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1.
Eleneide Doff sotta Patrick Meir† Yadvinder Malhi† Antonio Donato nobre‡ Martin Hodnett§ John Grace† 《Global Change Biology》2004,10(5):601-617
This study investigated the spatial and temporal variation in soil carbon dioxide (CO2) efflux and its relationship with soil temperature, soil moisture and rainfall in a forest near Manaus, Amazonas, Brazil. The mean rate of efflux was 6.45±0.25 SE μmol CO2 m?2s?1 at 25.6±0.22 SE°C (5 cm depth) ranging from 4.35 to 9.76 μmol CO2 m?2s?1; diel changes in efflux were correlated with soil temperature (r2=0.60). However, the efflux response to the diel cycle in temperature was not always a clear exponential function. During period of low soil water content, temperature in deeper layers had a better relationship with CO2 efflux than with the temperature nearer the soil surface. Soil water content may limit CO2 production during the drying‐down period that appeared to be an important factor controlling the efflux rate (r2=0.39). On the other hand, during the rewetting period microbial activity may be the main controlling factor, which may quickly induce very high rates of efflux. The CO2 flux chamber was adapted to mimic the effects of rainfall on soil CO2 efflux and the results showed that efflux rates reduced 30% immediately after a rainfall event. Measurements of the CO2 concentration gradient in the soil profile showed a buildup in the concentration of CO2 after rain on the top soil. This higher CO2 concentration developed shortly after rainfall when the soil pores in the upper layers were filled with water, which created a barrier for gas exchange between the soil and the atmosphere. 相似文献
2.
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
3.
B. W. SULLIVAN S. DORE T. E. KOLB S. C. HART M. C. MONTES‐HELU 《Global Change Biology》2010,16(9):2449-2460
Better understanding of variation in soil carbon dioxide (CO2) efflux caused by measurement techniques is needed, especially over gradients of site disturbance, to accurately estimate the global carbon cycle. We present soil CO2 efflux data from a gradient of disturbance to ponderosa pine (Pinus ponderosa C. Lawson var. scopulorum Engelm.) forests in northern Arizona, USA that were obtained using four different techniques: vented static chambers, a Licor 6400‐09, and soil CO2 diffusion profiles using two different models (Moldrup, Millington–Quirk) to estimate soil gas diffusivity. We also compared soil CO2 efflux measured by the Moldrup and Millington–Quirk diffusion profile methods to nighttime total ecosystem respiration (TER) data from an eddy covariance tower. We addressed four questions: (1) Does the use of a given method to measure soil CO2 efflux bias results across a disturbance gradient? (2) Does the magnitude of difference between observed and modeled estimates of soil CO2 differ between methods and across sites? (3) What is the spatial variability of each method at each site? (4) Which method is closest to the estimate of TER measured by the eddy covariance tower? Although soil CO2 efflux varied significantly among methods the differences were consistent among sites. Measured and modeled total growing season fluxes were generally higher for the Licor 6400‐09 and Millington–Quirk diffusion gradient methods compared with static chamber and the Moldrup diffusion gradient methods. A power analysis showed that the larger static chamber was the most efficient method at sampling spatial variation in soil CO2 efflux. Nighttime measurements of soil CO2 efflux from the Moldrup diffusion gradient method were most strongly related to nighttime TER assessed with eddy covariance. The use of a single, well‐implemented method to measure soil CO2 efflux is unlikely to create bias in comparisons across a gradient of forest disturbance. 相似文献
4.
