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1.
Most soil respiration measurements are conducted during the growing season. In tundra and boreal forest ecosystems, cumulative winter soil CO2 fluxes are reported to be a significant component of their annual carbon budgets. However, little information on winter soil CO2 efflux is known from mid-latitude ecosystems. Therefore, comparing measurements of soil respiration taken annually versus during the growing season will improve the accuracy of ecosystem carbon budgets and the response of soil CO2 efflux to climate changes. In this study we measured winter soil CO2 efflux and its contribution to annual soil respiration for seven ecosystems (three forests: Pinus sylvestris var. mongolica plantation, Larix principis-rupprechtii plantation and Betula platyphylla forest; two shrubs: Rosa bella and Malus baccata; and two meadow grasslands) in a forest-steppe ecotone, north China. Overall mean winter and growing season soil CO2 effluxes were 0.15-0.26 μmol m−2 s−1 and 2.65-4.61 μmol m−2 s−1, respectively, with significant differences in the growing season among the different ecosystems. Annual Q10 (increased soil respiration rate per 10 °C increase in temperature) was generally higher than the growing season Q10. Soil water content accounted for 84% of the variations in growing season Q10 and soil temperature range explained 88% of the variation in annual Q10. Soil organic carbon density to 30 cm depth was a good surrogate for SR10 (basal soil respiration at a reference temperature of 10 °C). Annual soil CO2 efflux ranged from 394.76 g C m−2 to 973.18 g C m−2 using observed ecosystem-specific response equations between soil respiration and soil temperature. Estimates ranged from 424.90 g C m−2 to 784.73 g C m−2 by interpolating measured soil respiration between sampling dates for every day of the year and then computing the sum to obtain the annual value. The contributions of winter soil CO2 efflux to annual soil respiration were 3.48-7.30% and 4.92-7.83% using interpolated and modeled methods, respectively. Our results indicate that in mid-latitude ecosystems, soil CO2 efflux continues throughout the winter and winter soil respiration is an important component of annual CO2 efflux.  相似文献   

2.
Nitrogen (N) deposition to semiarid ecosystems is increasing globally, yet few studies have investigated the ecological consequences of N enrichment in these ecosystems. Furthermore, soil CO2 flux – including plant root and microbial respiration – is a key feedback to ecosystem carbon (C) cycling that links ecosystem processes to climate, yet few studies have investigated the effects of N enrichment on belowground processes in water-limited ecosystems. In this study, we conducted two-level N addition experiments to investigate the effects of N enrichment on microbial and root respiration in a grassland ecosystem on the Loess Plateau in northwestern China. Two years of high N additions (9.2 g N m−2 y−1) significantly increased soil CO2 flux, including both microbial and root respiration, particularly during the warm growing season. Low N additions (2.3 g N m−2 y−1) increased microbial respiration during the growing season only, but had no significant effects on root respiration. The annual temperature coefficients (Q10) of soil respiration and microbial respiration ranged from 1.86 to 3.00 and 1.86 to 2.72 respectively, and there was a significant decrease in Q10 between the control and the N treatments during the non-growing season but no difference was found during the growing season. Following nitrogen additions, elevated rates of root respiration were significantly and positively related to root N concentrations and biomass, while elevated rates of microbial respiration were related to soil microbial biomass C (SMBC). The microbial respiration tended to respond more sensitively to N addition, while the root respiration did not have similar response. The different mechanisms of N addition impacts on soil respiration and its components and their sensitivity to temperature identified in this study may facilitate the simulation and prediction of C cycling and storage in semiarid grasslands under future scenarios of global change.  相似文献   

