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1.
Investigations on soil and freshwater acidification are usually focused on well-aerated systems. This study deals with the role of reductive processes for the neutralization of acid soil solution within helocrene springs. Two toposequences consisting each of three profiles (forest soil, margin of fen, fen) were established to study the chemistry of the solid phase (soil pH, CEC, pedogenic Fe- and Al-oxides) and the soil solution in two small spring catchments on three dates during 1991 and 1992. Despite high acid inputs and acidified forest soils the pH of the spring outflow is near neutral, and the soil solid phases of the spring fens are not acidified. The results support the following hypothesis: Aluminum with its corresponding anion sulfate is leached with the soil solution into the water-saturated fens. Dissimilatory iron and sulfate reduction take place within the fen and generate alkalinity. Reduced iron either reacts with sulfide to form pyrite or migrates within the fen profile and precipitates in the uppermost, oxic horizons, consuming part of the generated alkalinity. Due to the higher pH values in the fens the incoming aluminum precipitates releasing acidity. The alkalinity generated exceeds the amount of acidity released by oxidation and precipitation of iron and the precipitation of aluminum. A balance of alkalinity consuming and alkalinity generating processes based on solid phases showed that iron and sulfate reduction can account for at least 67% of the neutralization of acidity entering the fen of one of the catchments. Due to shorter water retention times and higher discharge these processes are of minor importance in the other catchment.  相似文献   

2.
Field and lab-based methane (CH4) fluxes and methanogen community structure were characterized across three peatlands in central Ontario (Canada) representing a successional and nutrient gradient from rich to poor fens. Air temperature was a strong and significant predictor of both CH4 and carbon dioxide (CO2) fluxes among the three sites. Net CH4 efflux and in vitro CH4 production potential were significantly greater in the rich and intermediate than the poor fen site. Although the poor fen site had the lowest water table position, this was not a significant predictor of CH4 emissions and in general the 3 sites were relatively wet compared to many northern peatlands. Consistently, during spring and fall, ethanol stimulated in vitro CH4 production potential from the poor fen, but not the rich and intermediate sites, indicating substrate limitation for CH4 production in the poor fen. Lower rates of CH4 production and emissions in the poor fen site were consistent with our hypotheses based on poorer substrate quality and a lack of sedges in that peatland type. However phylogeny of dominant methanogens inferred from terminal restriction fragment length polymorphism (T-RFLP) analyses of 16S rDNA illustrated inconsistencies with previous reports of methanogens in northern peatlands. For example members likely of the family Methanosaetaceae (obligate high-affinity acetate fermenters) comprised a substantial portion of total methanogen population in the poor fen. In contrast, members of the order Methanomicrobiales (obligate CO2 reducers) were important methanogens in the rich and intermediate fens and not detected in the poor fen. Methanogen community structure based on T-RFLP across the 3 sites was distinct during spring, while during fall methanogen communities in the poor fen samples were still somewhat distinct from those in the rich and intermediate fens. Methanogen diversity (community richness and evenness) was not correlated with rates of CH4 production in the spring when soil respiration, and presumably rhizosphere activity, was slow. However, diversity was a significant predictor of CH4 production in the early fall (when both production and emissions rates were higher), indicating that methanogen diversity can potentially play a role in biogeochemical cycling and greenhouse gas emissions in northern peatlands.  相似文献   

3.
Rice is the staple food crop for about 50% of the world's population. It is grown mainly under two ecosystems, known as upland and lowland. Lowland rice contributes about 76% of the global rice production. The anaerobic soil environment created by flood irrigation of lowland rice brings several chemical changes in the rice rhizosphere that may influence growth and development and consequently yield. The main changes that occur in flooded or waterlogged rice soils are decreases in oxidation–reduction or redox potential and increases in iron (Fe2+) and manganese (Mn2+) concentrations because of the reductions of Fe3+ to Fe2+ and Mn4+ to Mn2+. The pH of acidic soils increased and alkaline soils decreased because of flooding. Other results are the reduction of nitrate (NO3 ?) and nitrogen dioxide (NO2 ?) to dinitrogen (N2) and nitrous oxide (N2O); reduction of sulfate (SO4 2?) to sulfide (S2?); reduction of carbon dioxide (CO2) to methane (CH4); improvement in the concentration and availability of phosphorus (P), calcium (Ca), magnesium (Mg), Fe, Mn, molybdenum (Mo), and silicon (Si); and decrease in concentration and availability of zinc (Zn), copper (Cu), and sulfur (S). Uptake of nitrogen (N) may increase if properly managed or applied in the reduced soil layer. The chemical changes occur because of physical reactions between the soil and water and also because of biological activities of anaerobic microorganisms. The magnitude of these chemical changes is determined by soil type, soil organic-matter content, soil fertility, cultivars, and microbial activities. The exclusion of oxygen (O2) from the flooded soils is accompanied by an increase of other gases (CO2, CH4, and H2), produced largely through processes of microbial respiration. The knowledge of the chemistry of lowland rice soils is important for fertility management and maximizing rice yield. This review discusses physical, biological, and chemical changes in flooded or lowland rice soils.  相似文献   