ERIC A. DAVIDSON KATHLEEN E. SAVAGE SUSAN E. TRUMBORE† WERNER BORKEN ‡ 《Global Change Biology》2006,12(6):944-956
The major driving factors of soil CO2 production – substrate supply, temperature, and water content – vary vertically within the soil profile, with the greatest temporal variations of these factors usually near the soil surface. Several studies have demonstrated that wetting and drying of the organic horizon contributes to temporal variation in summertime soil CO2 efflux in forests, but this contribution is difficult to quantify. The objectives of this study were to partition CO2 production vertically in a mixed hardwood stand of the Harvard Forest, Massachusetts, USA, and then to use that partitioning to evaluate how the relative contributions of CO2 production by genetic soil horizon vary seasonally and interannually. We measured surface CO2 efflux and vertical soil profiles of CO2 concentration, temperature, water content, and soil physical characteristics. These data were applied to a model of effective diffusivity to estimate CO2 flux at the top of each genetic soil horizon and the production within each horizon. A sensitivity analysis revealed sources of uncertainty when applying a diffusivity model to a rocky soil with large spatial heterogeneity, especially estimates of bulk density and volumetric water content and matching measurements of profiles and surface fluxes. We conservatively estimate that the O horizon contributed 40–48% of the total annual soil CO2 efflux. Although the temperature sensitivity of CO2 production varied across soil horizons, the partitioning of CO2 production by horizon did not improve the overall prediction of surface CO2 effluxes based on temperature functions. However, vertical partitioning revealed that water content covaried with CO2 production only in the O horizon. Large interannual variations in estimates of O horizon CO2 production indicate that this layer could be an important transient interannual source or sink of ecosystem C. 相似文献
5.
Mark S. Johnson Eduardo Guimar?es Couto Osvaldo B. Pinto Jr Juliana Milesi Ricardo S. Santos Amorim Indira A. M. Messias Marcelo Sacardi Biudes 《PloS one》2013,8(6)
The Pantanal is a biodiversity hotspot comprised of a mosaic of landforms that differ in vegetative assemblages and flooding dynamics. Tree islands provide refuge for terrestrial fauna during the flooding period and are particularly important to the regional ecosystem structure. Little soil CO2 research has been conducted in this region. We evaluated soil CO2 dynamics in relation to primary controlling environmental parameters (soil temperature and soil water). Soil respiration was computed using the gradient method using in situ infrared gas analyzers to directly measure CO2 concentration within the soil profile. Due to the cost of the sensors and associated equipment, this study was unreplicated. Rather, we focus on the temporal relationships between soil CO2 efflux and related environmental parameters. Soil CO2 efflux during the study averaged 3.53 µmol CO2 m−2 s−1, and was equivalent to an annual soil respiration of 1220 g C m−2 y−1. This efflux value, integrated over a year, is comparable to soil C stocks for 0–20 cm. Soil water potential was the measured parameter most strongly associated with soil CO2 concentrations, with high CO2 values observed only once soil water potential at the 10 cm depth approached zero. This relationship was exhibited across a spectrum of timescales and was found to be significant at a daily timescale across all seasons using conditional nonparametric spectral Granger causality analysis. Hydrology plays a significant role in controlling CO2 efflux from the tree island soil, with soil CO2 dynamics differing by wetting mechanism. During the wet-up period, direct precipitation infiltrates soil from above and results in pulses of CO2 efflux from soil. The annual flood arrives later, and saturates soil from below. While CO2 concentrations in soil grew very high under both wetting mechanisms, the change in soil CO2 efflux was only significant when soils were wet from above. 相似文献
6.
皆伐火烧对亚热带森林不同深度土壤CO2通量的影响 总被引:1,自引:0,他引:1
评估不同深度土壤的CO_2通量是研究土壤碳动态的重要手段。目前有关皆伐火烧对森林土壤碳排放的影响研究仅局限于表层土壤,而对不同深度土壤碳排放影响鲜见报道。以米槠(Castanopsis carlesii)次生林(对照)及其皆伐火烧后林地为研究对象,利用非红外散射CO_2探头测定土壤CO_2浓度,并结合Fick第一扩散法则估算不同深度(0—80 cm)土壤CO_2通量。结果表明:(1)皆伐火烧改变土壤向大气排放的表观CO_2通量,在皆伐火烧后的2个月内土壤表观CO_2通量显著高于对照68%;2个月后,土壤表观CO_2通量低于对照37%。(2)皆伐火烧后,除10—20 cm的CO_2通量提高外,其余各深度(0—10、20—40、40—60 cm和60—80 cm)的CO_2通量均降低。同时,皆伐火烧改变不同土层对土壤呼吸的贡献率,降低0—10 cm土层的贡献率,提高10—20 cm土层的贡献率。(3)对照样地仅0—10 cm土壤CO_2通量与温度呈显著指数相关,10—40 cm深度CO_2通量则与土壤含水率呈显著线性相关。皆伐火烧后0—10 cm和10—20 cm处土壤的CO_2通量均与温度呈指数相关。说明皆伐火烧改变了不同深度土壤CO_2通量对于环境因子的响应。因此为准确评估和预测皆伐火烧对土壤与大气间碳交换的影响,应考虑皆伐火烧后不同时期土壤CO_2通量的变化,以及不同深度土壤CO_2通量对皆伐火烧的响应。 相似文献
7.