3.
Extensive research has focused on the temperature sensitivity of soil respiration. However, in Mediterranean ecosystems, soil respiration may have a pulsed response to precipitation events, especially during prolonged dry periods. Here, we investigate temporal variations in soil respiration (Rs), soil temperature (T) and soil water content (SWC) under three different land uses (a forest area, an abandoned agricultural field and a rainfed olive grove) in a dry Mediterranean area of southeast Spain, and evaluate the relative importance of soil temperature and water content as predictors of Rs. We hypothesize that soil moisture content, rather than soil temperature, becomes the major factor controlling CO2 efflux rates in this Mediterranean ecosystem during the summer dry season. Soil CO2 efflux was measured monthly between January 2006 and December 2007 using a portable soil respiration instrument fitted with a soil respiration chamber (LI-6400-09). Mean annual soil respiration rates were 2.06 ± 0.07, 1.71 ± 0.09, and 1.12 ± 0.12 μmol m−2 s−1 in the forest, abandoned field and olive grove, respectively. Rs was largely controlled by soil temperature above a soil water content threshold value of 10% at 0-15 cm depth for forest and olive grove, and 15% for abandoned field. However, below those thresholds Rs was controlled by soil moisture. Exponential and linear models adequately described Rs responses to environmental variables during the growing and dry seasons. Models combining abiotic (soil temperature and soil rewetting index) and biotic factors (above-ground biomass index and/or distance from the nearest tree) explained between 39 and 73% of the temporal variability of Rs in the forest and olive grove. However, in the abandoned field, a single variable - either soil temperature (growing season) or rewetting index (dry season) - was sufficient to explain between 51 and 63% of the soil CO2 efflux. The fact that the rewetting index, rather than soil water content, became the major factor controlling soil CO2 efflux rates during the prolonged summer drought emphasizes the need to quantify the effects of rain pulses in estimates of net annual carbon fluxes from soil in Mediterranean ecosystems.  相似文献   

4.
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   

5.
《Applied soil ecology》2001,16(3):243-249
Very little is known about the effect of overgrazing on carbon loss from soil in semi-arid savannas and woodlands of South America. Soil carbon parameters were measured in a 10,000 ha restoration project in the western Chaco of Argentina (24°43′S and 63°17′W). Three situations were compared: highly restored (HRS), moderately restored (MRS) and highly degraded (HDS). Soil and litter samples were recovered in the dry and wet seasons. SOC and CO2–C values decreased from the HRS (7.0 kg m−2 and 130 g m−2) to the HDS (1.5 kg m−2 and 46 g m−2) whereas the C mineralization rate increased toward the less restored sites (0.96–2.29). Surface-litter C was similar in both sites under restoration (260 and 229 g m−2), being non-existent at the HDS. Leaves from woody species dominated surface-litter in the HRS, whereas grass material was predominant in the MRS. During the wet season, the SOC decreased, whereas both CO2–C and C mineralization rate increased. The magnitude of the between-season differences was highest at the HDS (62% in SOC, 55% in CO2, and 80% in C mineralization rate). We estimated that C loss since introduction of cattle into the forest was 58 Mg ha−1, reaching a total of 2×1015 g at for the entire Chaco. These values are higher than those caused by the conversion of savannas and other ecosystems into agriculture or cultivated pastures. The amount of C fixed in the highly restored site (275 g ha−1 per year) indicates that the Chaco soils have a significant potential as atmospheric carbon sinks.  相似文献   

6.
Temporal and spatial variability of soil respiration (Rs) was measured and analyzed in a 74-year-old, mixedwood, boreal forest in Ontario, Canada, over a period of 2 years (August 2003–July 2005). The ranges of Rs measured during the two study years were 0.5–6.9 μmol CO2 m−2 s−1 for 2003–2004 (Year 1) and 0.4–6.8 μmol CO2 m−2 s−1 for 2004–2005 (Year 2). Mean annual Rs for the stand was the same for both years, 2.7 μmol CO2 m−2 s−1. Temporal variability of Rs was controlled mainly by soil temperature (Ts), but soil moisture had a confounding effect on Ts. Annual estimates of total soil CO2 emissions at the site, calculated using a simple empirical Rs–Ts relationship, showed that Rs can account for about 88 ± 27% of total annual ecosystem respiration at the site. The majority of soil CO2 emissions came from the upper 12 to 20 cm organic LFH (litter–fibric–humic) soil layer. The degree of spatial variability in Rs, along the measured transect, was seasonal and followed the seasonal trend of mean Rs: increasing through the growing season and converging to a minimum in winter (coefficient of variation (CV) ranged from 4 to 74% in Year 1 and 4 to 62% in Year 2). Spatial variability in Rs was found to be negatively related to spatial variability in the C:N ratio of the LHF layer at the site. Spatial variability in Rs was also found to depend on forest tree species composition within the stand. Rs was about 15% higher in a broadleaf deciduous tree patch compared to evergreen coniferous area. However, the difference was not always significant (at 95% CI). In general, Rs in the mixedwood patch, having both deciduous and coniferous species, was dominated by broadleaf trees, reflecting changing physiological controls on Rs with seasons. Our results highlight the importance of discerning soil CO2 emissions at a variety of spatial and temporal scales. They also suggest including the LFH soil layer and allowing for seasonal variability in CO2 production within that layer, when modeling soil respiration in forest ecosystems.  相似文献   

