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1.
Thermal analysis techniques have been used to differentiate soil organic carbon (SOC) pools with differing thermal stability. A correlation between thermal and biological stability has been indicated in some studies, while others reported inconsistent relationships. Despite these controversial findings and no standardized method, several recently published studies used thermal analysis techniques to determine the biological stability and quality of SOC in mineral soils. This study examined whether thermal oxidation at temperature levels between 200°C and 400°C, combined with evolving gas analysis and isotope ratio mass spectrometry, is capable of identifying SOC pools with differing biological stability in mineral soils. Soil samples from three sites being under Miscanthus (C4‐plant) cultivation for more than 17 years following former agricultural cropland (only C3‐plant) cultivation were used. Due to natural shifts in 13C content, young and labile Miscanthus‐derived SOC could be distinguished from stable and old C3‐plant‐derived SOC. The proportion of Miscanthus‐derived SOC increased significantly with increasing temperatures up to 350°C in bulk soil samples, indicating increasing oxidation of labile and young SOC with increasing temperatures. Use of density fractions to validate the thermally oxidized SOC from bulk soil samples revealed that the thermal oxidation patterns did not reflect the biological stability of SOC. The suggested biologically labile particulate organic carbon (light fraction from density fractionation) was clearly enriched in Miscanthus‐derived young SOC. The thermal oxidation patterns, however, revealed preferential oxidation of these biologically labile fractions not at low temperatures, but rather at higher temperatures. The reverse was found for the biologically stable mineral‐associated density fraction (heavy fraction). Based on different soil types, it was concluded that the thermal stability of SOC between 200°C and 400°C is not a suitable indicator of the biological stability of SOC and, thus, thermal oxidation is not capable of fractionating SOC pools with differing biological stability.  相似文献   

2.
To investigate the effect of soil physical conditions and land use on emissions of nitrous oxide (N2O) to the atmosphere, soil cores of an imperfectly drained gleysol were taken from adjacent fields under perennial ryegrass and winter wheat. The cores were fertilized with ammonium nitrate and incubated at three different temperatures and water‐filled pore space (WFPS) values, and N2O emissions were measured by gas chromatography. Emissions showed a very large response to temperature. Apparent values of Q10 (emission rate at (T + 10)°C/emission rate at T°C) for the arable soil were about 50 for the 5–12°C interval and 8.9 for 12–18°C; the corresponding Q10s for the grassland soil were 3.7 and 2.3. Emissions from the grassland soil were always greater than those from the arable soil, although the ratio narrowed with increasing temperature. Changes in soil WFPS also had a profound effect on emissions. Those from the arable soil increased about 30‐fold as the WFPS increased from 60 to 80%, while that from the grassland soil increased 12‐fold. This latter response was similar to earlier field measurements. The N2O emissions were considered to be produced primarily by denitrification. We concluded that the impacts of temperature and WFPS on emissions could both be explained on the basis of existing models relating increasing respiration or decreased oxygen diffusivity, or both, to the development of anaerobic zones within the soil.  相似文献   

3.
Emissions of nitrous oxide (N2O), a potent greenhouse gas, from agricultural soil have been recognized to be affected by nitrogen (N) application and temperature. Most of the previous studies were carried out to determine effects of temperature on N2O emissions at a fixed N application rate or those of N application rates at a specific temperature. Knowledge about the effects of different ammonium (NH4+) application rates and temperatures on N2O emissions from tropical agricultural soil and their interactions is limited. Five grams of air-dried sandy loam soil, collected in Central Vietnam, were adjusted to 0, 400, 800 and 1200 mg NH4-N kg–1 soil (abbreviated as 0 N, 400 N, 800 N and 1200 N, respectively) at 60% water holding capacity were aerobically incubated at 20°C, 25°C, 30°C or 35°C for 28 days. Mineral N contents and N2O emission rates were determined on days 1, 3, 5, 7, 14, 21 and 28. Cumulative N2O emissions for 28 days increased with increasing NH4+ application rates from 0 to 800 mg N kg–1 and then declined to 1200 mg N kg–1. Cumulative N2O emissions increased in the order of 35°C, 20°C, 30°C and 25°C. This lowest emission at 35°C occurred because N2O production was derived only from autotrophic nitrification while other N2O production processes, e.g., nitrifier denitrification and coupled nitrification-denitrification occurred at lower temperatures. More specifically, cumulative N2O emissions peaked at 800 N and 25°C, and the lowest emissions occurred at 1200 N and 35°C. In conclusion, N2O emissions were not exponentially correlated with NH4+ application rates or temperatures. Higher NH4+ application rates at higher temperatures suppressed N2O emissions.  相似文献   

4.