Soil respiration in Pinus tabulaeformis forest during dormant period at Huoditang forest zone in the Qinling Mountains, China
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Soil CO2 efflux in forest ecosystems during dormant season is one of the key components of the forest ecosystem carbon balance. Little work has been done to quantify soil CO2 efflux in most forests in China in special time because of difficulty in taking measurements. Soil respiration in a natural secondary Pinus tabulaeformis forest at Huoditang in the Qinling Mountains was measured from October to December in 2006 by means of open-path dynamic chamber technique. Relationships of soil respiration rate (Rs) with mean soil temperature (MST) and mean volumetric soil moisture content (MVSC) in different depths (0-5 cm and 5-10 cm) were examined in the current study. We found that (1) At the same observation site (upper-part, middle-part or under-part), there were tremendous temporal and spatial variations in Rs with variation coefficients of 48.38%, 82.51% and 81.88% in October, November and December, respectively; (2) There was a significant exponent relationship between diurnal mean soil respiration rate (Fc) and diurnal mean soil temperature (DMST) when DMST > 8.5°C for both soil depths (0-5 cm and 5-10 cm) examined. The temperature sensitivity of soil respiration, known as the Q10 value, was 1.297 and 1.323 in soil depths of 0-5 cm and 5-10 cm, respectively; (3) Relationship between Rs and MVSC was complex in soil depths of 0-5 cm and 5-10 cm; (4) Soil CO2 efflux from October to December in 2006 in the experimental area was (977.37 ± 88.43) to (997.19 ± 80.73) gCm−2 (p = 0.005). 相似文献
8.
Marian Pavelka Manuel Acosta Michal V. Marek Werner Kutsch Dalibor Janous 《Plant and Soil》2007,292(1-2):171-179
The parameter Q10 is commonly used to express the relationship between soil CO2 efflux and soil temperature. One advantage of this parameter is its application in a model expression of respiration losses
of different ecosystems. Correct specification of Q10 in these models is indispensable. Soil surface CO2 efflux and soil temperature at different depths were measured in a 21-year-old Norway spruce stand and a mountain grassland
site located at the Experimental Ecological Study Site Bily Kriz, Beskydy Mts. (NE Czech Republic), using automated gasometric
systems. A time-delay and goodness-of-fit between soil CO2 efflux and soil temperature at different measuring depths were determined. Wide ranges of values for the time-delay of CO2 efflux in response to temperature, Q10 and the determination coefficient (R2) between CO2 efflux and temperature were obtained at the both sites. The values of Q10 and the CO2 time-delay increased with depth, while the R2 of the CO2-temperature relationship significantly decreased. Soil temperature records obtained close to the soil surface showed the
highest values of R2 and the lowest value of the time-delay at both sites. Measurement of soil temperature at very shallow soil layer, preferably
at the soil surface, is highly recommended to determine useable values of Q10. We present a new procedure to normalize Q10 values for soil temperatures measured at different depths that would facilitate comparison of different sites. 相似文献
9.