7.
《Soil biology & biochemistry》2001,33(7-8):1103-1111
Biologically active fractions of soil organic matter are important in understanding decomposition potential of organic materials, nutrient cycling dynamics, and biophysical manipulation of soil structure. We evaluated the quantitative relationships among potential C and net N mineralization, soil microbial biomass C (SMBC), and soil organic C (SOC) under four contrasting climatic conditions. Mean SOC values were 28±11 mg g−1 (n=24) in a frigid–dry region (Alberta/British Columbia), 25±5 mg g−1 (n=12) in a frigid–wet region (Maine), 11±4 mg g−1 (n=117) in a thermic–dry region (Texas), and 12±5 mg g−1 (n=131) in a thermic–wet region (Georgia). Higher mean annual temperature resulted in consistently greater basal soil respiration (1.7 vs 0.8 mg CO2–C g−1 SOC d−1 in the thermic compared with the frigid regions, P<0.001), greater net N mineralization (2.8 vs 1.3 mg inorganic N g−1 SOC 24 d−1, P<0.001), and greater SMBC (53 vs 21 mg SMBC g−1 SOC, P<0.001). Specific respiratory activity of SMBC was, however, consistently lower in the thermic than in the frigid regions (29 vs 34 mg CO2–C g−1 SMBC d−1, P<0.01). Higher mean annual precipitation resulted in consistently lower basal soil respiration (1.1 vs 1.3 mg CO2–C g−1 SOC d−1 in the wet compared with the dry regions, P<0.01) and lower SMBC (31 vs 43 mg SMBC g−1 SOC, P<0.001), but had inconsistent effects on net N mineralization that depended upon temperature regime. Specific respiratory activity of SMBC was consistently greater in the wet than the dry regions (≈33 vs 29 mg CO2–C g−1 SMBC d−1, P<0.01). Although the thermic regions were not able to retain as high a level of SOC as the frigid regions, due likely to high annual decomposition rates, biologically active soil fractions were as high per mass of soil and even 2–3-times greater per unit of SOC in the thermic compared with the frigid regions. These results suggest that macroclimate has a large impact on the portion of soil organic matter that is potentially active, but a relatively small impact on the specific respiratory activity of SMBC.  相似文献   

8.
Spatial and temporal patterns of soil respiration rates and controlling factors were investigated in three wet arctic tundra systems. In situ summer season carbon dioxide fluxes were measured across a range of micro-topographic positions in tussock tundra, wet sedge tundra, and low-centre polygonal tundra, at two different latitudes on the Taimyr Peninsular, central Siberia. Measurements were carried out by means of a multi-channel gas exchange system operating in continuous-flow mode.Measured soil respiration rates ranged from 0.1 g CO2-C m?2 d?1 to 3.9 g CO2-C m?2 d?1 and rate differences between neighbouring sites in the micro-topography (microsites) were larger than those observed between different tundra systems. Statistical analysis identified position of the water table and soil temperature at shallow depths to be common controls of soil respiration rates across all microsites, with each of these two factors explaining high proportions of the observed variations.Modelling of the response of soil respiration to soil temperature and water table for individual microsites revealed systematic differences in the response to the controlling factors between wet and drier microsites. Wet microsites – with a water table position close to the soil surface during most of the summer – showed large soil respiration rate changes with fluctuations of the water table compared to drier microsites. Wet microsites also showed consistently higher temperature sensitivity and a steeper increase of temperature sensitivity with decreasing temperatures than drier sites. Overall, Q10 values ranged from 1.2 to 3.4. The concept of substrate availability for determining temperature sensitivity is applied to reconcile these systematic differences. The results highlight that soil respiration rates in wet tundra are foremost controlled by water table and only secondarily by soil temperature. Wet sites have a larger potential for changes in soil respiration rates under changing environmental conditions, compared to drier sites.It is concluded that understanding and forecasting gaseous carbon losses from arctic tundra soils and its implication for ecosystem-scale CO2 fluxes and soil organic matter dynamics require good knowledge about temporal and spatial patterns of soil water conditions. The water status of tundra soils can serve as a control on the temperature sensitivity of soil respiration.  相似文献   