Purpose

Ecosystem restorations can impact carbon dioxide (CO2) and nitrous oxide (N2O) emissions which are important greenhouse gasses. Alpine meadows are degraded worldwide, but restorations are increasing. Because their soils represent large carbon (C) and nitrogen (N) pools, they may produce significant amounts of CO2 and N2O depending on the plant species used in restorations. In addition, warming and N deposition may impact soil CO2 and N2O emissions from restored meadows.

Materials and methods

We collected soils from degraded meadows and plots restored using three different plant species at Wugong Mountain (Jiangxi, China). We measured CO2 and N2O emissions when soils were incubated at different temperatures (15, 25 or 35 °C) and levels of N addition (control vs. 4 g m?2) to understand their responses to warming and N deposition.

Results and discussion

Dissolved organic C was higher in restored plots (especially with Fimbristylis dichotoma) compared to non-restored bare soils, and their soil inorganic N was lower. CO2 emission rates were increased by vegetation restorations, decreased by N deposition, and increased by warming. CO2 emission rates were similar for the three grass species at 15 and 25 °C, but they were lower with Miscanthus floridulus at 35 °C. Soils from F. dichotoma and Carex chinensis plots had higher N2O emissions than degraded or M. floridulus plots, especially at 25 °C.

Conclusions

These results show that the effects of restorations on soil greenhouse gas emissions depended on plant species. In addition, these differences varied with temperature suggesting that future climate should be considered when choosing plant species in restorations to predict soil CO2 and N2O emissions and global warming potential.
  相似文献   

5.
Spatial variability in exponential mean soil temperature for a full year in a newly planted forest in northern England was examined using the sucrose inversion method of temperature measurement. The exponential mean temperature decreased significantly with soil depth (P < 0.001). The rate of this decrease varied significantly between different areas of the forest with slightly different soil profiles (0.001 < P < 0.01). Exponential means for 30–50cm depth in the forest and comparable arithmetic means for the nearest meteorological stations were similar. Exponential mean temperatures at 5 cm soil depth were, on average, 1.5° higher in the ridges than in the adjacent flat areas (P < 0.001). The exponential mean for the flat areas was, on average, 0.3° higher to the south-west of the ridge than to the north-east (0.001 < P < 0.01). It was also 0.9°C lower than the mean at 5 cm depth in the neighbouring rides (0.001 < P < 0.01).  相似文献   

6.
Soil temperature is a major factor affecting organic matter decomposition and thus, global warming may accelerate decomposition processes. However, it remains unclear whether the effects will be similar in climatically different regions. The effects of soil temperatures of 5, 10 and 15 °C on the decomposition of Scots pine (Pinus sylvestris L.) needles were assessed in a 1-year (360 days) growth chamber experiment. Intact peat cores from two climatically different peatland sites (southern and northern Finland) were used as the incubation environments. Needles were incubated in litter bags beneath the living moss layer, and mass loss and nitrogen (N) concentration were determined at 60-day intervals. The rate of mass loss from the needles over time was clearly lower in the 5 °C treatment than at the higher temperatures. Mass loss was strongly related to the accumulated soil temperature sum. In temperatures higher than 5 °C, mass losses were higher in the northern peat. Also, the limit value of decomposition (asymptotic maximum mass loss) was slightly higher in the northern peat (92%), than in the southern peat (87%). The N concentration increased up to a mass loss of 50–60%, whereupon it decreased, while the amount of N (as a percentage of the original amount) remained unchanged until a mass loss of 50–60%, whereupon it decreased linearly. It seems that increasing soil temperatures may result in slightly higher rates of needle litter mass loss and consequent N release in northern peat than in southern peat. The faster decomposition in higher temperatures in the northern peat, together with the slightly higher maximum mass loss value, imply that with climatic warming, susceptibility of boreal peatlands for becoming sources of carbon to the atmosphere may increase towards north.  相似文献   