4.
The availability of O2 is one of the most important factors controlling the chemical and biological reactions in soils. In this study, the effects of different aeration conditions on the dynamics of the emission of trace gases (CO2, N2O, CH4) and the leachate composition (NO3‐, DOC, Mn, Fe) were determined. The experiment was conducted with naturally structured soil columns (silty clay, Vertisol) from a well aerated forest site. The soil monoliths were incubated in a microcosm system at different O2 concentrations (0, 0.001, 0.005, 0.01, 0.05, and 0.205 m3 m‐3 in the air flow through the headspace of the microcosms) for 85 days. Reduced O2 availability resulted in a decreased CO2 release but in increased N2O emission rates. The greatest cumulative N2O emissions (= 1.6 g N2O‐N m‐2) were observed at intermediate O2 concentrations (0.005 and 0.01 m3 m‐3) when both nitrification and denitrification occurred simultaneously in the soil. Cumulative N2O emissions were smallest (= 0.05 g N2O‐N m‐2) for the aeration with ambient air (O2 concentration: 0.205 m3 m‐3), although nitrate availability was greatest in this treatment. The emission of CH4 and leaching of Mn and Fe were restricted to the soil columns incubated under completely anoxic conditions. The sequence of the reduction processes under completely anoxic conditions complied with the thermodynamic theory: soil nitrate was reduced first, followed by the reduction of Mn(IV) and Fe(III) and finally CO2 was reduced to CH4. The re‐aeration of the soil columns after 85 days of anoxic incubation terminated the production of CH4 and dissolved Fe and Mn in the soil but strongly increased the emission rates of CO2 and N2O and the leaching of NO3‐ probably because of the accumulation of DOC and NH4+ during the previous anoxic period.  相似文献   

5.
Floodplain soils are characterized by frequent and extreme redox changes caused by inundation with river water or imbibition of groundwater. Depending on the duration and extent of inundation, biogeochemical processes run at sub‐/anoxic conditions, which may result in the mobilization and relocation of dissolved and particulate matter within the soil. In this study, we investigated the effect of inundation events on the composition of mobilized matter in the topsoil horizon of a floodplain soil. We conducted experiments with soil columns in the laboratory and gravitational lysimeters in the field to identify redox‐mediated (im)mobilization processes and to estimate their relevance under field conditions. The lysimeters were filled with topsoil monoliths and run under in situ conditions during a ≈ 2.5‐y period. The soil columns were run with the same soil material either under strictly anoxic or mixed oxic–anoxic conditions. Effluents from mixed oxic–anoxic soil were composed fundamentally different [comparably high: Mn, Al, nitrate, sulfate; comparably low: pH, organic C (OC); not detected: Fe, As] compared to effluents from strictly anoxic soil (comparably high: pH, Fe, Mn, OC, As; comparably low: Al; not detected: nitrate, sulfate). Matter, which was mobile under anoxic conditions (e.g., Fe, As, OC), was effectively immobilized as soon as the mobile phase passed anoxic–oxic boundaries within soil (exception: Mn). We assume that the solution in the soil monoliths always passed such anoxic–oxic boundaries during downwards migration independent of lysimeter flooding with river water. This is indicated by the similar composition of the lysimeter seepage water and the effluents from mixed oxic–anoxic soil columns. Both solutions contained “fingerprints” from anoxic (Mn) and oxic conditions (nitrate). Inundations with river water and the duration of these floods (1–22 d) did not affect the composition of the lysimeter seepage water. In conclusion, immediate changes in the composition of the solution, which enters either the subsoil or nearby receiving waters, cannot be expected from regular topsoil flooding.  相似文献   

6.
The impact of climate change on the greenhouse gas balance of peatlands is debated as they function both as sinks of carbon and significant sources of methane. To study redox transformations influencing methane production, we incubated two intact soil monoliths from a northern temperate fen and compared a permanently wet treatment to a treatment undergoing an experimentally induced drought for 50 days. Net turnover of dissolved inorganic carbon (DIC), methane (CH4) and electron acceptors in the saturated zone was calculated using a mass balance approach, and sulfate gross reduction rates were determined using a 35S radiotracer. Thermodynamic energy yield of different electron accepting processes was calculated and related to the observed respiration patterns. Permanently wet conditions lead to a depletion of electron acceptors within 50 days and onset of methanogenic conditions. During drought, electron acceptors were renewed and methanogenesis was temporarily suppressed in most of the peat for another 20-50 days after rewetting. Methanogenesis began, however, apparently locally before electron acceptors were fully depleted in the remainder of the peat, and iron and sulfate reduction occurred simultaneously. Anaerobic production of DIC could mostly but not fully be explained by reduction of nitrate, sulfate and ferric iron. Sulfate gross reduction rates of up to ∼450 nmol cm−3 d−1 determined with 35S-SO4 and potentially explained the surplus of 50-60 mmol m−2 of DIC production in one treatment; however, the sulfate pools were too small to sustain such rates beyond some hours to days. Furthermore, anaerobic DIC production proceeded at constant rates after depletion of dissolved inorganic electron acceptors, although not being balanced by methane production. An unknown electron acceptor was thus consumed, and sulfate and potentially other electron acceptors recycled, either by humic substances, by aerenchymatic oxygen transport, or by oxygen in the capillary fringe at low levels of air filled porosity.  相似文献   