A comparison of field methods for measuring soil carbon dioxide evolution: Experiments and simulation 总被引:7,自引:0,他引:7
Three widely used methods for measuring total soil CO2 evolution are evaluated, including the dynamic CO2 absorption method, the static CO2 absorption method and the closed chamber method. The study covers laboratory experiments. numerical experiments with a simulation model and field measurements. The results are used to perform an error analysis. The aim of this error analysis is to indicate the impact of each method on the CO2 dynamics during the measurement, and to select the most suitable method for frequent field usage.Laboratory experiments and simulation results show that the dynamic CO2 absorption method has the potential to absorb all CO2 evolving at the soil surface. The results also prove that the method has only a minor impact on the CO2 concentration-depth gradient and the CO2 efflux. The static CO2 absorption method underestimates the soil CO2 evolution, because the absorption velocity is too low, due to slow diffusion processes. Measurements with the closed-chamber method are based on an increasing concentration with time under a closed cover. However, the accumulation of gas alters the concentration gradient in the soil profile and thus causes a rapidly decreasing efflux during the measurement. A commonly used mathematical procedure, which corrects for the altered concentration gradient, does not yield the exact surface efflux, because the effect of increasing storage in the soil profile is not incorporated. Field measurements of CO2 evolution, using the closed-chamber method and the dynamic CO2 absorption method confirm the trends that have been predicted by the simulation model. The results of this study indicate that the dynamic CO2 absorption method is accurate. As it is cheap and simple, it is suitable for the study of temporal and spatial dynamics of CO2 evolution from the soil. 相似文献
10.
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
11.
秦岭火地塘林区油松(Pinus tabulaeformis)林休眠期的土壤呼吸 总被引:3,自引:2,他引:1
林木休眠期林地土壤CO2释放是森林生态系统碳平衡关键组成部分之一.由于绝大多数森林生态系统林木休眠期土壤CO2释放过程测定困难,国内有关林木休眠期CO2释放,量化方面的研究开展较少.采用动态开路气室法对秦岭火地塘林区天然次生油松(Pinus tabulaeformis)林土壤呼吸的日变化进行了测定,分析了土壤呼吸速率(mgCO2m-2h-1)与土壤温度和体积含水率的关系,基于土壤日均呼吸速率和土壤日均温度指数方程与观测季的总天数,估算了林木休眠期林地土壤CO2释放量.结果表明:(1)研究区林地土壤呼吸速率存在较大的时、空变异.不同观测部位土壤呼吸速率的峰值出现时间各异,呼吸作用较弱的时段也不一致.同一观测部位不同观测月中,土壤日均呼吸速率变异系数分别为48.38%,82.51%和81.88%;(2)当土温>8.5 ℃时,0~5 cm和5~10 cm土层,土壤日均温与土壤日均呼吸速率间存在极显著(p<0.001)的指数关系,Q10分别为1.297和1.323;(3)0~5 cm和5~10 cm土层,土壤体积含水率与土壤呼吸速率间关系复杂;(4) 林木休眠期研究区林地土壤CO2释放量变化于(977.37±88.43)~(997.19±80.73) gCm-2(p=0.005)间. 相似文献
12.
Soils play a key role in the global cycling of carbon (C), storing organic C, and releasing CO2 to the atmosphere. Although a large number of studies have focused on the CO2 flux at the soil–air interface, relatively few studies have examined the rates of CO2 production in individual layers of a soil profile. Deeper soil horizons often have high concentrations of CO2 in the soil air, but the sources of this CO2 and the spatiotemporal dynamics of CO2 production throughout the soil profile are poorly understood. We studied CO2 dynamics in six soil profiles arrayed across a grassland hillslope in coastal southern California. Gas probes were installed in each profile and gas samples were collected weekly or biweekly over a three-year period. Using soil air CO2 concentration data and a model based on Fick’s law of diffusion, we modeled the rates of CO2 production with soil profile depth. The CO2 diffusion constants were checked for accuracy using measured soil air 222Rn activities. The modeled net CO2 production rates were compared with CO2 fluxes measured at the soil surface. In general, the modeled and measured net CO2 fluxes were very similar although the model consistently underestimated CO2 production rates in the surficial soil horizons when the soils were moist. Profile CO2 production rates were strongly affected by the inter- and intra-annual variability in rainfall; rates were generally 2–10 times higher in the wet season (December to May) than in the dry season (June to November). The El Niño event of 1997–1998, which brought above-average levels of rainfall to the study site, significantly increased CO2 production in both the surface and subsurface soil horizons. Whole profile CO2 production rates were approximately three times higher during the El Niño year than in the following years of near-average rainfall. During the dry season, when the net rates of CO2 flux from the soil profiles are relatively low (4–11 mg C– CO2 m−2 h−1), 20%–50% of the CO2 diffusing out of the profiles appears to originate in the relatively moist soil subsurface (defined here as those horizons below 40 cm in depth). The natural abundance 14C signatures of the CO2 and soil organic C suggest that the subsurface CO2 is derived from the microbial mineralization of recent organic C, possibly dissolved organic C transported to the subsurface horizons during the wet season. 相似文献
13.