7.
For this century, an increasing frequency of extreme meteorological boundary conditions is expected, presumably resulting in a changing frequency of freezing and thawing of soils in higher‐elevation areas. Our current knowledge about the effects of these events on trace‐gas emissions from soils is scarce. In this study, the effects of freeze–thaw events on the fluxes of the trace gases CO2, N2O, and NO between soil and atmosphere were investigated in a laboratory experiment. Undisturbed soil columns were collected from a mature Norway spruce forest in the “Fichtelgebirge”, SE Germany. The influence of freezing temperatures (–3°C, –8°C, –13°C) on gas fluxes was studied during the thawing periods (+5°C) in three freeze–thaw cycles (FTCs) and compared to unfrozen controls (+5°C). Two different types of soil columns were examined in parallel—one consisting of O layer only (O columns) and one composed of O layer and mineral soil horizons (O+M columns)—to quantify the contribution of the organic layer and the top mineral soil to the production or consumption of these trace gases. During the thawing period, we observed increasing emissions of CO2, N2O, and NO from the spruce forest soil, but the cumulative emissions of these gases did mostly not exceed the level of the controls. The results show that the O layers were mainly involved in the gas production. Severe soil frost increased CO2 fluxes during soil thawing, whereas repetition of the freeze–thaw events decreased CO2 fluxes from the thawing soil. Fluxes of N2O and NO were neither influenced by freezing temperature nor by freeze–thaw repetition. Stable‐isotope analysis indicated that denitrification was mostly responsible for the N2O production in the FTC columns. Furthermore, isotope data demonstrated a consumption of N2O through microbial denitrification to N2. It was further shown, that production of N2O also occurred in the mineral horizons. The NO emissions were mainly driven by increasing soil temperature during thawing. In this freeze–thaw experiment up to 20 times higher NO than N2O fluxes were recorded. Our results suggest that topsoil thawing has little potential to increase the emissions of CO2, N2O, and NO in spruce forest soils.  相似文献   

8.
We report on the seasonal responses of soil nitrogen (N) pools to soil warming in a cool temperate forest where mild freeze–thaw cycles occur during winter. Artificial soil warming of 2–5 °C was implemented to prevent freezing, making it possible to evaluate the effects of soil freezing on soil characteristics. At control sites, the dissolved organic N and NH4–N pools were largest in winter. Soil warming decreased these solute pools to 17–25% of control levels during winter, but not in other seasons. These results confirm that soil freezing is the driving force of N dynamics during winter, and is easily lost by a few degrees of warming at this study site. The substantial reduction of solute N pools may reduce N availability in the cool temperate forest.  相似文献   

9.
《Soil biology & biochemistry》2012,44(12):2432-2440
Feedbacks to global warming may cause terrestrial ecosystems to add to anthropogenic CO2 emissions, thus exacerbating climate change. The contribution that soil respiration makes to these terrestrial emissions, particularly from carbon-rich soils such as peatlands, is of significant importance and its response to changing climatic conditions is of considerable debate. We collected intact soil cores from an upland blanket bog situated within the northern Pennines, England, UK and investigated the individual and interactive effects of three primary controls on soil organic matter decomposition: (i) temperature (5, 10 and 15 °C); (ii) moisture (50 and 100% field capacity – FC); and (iii) substrate quality, using increasing depth from the surface (0–10, 10–20 and 20–30 cm) as an analogue for increased recalcitrance of soil organic material. Statistical analysis of the results showed that temperature, moisture and substrate quality all significantly affected rates of peat decomposition. Q10 values indicated that the temperature sensitivity of older/more recalcitrant soil organic matter significantly increased (relative to more labile peat) under reduced soil moisture (50% FC) conditions, but not under 100% FC, suggesting that soil microorganisms decomposing the more recalcitrant soil material preferred more aerated conditions. Radiocarbon analyses revealed that soil decomposers were able to respire older, more recalcitrant soil organic matter and that the source of the material (deduced from the δ13C analyses) subject to decomposition, changed depending on depth in the peat profile.  相似文献   

