls on soil CO2 production and surface CO2 efflux have been identified as outstanding gaps in our understanding of carbon cycling. We investigated both across two riparian-hillslope transitions in a subalpine catchment, northern Rocky Mountains, Montana. Riparian-hillslope transitions provide ideal locations for investigating the controls on soil CO2 dynamics due to strong, natural gradients in the factors driving respiration, including soil water content (SWC) and soil temperature. We measured soil air CO2 concentrations (20 and 50 cm), surface CO2 efflux, soil temperature, and SWC at eight locations. We investigated (1) how soil CO2 concentrations differed within and between landscape positions; (2) how the timing of peak soil CO2 concentrations varied across riparian and hillslope zones; and (3) whether higher soil CO2 concentrations necessarily resulted in higher efflux (i.e. did surface CO2 efflux follow patterns of subsurface CO2)? Soil CO2 concentrations were significantly higher in the riparian zones, likely due to higher SWC. The timing of peak soil CO2 concentrations also differed between riparian and hillslope zones, with highest hillslope concentrations near peak snowmelt and highest riparian concentrations during the late summer and early fall. Surface CO2 efflux was relatively homogeneous at monthly timescales as a result of different combinations of soil CO2 production and transport, which led to equifinality in efflux across the transects. However, efflux was 57% higher in the riparian zones when integrated to cumulative growing season efflux, and suggests higher riparian soil CO2 production. 相似文献
9.
Edoardo Daly Sari Palmroth Paul Stoy Mario Siqueira A. Christopher Oishi Jehn-Yih Juang Ram Oren Amilcare Porporato Gabriel G. Katul 《Biogeochemistry》2009,94(3):271-287
Profiles of subsurface soil CO2 concentration, soil temperature, and soil moisture, and throughfall were measured continuously during the years 2005 and
2006 in 16 locations at the free air CO2 enrichment facility situated within a temperate loblolly pine (Pinus taeda L.) stand. Sampling at these locations followed a 4 by 4 replicated experimental design comprised of two atmospheric CO2 concentration levels (ambient [CO2]a, ambient + 200 ppmv, [CO2]e) and two soil nitrogen (N) deposition levels (ambient, ambient + fertilization at 11.2 gN m−2 year−1). The combination of these measurements permitted indirect estimation of belowground CO2 production and flux profiles in the mineral soil. Adjacent to the soil CO2 profiles, direct (chamber-based) measurements of CO2 fluxes from the soil–litter complex were simultaneously conducted using the automated carbon efflux system. Based on the
measured soil CO2 profiles, neither [CO2]e nor N fertilization had a statistically significant effect on seasonal soil CO2, CO2 production, and effluxes from the mineral soil over the study period. Soil moisture and temperature had different effects
on CO2 concentration depending on the depth. Variations in CO2 were mostly explained by soil temperature at deeper soil layers, while water content was an important driver at the surface
(within the first 10 cm), where CO2 pulses were induced by rainfall events. The soil effluxes were equal to the CO2 production for most of the time, suggesting that the site reached near steady-state conditions. The fluxes estimated from
the CO2 profiles were highly correlated to the direct measurements when the soil was neither very dry nor very wet. This suggests
that a better parameterization of the soil CO2 diffusivity is required for these soil moisture extremes. 相似文献
10.
The aim of this study was to understand why two closed dynamic systems with a very similar design gave large differences in
soil CO2 efflux measurements (PP systems and LI-COR). Both in the field (forest beech stand) and in the laboratory, the PPsystems
gave higher estimations of soil CO2 efflux than the LI-COR system (ranging from 30% to 50%). The difference in wind speed occurring within the soil respiration
chambers (0.9 m s−1 within the SRC-1 and 0.4 m s−1 within the LI-6000-09 chambers) may account for the discrepancy between the two systems. An excessive air movement inside
the respiration chamber is thought to disrupt the high laminar boundary layer over the forest floor. This would promote an
exhaust of the CO2 accumulated into the upper soil layers into the chamber and a lateral diffusion of CO2 in the soil towards the respiration chamber. The discrepancy between the two systems was reduced (i) by decreasing fan speed
within the SRC-1, (ii) by increasing wind speed over the soil surface outside the respiration chamber, or (iii) by using an
artificial soil design without high CO2 concentration in soil pores. We show that wind speed is an important component of soil CO2 diffusion which must be taken into account when measuring soil CO2 efflux, even on very fine textured soil like silt-loam soil. Proper measurement can be achieved by maintaining wind speed
inside the chamber below 0.4 m s−1 since low wind speed conditions predominate under forest canopies. However, more accurate measurements will be obtained by
regulating wind speeds within the chamber at a velocity representative of the wind speed recorded simultaneously at the floor
surface.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
11.