Soil CO2 efflux and pCO2 in the soil atmosphere were measured during one year at three montane sites of Mediterranean sclerophyllous forests in NE Spain. Two sites were located in the upper and lower slopes of a small catchment in the Prades mountains (mean precipitation 550 mm year–1), and a third site was located on a lower slope in the Montseny mountains (mean precipitation 900 mm year–1). The three sites were similar in bedrock and vegetation, but differed in soil characteristics and water availability. Seasonal variation of CO2 efflux and soil pCO2 were affected by soil temperature and, to a lesser extent, by soil moisture. Annual mean soil CO2 efflux (considered as soil respiration) was similar at Montseny and at the comparably located site at Prades (83 ± 18 S.E. vs. 75 ± 9 mg CO2 m–2 hour–1 , respectively), and was highest at the Prades upper slope site (122 ± 22 mg C02 m–2 hour–1 ). Despite those relatively similar CO2 effluxes, mean soil pCO2 was much higher at both Prades sites than at Montseny. Soil pCO2 always increased with depth at Prades while maxima pCO2 at Montseny were often at 20–30 cm depth. A model based on gas diffusion theory was able to explain why soil pCO2 was much higher at Prades than at Montseny, and to reproduce the shape of the vertical profile of pCO2 at the Prades soils. Nevertheless, the model failed to simulate the soil pCO2 maximum found at 20–30 cm depth at the Montseny site. Model simulations using a time-variable CO2 production rate suggested that pCO2 maxima at intermediate depth could be the result of a transient situation instead of an equilibrium one. 相似文献
14.
Ana Rey 《Global Change Biology》2015,21(5):1752-1761
Widespread recognition of the importance of soil CO2 efflux as a major source of CO2 to the atmosphere has led to active research. A large soil respiration database and recent reviews have compiled data, methods, and current challenges. This study highlights some deficiencies for a proper understanding of soil CO2 efflux focusing on processes of soil CO2 production and transport that have not received enough attention in the current soil respiration literature. It has mostly been assumed that soil CO2 efflux is the result of biological processes (i.e. soil respiration), but recent studies demonstrate that pedochemical and geological processes, such as geothermal and volcanic CO2 degassing, are potentially important in some areas. Besides the microbial decomposition of litter, solar radiation is responsible for photodegradation or photochemical degradation of litter. Diffusion is considered to be the main mechanism of CO2 transport in the soil, but changes in atmospheric pressure and thermal convection may also be important mechanisms driving soil CO2 efflux greater than diffusion under certain conditions. Lateral fluxes of carbon as dissolved organic and inorganic carbon occur and may cause an underestimation of soil CO2 efflux. Traditionally soil CO2 efflux has been measured with accumulation chambers assuming that the main transport mechanism is diffusion. New techniques are available such as improved automated chambers, CO2 concentration profiles and isotopic techniques that may help to elucidate the sources of carbon from soils. We need to develop specific and standardized methods for different CO2 sources to quantify this flux on a global scale. Biogeochemical models should include biological and non‐biological CO2 production processes before we can predict the response of soil CO2 efflux to climate change. Improving our understanding of the processes involved in soil CO2 efflux should be a research priority given the importance of this flux in the global carbon budget. 相似文献
15.