9.
The contribution of old soil C (SOM) to total soil respiration (RS) in forest has been a crucial topic in global change research, but remains uncertain. Isotopic methods, such as natural variations in carbon isotope composition (δ13C) of soil respiration, are more frequently being applied, and show promise in separating heterotrophic and autotrophic contributions to RS. However, natural and artificial modification of δ13CRs can cause isotopic disequilibria in the soil-atmosphere system generating a mismatch between what is usually measured and what process-based models will predict. Here we report the partitioning of the soil surface CO2 flux in a warm Mediterranean forest into components derived from root, litter/humus, and SOM sources using a new, three end-member mixing model, and compare this with the conventional partitioning into autotrophic and heterotrophic components. The three end-member mixing model takes into account both the discrimination during CO2 respiration/decomposition of the three components, as well as the fractions of their CO2 fluxes integrated over the total soil profile mass. In addition, we used a novel dual-chamber technique to ensure that δ13CRs was subjected to minimal artefacts during measurement.We observed that by using measured soil surface CO2 concentrations as a baseline level for the dual-chamber operation, it was possible to achieve and monitor the necessary conservation of the soil CO2 steady-state diffusion conditions during the measurements, without using permanent collars inserted deeply into the soil. When RS (8.64 g CO2 m2 d−1) was partitioned into two components, the mean autotrophic and heterotrophic respiration was 56 and 44%, respectively. When RS was partitioned using the three-way model, however, roots, litter/humus, and SOM contributed 30, 33, and 37% of the total flux. Our results confirm that to improve the estimates of the partitioning method, it is important to distinguish the fractional contribution of the long-term SOM-derived flux from younger and more labile sources.  相似文献   

10.
《Soil biology & biochemistry》2001,33(12-13):1581-1589
The activity and biomass of soil microorganisms were measured in soils from 25 different arable sites in the Pacific region of Nicaragua with the objective of elucidating their interrelationship with soil textural and soil chemical properties. All soils developed from recent volcanic deposits but differ in their particle size distribution. Short-term phosphorus fixation capacity varied widely and was, on average, 11% of added P. In contrast, long-term P fixation capacity varied within a small range of around 55%. Mean basal respiration was 8.6 μg CO2–C d−1 g−1 soil, average contents of biomass C, biomass P, and ergosterol as an indicator of fungal biomass were 116, 1.95, and 0.34 μg g−1 soil, respectively. They were all, except biomass P, significantly lower in the sandy than in the loamy soils. The mean biomass C-to-soil C ratio was 0.69%, the mean metabolic quotient 95 mg CO2–C d−1 g−1 biomass C, the mean ergosterol-to-biomass C ratio 0.31% and the mean biomass C-to-P ratio 107. The very low ergosterol-to-biomass C ratio indicates that fungi contribute only a relatively small percentage to the microbial biomass. The biomass C-to-P ratio exceeded considerably the soil C-to-total P ratio. Metabolic quotient qCO2 and ergosterol-to-biomass C were both negatively correlated with biomass C-to-soil C ratio and clay content, indicating positive correlations between qCO2 and ergosterol-to-biomass C ratio and between biomass C-to-soil C ratio and clay content. Key problems of soil fertility and soil quality in Nicaragua are low availability of soil organic matter and phosphorus to soil microorganisms, which are magnified by a low percentage of fungi, probably reducing the ability of soil to provide nutrients for plant growth.  相似文献   