The aim of this study was to evaluate a measuring technique for determining soil CO2 efflux from large soil samples having undisturbed structure under controlled laboratory conditions. Further objectives were
to use the developed measuring method for comparing soil CO2 efflux from samples, collected in three different soil management systems at various soil water content values. The experimental
technique was tested and optimised for timing of sampling by taking air samples after 1, 3 and 6 hours of incubation. Based
on the results, the incubation time was set to three hours. The CO2 efflux measured for different soil management systems was the highest in the no-till and the lowest in the ploughing treatment,
which was in accordance with measurements on accessible organic carbon for microbes. An increase in CO2 efflux with increasing soil water content was found in the studied soil water content range. Our results indicate that soil
respiration rates, measured directly after tillage operations, can highly differ from those measured long after. 相似文献
12.
Vose James M. Elliott Katherine J. Johnson Dale W. Tingey David T. Johnson Mark G. 《Plant and Soil》1997,190(1):19-28
We measured growing season soil CO2 evolution under elevated atmospheric [CO2] and soil nitrogen (N) additions. Our objectives were to determine treatment effects, quantify seasonal variation, and compare two measurement techniques. Elevated [CO2] treatments were applied in open-top chambers containing ponderosa pine (Pinus ponderosa L.) seedlings. N applications were made annually in early spring. The experimental design was a replicated factorial combination of CO2 (ambient, + 175, and +350 L L–1 CO2) and N (0, 10, and 20 g m–2 N as ammonium sulphate). Soils were irrigated to maintain soil moisture at > 25 percent. Soil CO2 evolution was measured over diurnal periods (20–22 hours) in October 1992, and April, June, and October 1993 and 1994 using a flow-through, infrared gas analyzer measurement system and corresponding pCO2 measurements were made with gas wells. Significantly higher soil CO2 evolution was observed in the elevated CO2 treatments; N effects were not significant. Averaged across all measurement periods, fluxes, were 4.8, 8.0, and 6.5 for ambient + 175 CO2, and +350 CO2 respectively).Treatment variation was linearly related to fungal occurrence as observed in minirhizotron tubes. Seasonal variation in soil CO2 evolution was non-linearly related to soil temperature; i.e., fluxes increased up to approximately soil temperature (10cm soil depth) and decreased dramatically at temperatures > 18°C. These patterns indicate exceeding optimal temperatures for biological activity. The dynamic, flow-through measurement system was weakly correlated (r = 0.57; p < 0.0001; n = 56) with the pCO2 measurement method. 相似文献
13.
Andrew D. Thomas 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2012,367(1606):3076-3086
Biological soil crusts (BSCs) are an important source of organic carbon, and affect a range of ecosystem functions in arid and semiarid environments. Yet the impact of grazing disturbance on crust properties and soil CO2 efflux remain poorly studied, particularly in African ecosystems. The effects of burial under wind-blown sand, disaggregation and removal of BSCs on seasonal variations in soil CO2 efflux, soil organic carbon, chlorophyll a and scytonemin were investigated at two sites in the Kalahari of southern Botswana. Field experiments were employed to isolate CO2 efflux originating from BSCs in order to estimate the C exchange within the crust. Organic carbon was not evenly distributed through the soil profile but concentrated in the BSC. Soil CO2 efflux was higher in Kalahari Sand than in calcrete soils, but rates varied significantly with seasonal changes in moisture and temperature. BSCs at both sites were a small net sink of C to the soil. Soil CO2 efflux was significantly higher in sand soils where the BSC was removed, and on calcrete where the BSC was buried under sand. The BSC removal and burial under sand also significantly reduced chlorophyll a, organic carbon and scytonemin. Disaggregation of the soil crust, however, led to increases in chlorophyll a and organic carbon. The data confirm the importance of BSCs for C cycling in drylands and indicate intensive grazing, which destroys BSCs through trampling and burial, will adversely affect C sequestration and storage. Managed grazing, where soil surfaces are only lightly disturbed, would help maintain a positive carbon balance in African drylands. 相似文献
14.