Mizue Ohashi Tomo’omi Kumagai Tomonori Kume Koichiro Gyokusen Taku M. Saitoh Masakazu Suzuki 《Biogeochemistry》2008,90(3):275-289
Although soil carbon dioxide (CO2) efflux from tropical forests may play an important role in global carbon (C) balance, our knowledge of the fluctuations
and factors controlling soil CO2 efflux in the Asian tropics is still poor. This study characterizes the temporal and spatial variability in soil CO2 efflux in relation to temperature/moisture content and estimates annual efflux from the forest floor in an aseasonal intact
tropical rainforest in Sarawak, Malaysia. Soil CO2 efflux varied widely in space; the range of variation averaged 17.4 μmol m−2 s−1 in total. While most CO2 flux rates were under 10 μmol m−2 s−1, exceptionally high fluxes were observed sporadically at several sampling points. Semivariogram analysis revealed little
spatial dependence in soil CO2 efflux. Temperature explained nearly half of the spatial heterogeneity, but the effect varied with time. Seasonal variation
in CO2 efflux had no fixed pattern, but was significantly correlated with soil moisture content. The correlation coefficient with
soil moisture content (SMC) at 30 and 60 cm depth was higher than at 10 cm depths. The annual soil CO2 efflux, estimated from the relationship between CO2 efflux and SMC at 30 cm depth, was 165 mol m−2 year−1 (1,986 g C m−2 year−1). As this area is known to suffer severe drought every 4–5 years caused by the El Nino-Southern Oscillation, the results
suggest that an unpredictable dry period might affect soil CO2 efflux, leading an annual variation in soil C balance. 相似文献
16.
Effects of soil phosphorus availability,temperature and moisture on soil respiration in Eucalyptus pauciflora forest 总被引:33,自引:1,他引:33
Rates of soil respiration (CO2 efflux) were measured for a year in a mature Eucalyptus pauciflora forest in unfertilized and phosphorus-fertilized plots. Soil CO2 efflux showed a distinct seasonal trend, and average daily rates ranged from 124 to 574 mg CO2 m–2 hr–1. Temperature and moisture are the main variables that cause variation in soil CO2 efflux; hence their effects were investigated over a year so as to then differentiate the treatment effect of phosphorus (P) nutrition.Soil temperature had the greatest effect on CO2 efflux and exhibited a highly significant logarithmic relationship (r2 = 0.81). Periods of low soil and litter moisture occurred during summer when temperatures were greater than 10 °C, and this resulted in depression of soil CO2 efflux. During winter, when temperatures were less than 10 °C, soil and litter moisture were consistently high and thus their variation had little effect on soil CO2 efflux. A multiple regression model including soil temperature, and soil and litter moisture accounted for 97% of the variance in rates of CO2 efflux, and thus can be used to predict soil CO2 efflux at this site with high accuracy. Total annual efflux of carbon from soil was estimated to be 7.11 t C ha–1 yr–1. The model was used to predict changes in this annual flux if temperature and moisture conditions were altered. The extent to which coefficients of the model differ among sites and forest types requires testing.Increased soil P availability resulted in a large increase in stem growth of trees but a reduction in the rate of soil CO2 efflux by approximately 8%. This reduction is suggested to be due to lower root activity resulting from reduced allocation of assimilate belowground. Root activity changed when P was added to microsites within plots, and via the whole tree root system at the plot level. These relationships of belowground carbon fluxes with temperature, moisture and nutrient availability provide essential information for understanding and predicting potential changes in forest ecosystems in response to land use management or climate change. 相似文献
17.
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
18.