11.
We studied a semi-natural forest in Northern Italy that was set aside more than 50 years ago, in order to better understand the soil carbon cycle and in particular the partitioning of soil respiration between autotrophic and heterotrophic respiration. Here we report on soil organic carbon, root density, and estimates of annual fluxes of soil CO2 as measured with a mobile chamber system at 16 permanent collars about monthly during the course of a year. We partitioned between autotrophic and heterotrophic respiration by the indirect regression method, which enabled us to obtain the seasonal pattern of single components.The soil pool of organic carbon, with 15.8 (±4.5) kg m?2, was very high over the entire depth of 45 cm. The annual respiration rates ranged from 0.6 to 6.9 μmol CO2 m?2 s?1 with an average value of 3.4 (±2.3) μmol CO2 m?2 s?1, and a cumulative flux of 1.1 kg C m?2 yr?1. The heterotrophic component accounted for 66% of annual CO2 efflux. Soil temperature largely controlled the heterotrophic respiration (R2 = 0.93), while the autotrophic component followed irradiation, pointing to the role of photosynthesis in modulating the annual course of soil respiration.Most studies on soil respiration partitioning indicate autotrophic root respiration as a first control of the spatial variability of the overall respiration, which originates mainly from the uppermost soil layers. Instead, in our forest the spatial variability of soil respiration was mainly linked to soil carbon, and deeper layers seemed to provide a significant contribution to soil respiration, a feature that may be typical for an undisturbed, naturally maturing ecosystem with well developed pedobiological processes and high carbon stocks.  相似文献   

12.
Underestimation of nocturnal CO2 respiration using the eddy covariance method under calm conditions remains an unsolved problem at many flux observation sites in forests. To evaluate nocturnal CO2 exchange in a Japanese cypress forest, we observed CO2 flux above the canopy (Fc), changes in CO2 storage in the canopy (St) and soil, and trunk and foliar respiration for 2 years (2003–2004). We scaled these chamber data to the soil, trunk, and foliar respiration per unit of ground area (Fs, Ft, Ff, respectively) and used the relationships of Fs, Ft, and Ff with air or soil temperature for comparison with canopy-scale CO2 exchange measurements (=Fc + St). The annual average Fs, Ft, and Ff were 714 g C m−2 year−1, 170 g C m−2 year−1, and 575 g C m−2 year−1, respectively. At small friction velocity (u*), nocturnal Fc + St was smaller than Fs + Ft + Ff estimated using the chamber method, whereas the two values were almost the same at large u*. We replaced Fc + St measured during calm nocturnal periods with a value simulated using a temperature response function derived during well-mixed nocturnal periods. With this correction, the estimated net ecosystem exchange (NEE) from Fc + St data ranged from −713 g C m−2 year−1 to −412 g C m−2 year−1 in 2003 and from −883 g C m−2 year−1 to −603 g C m−2 year−1 in 2004, depending on the u* threshold. When we replaced all nocturnal Fc + St data with Fs + Ft + Ff estimated using the chamber method, NEE was −506 g C m−2 year−1 and −682 g C m−2 year−1 for 2003 and 2004, respectively.  相似文献   

13.
Soil respiration is an important carbon (C) flux of global C cycle, and greatly affected by nitrogen (N) addition in the form of deposition or fertilization. However, the effects of N addition on the different components of soil respiration are poorly understood. The aim of this study is to investigate how the components of soil respiration response to N addition and the potential mechanisms in a subtropical bamboo ecosystem. Four N treatment levels (0, 50, 150, 300 kg N ha−1 year−1) were applied monthly in a Pleioblastus amarus bamboo plantation since November 2007. Total soil respiration (RST) and soil respiration derived from litter layer (RSL), root-free soil (RSS), and plant roots (RSR) were measured for one year (February 2010 to January 2011). The results showed that the mean rate of RST was 428 ± 11 g C m−2 year−1, and RSL, RSS, RSR contributed (30.2 ± 0.7)%, (20.7 ± 0.9)%, and (49.1 ± 0.7)%, respectively. The temperature coefficients (Q10) of RST, RSL, RSS, and RSR were 2.87, 2.28, 3.09, and 3.19, respectively, in control plots. Nitrogen additions significantly increased RST and its three components. RSR was stimulated by N additions through increasing fine root biomass and root metabolic rate. The positive effects of N additions on soil fertility, microbial activity, and the quality and amount of aboveground litterfall also stimulated other CO2 production processes. In the background of increased N input, response of RST and components of RST are primarily due to the positive response of plant growth in this bamboo ecosystem.  相似文献   