10.
Forty percentage of UK peatlands have been drained for agricultural use, which has caused serious peat wastage and associated greenhouse gas emissions (carbon dioxide (CO2) and methane (CH4)). In this study, we evaluated potential trade-offs between water-table management practices for minimizing peat wastage and greenhouse gas emissions, while seeking to sustain romaine lettuce production: one of the most economically relevant crop in the East Anglian Fenlands. In a controlled environment experiment, we measured lettuce yield, CO2, CH4 fluxes and dissolved organic carbon (DOC) released from an agricultural fen soil at two temperatures (ambient and +2°C) and three water-table levels (−30 cm, −40 cm and −50 cm below the surface). We showed that increasing the water table from the currently used field level of −50 cm to −40 cm and −30 cm reduced CO2 emissions, did not affect CH4 fluxes, but significantly reduced yield and increased DOC leaching. Warming of 2°C increased both lettuce yield (fresh leaf biomass) and peat decomposition through the loss of carbon as CO2 and DOC. However, there was no difference in the dry leaf biomass between the intermediate (−40 cm) and the low (−50 cm) water table, suggesting that romaine lettuce grown at this higher water level should have similar energetic value as the crop cultivated at −50 cm, representing a possible compromise to decrease peat oxidation and maintain agricultural production.  相似文献   

11.

Purpose

As micronutrients are essential for all living organisms, their availability in forest soils is important to the forest ecosystem. Studying the effect of global warming on the availability of mineral elements is more significant for forest management, but the scarcity of these elements is a concern. This study aims to investigate the responses of soil micronutrient availability to experimental warming in two contrasting forest ecosystems in the Eastern Tibetan Plateau of China.

Materials and methods

Using the open-top chamber (OTC) method simulates the global warming and chemical extractants extract soil micronutrients (CaCl2 and Mehlich-3 extractant for Fe, Mn, Cu, Zn, and with boiling hot water for extracting B) to study the availability of these micronutrients in two contrasting forest ecosystems (a dragon spruce plantation and a natural forest) under experimental warming.

Results and discussion

The results showed that soil temperature in the OTCs was increased by 0.56 and by 0.55 °C in the plantation and the natural forest, respectively. The total and Mehlich-3-extractable Cu, Fe, Mn, and Zn were increased by warming in the plantation (except Mehlich-3-extractable Fe, which decreased slightly) but decreased by warming in the natural forest. The CaCl2-extractable micronutrients were not significantly affected by warming. The retained total B in both the plantation and natural forest was decreased by experimental warming. Either the effect of warming or forest type on these micronutrients varied due to their different associations with soil properties. What is more, the relative impact of forest type was stronger than warming on the soil properties with exception of the soil pH and total B concentration.

Conclusions

Reforestation would generate greater influences on soil environment although it is an important effective action to remain ecologic balance usually. The responses of the total soil micronutrients and their availability to warming depended on the forest type, as their concentration was significantly correlated with the soil water and pH. It was implied that the soil pH and water content are important to the availability of micronutrients in soil and provide managers with important information to better manipulate their forests for tree growth and as wildlife habitats.  相似文献   