In the context of an ongoing monitoring study of the Cabo de Gata-Níjar Natural Park (SE of Spain), we explored the use of soil respiration as an indicator of ecosystem functioning reflecting changes in ecological processes in semiarid environments. With this purpose, we measured soil CO2 efflux in six different and representative ecosystems of the Natural Park, with different land uses (forest and agricultural sites) and under different soil covers (under plant and bare soil) in two distinctive periods of the year: summer (dry period) and spring (growing season). We also measured the main soil properties and environmental variables. Soil CO2 efflux ranged from 0.40 μmol m−2 s−1 in the dry period to 1.93 μmol m−2 s−1 in the growing season. Soil CO2 efflux showed a large spatial variability, with different behaviour between the measured periods. Whereas in the dry period differences among ecosystems were larger (CVs 75-80%) than within them (CVs 40-55%), in the growing season the CVs were smaller (40-50%) and no differences were observed between or within ecosystem. The factors controlling soil CO2 efflux also differed in the two measurement occasions. Whereas in the dry period soil CO2 efflux was mainly the result of transport processes in the soil and therefore related to local factors (OC content, CN ratio, clay, rock outcrop, etc.) assigned to ecosystem conditions, in the growing season soil CO2 efflux was dominated by soil CO2 production and thus related only to organic carbon content and plant cover. In the growing season environmental variables explained ca. 10% of the variation in soil CO2 efflux. In order to capture these different processes in different times of the year, i.e., diffusion versus production processes we calculated a new index, normalised seasonal difference in soil respiration (SDSR), which is proposed as a good indicator of the state and functioning of the ecosystem. 相似文献
19.
This study aims to assess the effects of corrections for disturbances such as an increased amount of dead roots and an increase
in volumetric soil water content on the calculation of soil CO2 efflux partitioning. Soil CO2 efflux, soil temperature and superficial soil water content were monitored in two young beech sites (H1 and H2) during a
trenching experiment. Trenching induced a significant input of dead root mass that participated in soil CO2 efflux and reduced the soil dissolved organic carbon content, while it increased superficial soil water content within the
trenched plot. Annual soil CO2 efflux in control plots was 528 g C m−2 year−1 at H1 and 527 g C m−2 year−1 at H2. The annual soil CO2 efflux in trenched plots was 353 g C m−2 year−1 at H1 and 425 g C m−2 year−1 at H2. By taking into account annual CO2 efflux from decaying trenched roots, the autotrophic contribution to total soil CO2 efflux reached 69% at H1 and 54% at H2. The partitioning calculation was highly sensitive to the initial root mass estimated
within the trenched plots. Uncertainties in the remaining root mass, the fraction of root C that is incorporated into soil
organic matter during root decomposition, and the root decomposition rate constant had a limited impact on the partitioning
calculation. Corrections for differences in superficial soil water content had a significant impact on annual respired CO2 despite a limited effect on partitioning. 相似文献
20.
Currently, it is unknown what role tropical forest soils will play in the future global carbon cycle under higher temperatures. Many tropical forests grow on deeply weathered soils and although it is generally accepted that soil carbon decomposition increases with higher temperatures, it is not known whether subsurface carbon pools are particularly responsive to increasing soil temperatures. Carbon dioxide (CO2) diffusing out of soils is an important flux in the global carbon. Although soil CO2 efflux has been the subject of many studies in recent years, it remains difficult to deduct controls of this flux because of the different sources that produce CO2 and because potential environmental controls like soil temperature and soil moisture often covary. Here, we report results of a 5‐year study in which we measured soil CO2 production on two deeply weathered soil types at different depths in an old‐growth tropical wet forest in Costa Rica. Three sites were developed on old river terraces (old alluvium) and the other three were developed on old lava flows (residual). Annual soil CO2 efflux varied between 2.8–3.6 μmol CO2‐C m?2 s?1 (old alluvium) and 3.4–3.9 μmol CO2‐C m?2 s?1 (residual). More than 75% of the CO2 was produced in the upper 0.5 m (including litter layer) and less than 7% originated from the soil below 1 m depth. This low contribution was explained by the lack of water stress in this tropical wet forest which has resulted in very low root biomass below 2 m depth. In the top 0.5 m CO2 production was positively correlated with both temperature and soil moisture; between 0.6 and 2 m depth CO2 production correlated negatively with soil moisture in one soil and positively with photosynthetically active radiation in the other soil type. Below 2 m soil CO2 production strongly increased with increasing temperature. In combination with reduced tree growth that has been shown for this ecosystem, this would be a strong positive feedback to ecosystem warming. 相似文献