14.
Forest ecosystems on the Loess Plateau are receiving increasing attention for their special importance in carbon fixation and conservation of soil and water in the region. Soil respiration was investigated in two typical forest stands of the forest-grassland transition zone in the region, an exotic black locust (Robinia pseudoacacia) plantation and an indigenous oak (Quercus liaotungensis) forest, in response to rain events (27.7 mm in May 2009 and 19 mm in May 2010) during the early summer dry season. In both ecosystems, precipitation significantly increased soil moisture, decreased soil temperature, and accelerated soil respiration. The peak values of soil respiration were 4.8 and 4.4 μmol CO2 m−2 s−1 in the oak plot and the black locust plot, respectively. In the dry period after rainfall, the soil moisture and respiration rate gradually decreased and the soil temperature increased. Soil respiration rate in black locust stand was consistently less than that in oak stand, being consistent with the differences in C, N contents and fine root mass on the forest floor and in soil between the two stands. However, root respiration (Rr) per unit fine root mass and microbial respiration (Rm) per unit the amount of soil organic matter were higher in black locust stand than in oak stand. Respiration by root rhizosphere in black locust stand was the dominant component resulting in total respiration changes, whereas respiration by roots and soil microbes contributed equally in oak stand. Soil respiration in the black locust plantation showed higher sensitivity to precipitation than that in the oak forest.  相似文献   

15.
We used natural gradients in soil and vegetation δ13C signatures in a savannah ecosystem in Texas to partition soil respiration into the autotrophic (Ra) and heterotrophic (Rh) components. We measured soil respiration along short transects from under clusters of C3 trees into the C4 dominated grassland. The site chosen for the study was experiencing a prolonged drought, so an irrigation treatment was applied at two positions of each transect. Soil surface CO2 efflux was measured along transects and CO2 collected for analysis of the δ13C signature in order to: (i) determine how soil respiration rates varied along transects and were affected by localised change in soil moisture and (ii) partition the soil surface CO2 efflux into Ra and Rh, which required measurement of the δ13C signature of root- and soil-derived CO2 for use in a mass balance model.The soil at the site was unusually dry, with mean volumetric soil water content of 8.2%. Soil respiration rates were fastest in the centre of the tree cluster (1.5 ± 0.18 μmol m?2 s?1; mean ± SE) and slowest at the cluster–grassland transition (0.6 ± 0.12 μmol m?2 s?1). Irrigation produced a 7–11 fold increase in the soil respiration rate. There were no significant differences (p > 0.5) between the δ13C signature of root biomass and respired CO2, but differences (p < 0.01) were observed between the respired CO2 and soil when sampled at the edge of the clusters and in the grassland. Therefore, end member values were measured by root and soil incubations, with times kept constant at 30 min for roots and 2 h for soils. The δ13C signature of the soil surface CO2 efflux and the two end member values were used to calculate that, in the irrigated soils, Rh comprised 51 ± 13.5% of the soil surface CO2 efflux at the mid canopy position and 57 ± 7.4% at the drip line. In non-irrigated soil it was not possible to partition soil respiration, because the δ13C signature of the soil surface CO2 efflux was enriched compared to both the end member values. This was probably due to a combination of the very dry porous soils at our study site (which may have been particularly susceptible to ingress of atmospheric CO2) and the very slow respiration rates of the non-irrigated soils.  相似文献   