12.
ABSTRACT

The response of soil organic matter (SOM) to global warming is a crucial subject. However, the temperature sensitivity of SOM turnover remains largely uncertain. Changes in the mineralization of native SOM, i.e., priming effect (PE) may strongly affect the temperature sensitivity of SOM turnover in the presence of global warming. We investigated the direction and magnitude of the PE in a Japanese volcanic ash soil at different temperatures (15°C, 25°C, and 35°C) using a natural 13C tracer (C4-plant, maize leaf) in a short-term (25 days) incubation study. In addition, we evaluated the temperature sensitivity expressed as Q10 value with and without the addition of maize to the soil and their relations to PE. We found that positive PE occurred at each temperature condition and tended to increase with decreased temperature, and these PE results were consistent with the microbial biomass at the end of the incubation period. CO2 emission from control soil (without maize) increased with increasing temperature (Q10 = 2.6), but CO2 emission from the soil with added maize did not significantly change with increasing temperature (Q10 = 1.0). This was caused by the suppression of CO2 emission from the soil with increasing temperature (Q10 = 0.9). On the other hand, soil-originated CO2 emission clearly increased with increasing temperature (Q10 = 3.4) when Q10 values were calculated on the assumption that the temperature and substrate supply increase at the same time (from 25°C). These results suggest that not only the temperature increase but also the labile carbon supply may be important for the temperature sensitivity of Japanese volcanic ash soil.  相似文献   

13.
A soil climosequence in tussock grasslands in South Island, New Zealand, encompassing climates ranging from cold to warm temperate provided a spatial analogue of climate change for investigating the effects of global warming on soil C contents and turnover. Mean annual temperature (T) and annual precipitation (P) ranged from 2 to 10°C, and 350 to 5000 mm, respectively. Soil C contents were curvilinearly related to T/P across the sequence (r=−0.95, significant at P<0.0l), indicating that east of the Southern Alps, increased decomposition of organic matter with global warming would provide a positive feedback to further increase atmospheric CO2. This decrease in New Zealand's soil C, estimated to be up to 10% of the current content for a global temperature rise of 0.03 K a−1 to 2050, could contribute about 0.5 × 1015 g C to the atmosphere over the next 60 years. These conclusions were generally supported by changes in soil C turnover estimated from ‘bomb’14C enrichment. The unexpectedly slow turnover found for two soils was explained by a ‘memory’ effect from the former southern beech forest that grew on these soils in prehistoric times. Accumulation of Al-humus under the forest may be responsible for the slow C turnover observed.  相似文献   

14.
Global warming has profound effects on the distribution of water and heat in soil. This study aimed to examine the effects of warming on water storage, thermal properties, and heat flux changes at different depth (5–10, 10–20, and 20–40 cm) in a winter wheat (Triticum aestivum L.) field. The experiment with simulated warming, manipulated with infrared heaters, and its control combined with a nitrogen fertilization treatment was conducted in the North China Plain. The results showed that warming of around 2°C at 5 cm soil depth reduced soil water storage by 3.2%-11.1% before the jointing stage. However, the difference in soil water storage between warming and non-warming conditions behaved inversely before and after mid-April. Experimental warming significantly reduced soil volumetric heat capacity and thermal conductivity. In the winter, the warming depressed the upward heat flux by 42.4%-50.1% at the 5–10 cm layer, whereas the warming increased the downward heat flux by 5.5%-12.3% in the spring. Our observation indicates that the effects of warming on the exchange process of mass and energy between soil and the atmosphere should be further studied in agro-ecosystem regions.  相似文献   

15.
Abstract

Nitrous oxide (N2O) emissions were measured monthly over 1 year in three ecosystems on tropical peatland of Sarawak, Malaysia, using a closed-chamber technique. The three ecosystems investigated were mixed peat swamp forest, sago (Metroxylon sagu) and oil palm (Elaeis guineensis) plantations. The highest annual N2O emissions were observed in the sago ecosystem with a production rate of 3.3 kg N ha?1 year?1, followed by the oil palm ecosystem at 1.2 kg N ha?1 year?1 and the forest ecosystem at 0.7 kg N ha?1 year?1. The N2O emissions ranged from –3.4 to 19.7 µg N m?2 h?1 for the forest ecosystem, from 1.0 to 176.3 µg N m?2 h?1 for the sago ecosystem and from 0.9 to 58.4 µg N m?2 h?1 for the oil palm ecosystem. Multiple regression analysis showed that N2O production in each ecosystem was regulated by different variables. The key factors influencing N2O emissions in the forest ecosystem were the water table and the NH+ 4 concentration at 25–50 cm, soil temperature at 5 cm and nitrate concentration at 0–25 cm in the sago ecosystem, and water-filled pore space, soil temperature at 5 cm and NH+ 4 concentrations at 0–25 cm in the oil palm ecosystem. R2 values for the above regression equations were 0.57, 0.63 and 0.48 for forest, sago and oil palm, respectively. The results suggest that the conversion of tropical peat swamp forest to agricultural crops, which causes substantial changes to the environment and soil properties, will significantly affect the exchange of N2O between the tropical peatland and the atmosphere. Thus, the estimation of net N2O production from tropical peatland for the global N2O budget should take into consideration ecosystem type.  相似文献   