Spatial and temporal variation in soil CO2 efflux in an old-growth neotropical rain forest, La Selva, Costa Rica 总被引:2,自引:2,他引:0
Luitgard Schwendenmann Edzo Veldkamp Tania Brenes Joseph J. O'Brien Jens Mackensen 《Biogeochemistry》2003,64(1):111-128
Our objectives were to quantify and compare soil CO2 efflux of two dominant soil types in an old-growth neotropical rain forest in the Atlantic zone of Costa Rica, and to evaluate the control of environmental factors on CO2 release. We measured soil CO2 efflux from eight permanent soil chambers on six Oxisol sites. Three sites were developed on old river terraces (old alluvium) and the other three were developed on old lava flows (residual). At the same time we measured soil CO2 concentrations, soil water content and soil temperature at various depths in 6 soil shafts (3 m deep). Between old alluvium sites, the two-year average CO2 flux rates ranged from 117.3 to 128.9 mg C m–2 h–1. Significantly higher soil CO2 flux occurred on the residual sites (141.1 to 184.2 mg C m–2 h–1). Spatial differences in CO2 efflux were related to fine root biomass, soil carbon and phosphorus concentration but also to soil water content. Spatial variability in CO2 storage was high and the amount of CO2 stored in the upper and lower soil profile was different between old alluvial and residual sites. The major factor identified for explaining temporal variations in soil CO2 efflux was soil water content. During periods of high soil water content CO2 emission decreased, probably due to lower diffusion and CO2 production rates. During the 2-year study period inter-annual variation in soil CO2 efflux was not detected. 相似文献
15.
由于全球气候变化,预计未来我国亚热带地区干旱频率和持续时间将会增加。森林土壤CO2的释放是陆地生态系统碳循环的重要组成部分,然而,有关不同深度土壤CO2通量对干旱响应的理解仍相当有限。选择武夷山针叶林(Coniferous Forest,CF)和常绿阔叶林(Evergreen Broadleaved Forest,EBF)为研究对象,于2014年6月至2015年12月,采用梯度法计算10、30 cm和50 cm深度各层土壤CO2通量,探讨模拟干旱对其影响。结果表明:CF和EBF样地土壤CO2浓度均随土壤深度的增加而升高。CF和EBF样地对照(CK)处理10 cm深度土壤CO2生产量分别占总CO2生产量的53.5%和55.7%,表明土壤CO2生产量主要来源于浅层土壤,这可能与浅层土壤有高的有机碳含量及细根生物量主要分布区有关。干旱处理使CF和EBF样地不同深度土壤CO2通量均显著减少。在两个样地土壤CO2通量的温度敏感性(Q10)值均随着土壤深度的增加而减少。干旱处理显著减少了CF样地浅层土壤的Q10值(P=0.02),对深层土壤影响不显著(30 cm:P=0.30;50 cm:P=0.23);而在EBF样地干旱处理显著减少了深层土壤的Q10值(30 cm:P=0.02;50 cm:P=0.01),对浅层土壤影响不显著(P=0.32)。 相似文献
16.
Indirect partitioning of soil respiration in a series of evergreen forest ecosystems 总被引:1,自引:0,他引:1
A simple estimation of heterotrophic respiration can be obtained analytically as the y-intercept of the linear regression between soil-surface CO2 efflux and root biomass. In the present study, a development of this indirect methodology is presented by taking into consideration
both the temporal variation and the spatial heterogeneity of heterotrophic respiration. For this purpose, soil CO2 efflux, soil carbon content and main stand characteristics were estimated in seven evergreen forest ecosystems along an elevation
gradient ranging from 250 to 1740 m. For each site and for each sampling date the measured soil CO2 efflux (R
S) was predicted with the model R
S = a × S
C + b × R
D ± ε, where S
C is soil carbon content per unit area to a depth of 30 cm and R
D is the root density of the 2–5 mm root class. Regressions with statistically significant a and b coefficients allowed the indirect separation of the two components of soil CO2 efflux. Considering that the different sampling dates were characterized by different soil temperature, it was possible to
investigate the temporal and thermal dependency of autotrophic and heterotrophic respiration. It was estimated that annual
autotrophic respiration accounts for 16–58% of total soil CO2 efflux in the seven different evergreen ecosystems. In addition, our observations show a decrease of annual autotrophic respiration
at increasing availability of soil nitrogen.
Section Editor: A. Hodge 相似文献
17.