16.
《Pedobiologia》2014,57(4-6):263-269
Nitrogen (N) availability is an important factor that determines ecosystem productivity and respiration, especially in N-limited alpine ecosystems. However, the magnitude of this response depends on the timing and amounts of N input. Moreover, we have only a limited understanding of the potential effects of the timing of N fertilization on ecosystem carbon (C) and N processes, and activities of the soil microbes. A nitrogen fertilization experiment was conducted in an alpine meadow on the Tibetan Plateau to determine how plant productivity and ecosystem respiration (RE) respond to the timing and amount of N application. In this study, half of the N was added either in the early spring (ES), before the growing season, or in the late fall (LF), after the growing season. All treatments received the other half of the N in mid-July. Three N levels (10, 20, 40 kg N hm−2 yr−1) were used for each of two N treatments, with no N addition used as a control. Plant aboveground biomass, ecosystem respiration (RE) and soil respiration (RS) were measured for the 2011 and 2012 growing seasons. The LF treatment enhanced ecosystem CO2 efflux compared with the ES treatment at high N addition levels, resulting from an increase of soil dissolved organic C (DOC) and soil microbial activity. The ES treatment resulted in increased plant aboveground biomass when compared with LF during both growing seasons, although this increase accounted for little variation in ecosystem and soil respiration. Overall, the ES treatment is likely to increase the ecosystem C pool, while the LF treatment could accelerate ecosystem C cycling, especially for the high N treatment. Our results suggest that supplying N during the early stage of the growing season benefits both forage production and soil C sequestration in this alpine ecosystem.  相似文献   

17.
《Soil biology & biochemistry》2001,33(4-5):503-509
The distribution of vegetation types in Venezuelan Guyana (in the ‘Canaima’ National Park) represents a transitional stage in a long term process of savannization, a process considered to be conditioned by a combined chemical and intermittent drought stress. All types of woody vegetation in this environment accumulate large amounts of litter and soil organic carbon (SOC). We hypothesized that this accumulation is caused by low microbial activity. During 1 year we measured microbial biomass carbon (Cmic), microbial respiration and soil respiration of stony Oxisols (Acrohumox) at a tall, a medium and a low forest and with three chemical modifications of site conditions by the addition of NO3−, Ca2+ and PO43− as possible limiting elements. Due to high SOC contents, mean Cmic was 1 mg g soil−1 in the mineral topsoil and 3 mg g soil−1 in the forest floor. Mean microbial respiration in the mineral topsoil and the forest floor were 165 and 192 μg CO2-C g soil−1 d−1, respectively. We calculated high mean metabolic quotients (qCO2) of 200 mg CO2-C g Cmic−1 d−1 in the litter layer and 166 mg CO2-C g Cmic−1 d−1 in the mineral topsoil, while the Cmic-to-SOC ratios were as low as 1.0% in the litter layer and 0.8% in the mineral topsoil. Annual soil respiration was 9, 12 and 10 Mg CO2-C ha−1 yr−1 in the tall, medium and low forest, respectively. CO2 production was significantly increased by CaHPO4 fertilization, but no consistent effects were caused by Ca2+ and NO3−, fertilization. Our findings indicate that Cmic and microbial respiration are reduced by low nutrient concentrations and low litter and SOC quality. Reduced microbial decomposition may have contributed to SOC accumulation in these forests.  相似文献   

18.
The aim of this study was to measure the in situ soil CO2 flux from grassland, afforested land and reclaimed coalmine overburden dumps by using the automated soil CO2 flux system (LICOR‐8100® infrared gas analyzer, LICOR Inc., Lincoln, NE). The highest soil CO2 flux was observed in natural grassland (11·16 µmol CO2 m−2s−1), whereas the flux was reduced by 38 and 59 per cent in mowed site and at 15‐cm depth, respectively. The flux from afforested area was found 5·70 µmol CO2 m−2s−1, which is 50 per cent lower than natural grassland. In the reclaimed coalmine overburden dumps, the average flux under tree plantation was found to be lowest in winter and summer (0·89–1·12 µmol CO2 m−2s−1) and highest during late monsoon (3–3·5 µmol CO2 m−2s−1). During late monsoon, the moisture content was found to be higher (6–7·5 per cent), which leads to higher microbial activity and decomposition. In the same area under grass cover, soil CO2 flux was found to be higher (8·94 µmol CO2 m−2s−1) compared with tree plantation areas because of higher root respiration and microbial activity. The rate of CO2 flux was found to be determined predominantly by soil moisture and soil temperature. Our study indicates that the forest ecosystem plays a crucial role in combating global warming than grassland; however, to reduce CO2 flux from grassland, mowing is necessary. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