16.
Feedbacks to global warming may cause terrestrial ecosystems to add to anthropogenic CO2 emissions, thus exacerbating climate change. The contribution that soil respiration makes to these terrestrial emissions, particularly from carbon-rich soils such as peatlands, is of significant importance and its response to changing climatic conditions is of considerable debate. We collected intact soil cores from an upland blanket bog situated within the northern Pennines, England, UK and investigated the individual and interactive effects of three primary controls on soil organic matter decomposition: (i) temperature (5, 10 and 15 °C); (ii) moisture (50 and 100% field capacity – FC); and (iii) substrate quality, using increasing depth from the surface (0–10, 10–20 and 20–30 cm) as an analogue for increased recalcitrance of soil organic material. Statistical analysis of the results showed that temperature, moisture and substrate quality all significantly affected rates of peat decomposition. Q10 values indicated that the temperature sensitivity of older/more recalcitrant soil organic matter significantly increased (relative to more labile peat) under reduced soil moisture (50% FC) conditions, but not under 100% FC, suggesting that soil microorganisms decomposing the more recalcitrant soil material preferred more aerated conditions. Radiocarbon analyses revealed that soil decomposers were able to respire older, more recalcitrant soil organic matter and that the source of the material (deduced from the δ13C analyses) subject to decomposition, changed depending on depth in the peat profile.  相似文献   

17.

Purpose

Alpine ecosystems on the Qinghai-Tibetan Plateau are sensitive to global climatic changes. However, the effects of temperature change resulting from global warming or seasonal variation on soil N availability in those ecosystems are largely unknown.

Materials and methods

We therefore conducted a 15N tracing study to investigate the effects of various temperatures (5–35 °C) on soil gross N transformation rates in an alpine meadow (AM) soil on the Qinghai-Tibetan Plateau. A natural secondary coniferous forest (CF) soil from the subtropical region was chosen as a reference to compare the temperature sensitivity of soil gross N transformation rates between alpine meadow and coniferous forest.

Results and discussion

Our results showed that increasing temperature increased gross N mineralization and NH4 + immobilization rates and overall enhanced N availability for plants in both soils. However, both rates in the CF soil were less sensitive to a temperature change from 5 to 15 °C compared to the AM soil. In both soils, different N retention mechanisms could have been operating with respect to changing temperatures in the different climatic regions. In the CF soil, the absence of NO3 ? production at all incubation temperatures suggests that in the subtropical soil which is characterized by high rainfall, an increase in N availability due to increasing temperature could be completely retained in soils. In contrast, the AM soil may be vulnerable to N losses with respect to temperature changes, in particular at 35 °C, in which higher nitrification rates were coupled with lower NH4 + and NO3 ? immobilization rates.

Conclusions

Our results suggest that increased soil temperature arising from global warming and seasonal variations will most likely enhance soil N availability for plants and probably increase the risk of N losses in the alpine meadow on the Qinghai-Tibetan Plateau.
  相似文献   