E. S. Bernhardt J. J. Barber J. S. Pippen L. Taneva J. A. Andrews W. H. Schlesinger 《Biogeochemistry》2006,77(1):91-116
Emissions of CO2 from soils make up one of the largest fluxes in the global C cycle, thus small changes in soil respiration may have large
impacts on global C cycling. Anthropogenic additions of CO2 to the atmosphere are expected to alter soil carbon cycling, an important component of the global carbon budget. As part
of the Duke Forest Free-Air CO2 Enrichment (FACE) experiment, we examined how forest growth at elevated (+200 ppmv) atmospheric CO2 concentration affects soil CO2 dynamics over 7 years of continuous enrichment. Soil respiration, soil CO2 concentrations, and the isotopic signature of soil CO2 were measured monthly throughout the 7 years of treatment. Estimated annual rates of soil CO2 efflux have been significantly higher in the elevated plots in every year of the study, but over the last 5 years the magnitude
of the CO2 enrichment effect on soil CO2 efflux has declined. Gas well samples indicate that over 7 years fumigation has led to sustained increases in soil CO2 concentrations and depletion in the δ13C of soil CO2 at all but the shallowest soil depths. 相似文献
18.
Soil respiration of Alaskan tundra at elevated atmospheric carbon dioxide concentrations 总被引:3,自引:0,他引:3
Summary CO2 efflux from tussock tundra in Alaska that had been exposed to elevated CO2 for 2.5 growing seasons was measured to assess the effect of long- and short-term CO2 enrichment on soil respiration. Long-term treatments were: 348, 514, and 683 μll−1 CO2 and 680 μll−1 CO2+4°C above ambient. Measurements were made at 5 CO2 concentrations between 87 and 680 μll−1 CO2. Neither long- or short-term CO2 enrichment significantly affected soil CO2 efflux. Tundra developed at elevated temperature and 680 μll−1 CO2 had slightly higher, but not statistically different, mean respiration rates compared to untreated tundra and to tundra under
CO2 control alone. 相似文献
19.
Separating the effects of moisture and temperature on soil CO2 efflux in a coniferous forest in the Sierra Nevada mountains 总被引:19,自引:0,他引:19
Separating the effects of soil temperature and moisture on soil CO2 efflux is critical to modeling and understanding the belowground carbon dynamics of forest ecosystems. We developed two analytical procedures to separate the effects of soil temperature and moisture, based on continuous measurements of the CO2 efflux, temperature and moisture of the soil at a ponderosa pine plantation in the Sierra Nevada Mountains in California, from May 1998 to August 1999. We found that the combined effects of temperature and moisture on the seasonal variation of soil CO2 efflux could be effectively separated and represented with the product of a temperature term and a moisture term. The relationship between soil CO2 efflux and temperature could be well described using a power function. This relationship was modified by soil moisture which affects only the coefficient, but not the exponent, of the power function. We also found that when soil moisture was held constant, the temperature effect explained 82% of the temporal variation in CO2 efflux of the soil. Similarly, when temperature was held constant, the moisture effects explained 84% of the variation. Temperature and moisture together explained 89% of the total temporal variations in soil CO2 efflux. A multiplicative formulation with power functions representing both temperature and moisture dependences was recommended for modeling soil CO2 efflux. This formulation can be used to model the seasonal trend of soil CO2 efflux of the forest based on temperature and moisture, two key variables influenced by climate change and management practices. 相似文献
20.
In forest ecosystems the single largest respiratory flux influencing net ecosystem productivity (NEP) is the total soil CO2 efflux; however, it is difficult to make measurements of this flux that are accurate at the ecosystem scale. We examined patterns of soil CO2 efflux using five different methods: auto-chambers, portable gas analyzers, eddy covariance along and two models parameterized with the observed data. The relation between soil temperature and soil moisture with soil CO2 effluxes are also investigated, both inter-annually and seasonally, using these observations/results. Soil respiration rates (R
soil) are greatest during the growing season when soil temperatures are between 15 and 25 °C, but some soil CO2 efflux occurs throughout the year. Measured soil respiration was sensitive to soil temperature, particularly during the spring and fall. All measurement methods produced similar annual estimates. Depending on the time of the year, the eddy covariance (flux tower) estimate for ecosystem respiration is similar to or slightly lower than estimates of annual soil CO2 efflux from the other methods. As the eddy covariance estimate includes foliar and stem respiration which the other methods do not; it was expected to be larger (perhaps 15–30%). The auto-chamber system continuously measuring soil CO2 efflux rates provides a level of temporal resolution that permits investigation of short- to longer term influences of factors on these efflux rates. The expense of building and maintaining an auto chamber system may not be necessary for those researchers interested in estimating R
soil annually, but auto-chambers do allow the capture of data from all seasons needed for model parameterization. 相似文献