19.
Partitioning the soil surface CO2 flux (RS) flux is an important step in understanding ecosystem-level carbon cycling, given that RS is poorly constrained and its source components may have different sensitivities to climate change. Trenched plots are an inexpensive but labor-intensive method of separating the RS flux into its root (autotrophic) and soil (heterotrophic) components. This study tested if various methods of plant suppression in trenched plots affected RS fluxes, quantified the RS response to soil temperature and moisture changes, and estimated the heterotrophic contribution to RS. It was performed in a boreal black spruce (Picea mariana) plantation, using a randomized complete block design, during the 2007 and 2008 growing seasons. Trenched plots had significantly lower RS than control plots, with differences appearing ∼100 days after trenching; spatial variability doubled immediately after trenching but then declined throughout the experiment. Most trenching treatments had significantly lower (by ∼0.5 μmol CO2 m−2 s−1) RS than the controls, and there was no significant difference in RS among the various trenching treatments. Soil temperature at 2 cm explained more RS variability than did 10-cm temperature or soil moisture. Temperature sensitivity (Q10) declined in the control plots from ∼2.6 (at 5 °C) to ∼1.6 (at 15 °C); trenched plots values were higher, from 3.1 at 5 °C to 1.9 at 15 °C. We estimated RS for the study period to be 241 ± 40 g C m−2, with live roots contributing 64% of RS after accounting for fine root decay, and 293 g C m−2 for the entire year. These findings suggest that laborious hand weeding of trenched plot vegetation may be replaced by other methods, facilitating future studies of this large and poorly-understood carbon flux.  相似文献   

20.
Continuous half-hourly measurements of soil (Rs) and bole respiration (Rb), as well as whole-ecosystem CO2 exchange, were made with a non steady-state automated chamber system and with the eddy covariance (EC) technique, respectively, in a mature trembling aspen stand between January 2001 and December 2003. Our main objective was to investigate the influence of long-term variations of environmental and biological variables on component-specific and whole-ecosystem respiration (Re) processes. During the study period, the stand was exposed to severe drought conditions that affected much of the western plains of North America. Over the 3 years, daily mean Rs varied from a minimum of 0.1 μmol m−2 s−1 during winter to a maximum of 9.2 μmol m−2 s−1 in mid-summer. Seasonal variations of Rs were highly correlated with variations of soil temperature (Ts) and water content (θ) in the surface soil layers. Both variables explained 96, 95 and 90% of the variance in daily mean Rs from 2001 to 2003. Aspen daily mean Rb varied from negligible during winter to a maximum of 2.5 μmol m−2 bark s−1 (2.2 μmol m−2 ground s−1) during the growing season. Maximum Rb occurred at the end of the aspen radial growth increment and leaf emergence period during each year. This was 2 months before the peak in bole temperature (Tb) in 2001 and 2003. Nonetheless, Rb was highly correlated with Tb and this variable explained 77, 87 and 62% of the variance in Rb in the respective years. Partitioning of Rb between its maintenance (Rbm) and growth (Rbg) components using the mature tissue method showed that daily mean Rbg occurred at the same time as aspen radial growth increment during each growing season. This method led, however, to systematic over- and underestimations of Rbm and Rbg, respectively, during each year. Annual totals of Rs, Rb and estimated foliage respiration (Rf) from hazelnut and aspen trees were, on average, 829, 159 and 202 g C m−2 year−1, respectively, over the 3 years. These totals corresponded to 70, 14 and 16%, respectively, of scaled-up respiration estimates of Re from chamber measurements. Scaled Re estimates were 25% higher (1190 g C m−2 year−1) than the annual totals of Re obtained from EC (949 g C m−2 year−1). The independent effects of temperature and drought on annual totals of Re and its components were difficult to separate because the two variables co-varied during the 3 years. However, recalculation of annual totals of Rs to remove the limitations imposed by low θ, suggests that drought played a more important role than temperature in explaining interannual variations of Rs and Re.  相似文献   

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