18.
ABSTRACT

Antecedent soil moisture before freezing can affect greenhouse gases (GHG) fluxes from soils during thaw, but their critical threshold values for GHG fluxes and the underlying mechanisms are still not clear. By using packed soil-core incubation experiments, we have studied nitrous oxide (N2O), carbon dioxide (CO2) and methane (CH4) fluxes from a mature broadleaf and Korean pine-mixed forest soil and an adjacent white birch forest soil with nine levels of soil moisture ranging from 10 to 90% water-filled pore space (WFPS) during a 2-month freezing at ?8°C and the following 10-day thaw at 10°C. The threshold values of soil moisture ranged from 50 to 70% WFPS for CH4 uptake and from 70 to 90% WFPS for N2O and CO2 emissions from the two soils during the freeze-thaw period. Under the optimum soil moisture condition, fulvic-like compounds with high bioavailability contributed more than 60% of dissolved organic matter (DOM) in the soil. Cumulative N2O emissions from forest soils during the freeze-thaw period were greatest when the concentration ratio of nitrate-N to dissolved organic carbon (DOC) was 0.04 g N g?1 C. Cumulative soil CO2 emissions and CH4 uptake during the freeze-thaw period were both regulated by the interaction between soil DOC and net N mineralization. The activities of β-1,4-glucosidase and β-1,4-N-acetyl-glucosaminidase, microbial biomass C and N, and the microbial biomass C-to-N ratios, were all significantly correlated to the soil N2O, CO2, and CH4 fluxes. Overall, upon a freeze-thaw period with different soil moistures, GHG fluxes from forest soils were jointly regulated by inorganic N and DOC concentrations, and related to the labile components of DOM released into the soil, which could be strictly controlled by the related microbial properties.  相似文献   

19.
Laboratory columns (80 cm long, 10 cm diameter) of peat were constructed from samples collected from a subarctic fen, a temperate bog and a temperate swamp. Temperature and water table position were manipulated to establish their influence on emissions of CO2 and CH4 from the columns. A factorial design experiment revealed significant (P < 0.05) differences in emission of these gases related to peat type, temperature and water table position, as well as an interaction between temperature and water table. Emissions of CO2 and CH4 at 23°C were an average of 2.4 and 6.6 times larger, respectively, than those at 10°C. Compared to emissions when the columns were saturated, water table at a depth of 40 cm increased CO2 fluxes by an average of 4.3 times and decreased CH4 emissions by an average of 5.0 times. There were significant temporal variations in gas emissions during the 6-week experiment, presumably related to variations in microbial populations and substrate availability. Using columns with static water table depths of 0, 10, 20, 40 and 60 cm, CO2 emissions showed a positive, linear relation with depth, whereas CH4 emissions revealed a negative, logarithmic relation with depth. Lowering and then raising the water table from the peat surface to a depth of 50 cm revealed weak evidence of hysteresis in CO2 emissions between the falling and rising water table limbs. Hysteresis (falling > rising limb) was very pronounced for CH4 emissions, attributed to a release of CH4 stored in porewater and a lag in the development of anaerobic conditions and methanogenesis on the rising limb. Decreases in atmospheric pressure were correlated with abnormally large emissions of CO2 and CH4 on the falling limb. Peat slurries incubated in flasks revealed few differences between the three peat types in the rates of CO2 production under aerobic and anaerobic conditions. There were, however, major differences between peat types in the rates of CH4 consumption under aerobic incubation conditions and CH4 production under anaerobic conditions (bog > fen > swamp), which explain the differences in response of the peat types in the column experiment.  相似文献   

20.
Calluna-derived, amorphous H-horizon material from a peaty ferric stagnopodzol was incubated at two constant temperatures: 6° and 20°C and at two fluctuating temperatures: alternating days at 6° and 20°C and at field fluctuating temperatures. After 3 weeks, amounts of mobilized N, P and K at 6°, 20°C and field temperatures were higher than before incubation. Incubated peat at temperatures of 6° and 20°C on alternating days for 3 weeks produced smaller amounts of deionized-distilled water-extractable NH4+-N, P and K than before incubation. For N, P and K, incubation at constant high temperature (20°C) produced similar amounts of mobilized nutrients compared to field surface soil temperatures.The magnitude of deionized-distilled water-extractable N and P in experimental treatments followed a similar sequence: 6°C incubation > field temperatures > 20°C incubation > before incubation > imposed fluctuating 6° and 20°C temperatures. For K, the mobilization sequence was slightly different: 6° incubation > 20°C incubation > field temperatures > before incubation > imposed fluctuation 6° and 20°C temperatures.  相似文献   

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