7.
Abstract

The relationships between methane (CH4) emission from flooded rice paddies and soil chemical properties were investigated using eight different soils in a pot experiment. Since CH4 is produced in paddy soil microbiologically when reducing conditions are sufficiently developed, the amounts of oxidizing agents including free iron (Fe)(III), amorphous Fe(III), easily reducible manganese (Mn), nitrate (NO3 ‐), and sulfate (SO4 2‐), and indexes of reducing agents including total carbon (C), total nitrogen (N), and easily decomposable C, were measured as possible decreasing and increasing factors in CH4 emission. The seasonal variations in CH4 emission rates were similar in pattern among the soils used. However, the amount of emitted CH4 varied largely, with the maximum total CH4 emission (from a brown lowland soil, 1,535 mg pot‐1) being 3.8 times that of the minimum (from a gley soil, 409 mg pot‐1). No correlation was found between the total CH4 emission and any single factor investigated. However, a statistically significant equation was found through multiple regression analysis: r=‐2.24x102 a+2.88b+6.20x102; r 2=0.821; P<0.01; where Y is the amount of emitted CH4 (mg pot‐1), a is the amount of amorphous Fe(III) (mg pot‐1), b is the amount of easily decomposable C (mg pot‐1), and r 2 is a multiple correlation coefficient adjusted for the degree of freedom. The amendment of ferric hydroxide [Fe(OH)3] to a gray lowland soil significantly decreased the CH4 emission from 1,099 to 592 mg pot‐1. This measured amount agreed well with that estimated from the above equation, 554 mg pot‐1.  相似文献   

8.
土壤中铁的氧还过程与碳氮转化及自净能力关系密切,已还原亚铁的氧化受土壤性质的影响。采用室内恒温培养试验研究了旱作褐土中铁还原氧化过程、及其与水溶性碳、NO3-、SO42-的关系。结果表明旱作褐土中铁氧化物在厌氧光照条件下可先被还原后被再次氧化,其再氧化量介于1.46~3.00 mg g-1之间,平均2.09 mg g-1;再氧化速率常数介于0.23~0.80 d-1之间,平均0.48 d-1。再氧化量与土壤无定形铁、水溶性硫酸盐含量、阳离子交换量显著负相关,与土壤总氮、总磷显著正相关;再氧化速率常数与土壤有机碳显著负相关,与黏粒含量极显著正相关。厌氧光照培养可使旱作褐土水溶性无机碳平均降低52.74%,水溶性NO3-降低92.15%,水溶性SO42-增加55.38%。研究结果为深入理解旱作土壤潜在的微生物铁循环转化方式提供理论支持。  相似文献   

9.
Estimating future fluxes of CH4 between land and atmosphere requires well-conceived process-based biogeochemical models. Current models do not represent the anaerobic oxidation of methane (AOM) in land surface soils, in spite of increasing evidence that this process is widespread. Our objective was to determine whether AOM, or potential AOM, commonly occurs in 20 hydromorphic soils spanning a wide range of chemical properties. Bulk soil samples were collected under shallow water near the shoreline of 15 recently drained fish ponds in southern Bohemia (Czech Republic), as well as from below the water table at 3 peatland locations in northeast Scotland and 2 acid sulfate soils on the southern coast of Finland. Each soil slurry was incubated under both oxic and anoxic conditions, with or without the addition of alternative electron acceptors (SO42− and NO3−) or H2PO4−. Here, “oxic” and “anoxic” conditions refer to anoxic soil respectively incubated in a headspace containing air or argon. Using the isotope dilution method, we determined the gross production and oxidation rates of CH4 after 2 days incubation under oxic headspace conditions, and after 2, 21 and 60 days incubation under anoxic conditions. Large differences in net CH4 fluxes were observed between soil types and between incubation conditions. AOM was detected in each of the 20 bulk soil samples, which spanned >6 pH units and 2 orders of magnitude in organic C content. Significant positive relationships were found between AOM and gross CH4 production rates under anoxic conditions, resulting in AOM rates that were sometimes higher than CH4 oxidation rates under oxic headspace conditions. There was no relationship between net and gross CH4 production rates, such that 2 soil types could display similar low net rates, yet conceal very large differences in gross rates. The effects of alternative electron acceptors on AOM were idiosyncratic and resulted in no net trend. We did find, however, a negative effect of SO42− and H2PO4− on gross CH4 production rates under anoxic and oxic conditions respectively. Under oxic headspace conditions, CH4 oxidation was related to soil organic C content. Taken collectively, our results suggest that AOM, or potential AOM, is prevalent over a wide range of soil types, that AOM may contribute substantially to CH4 oxidation in soils, and that AOM in soils should be integrated to current process-based CH4 cycling models.  相似文献   

10.
 At two field sites representing northeastern German minerotrophic fens (Rhin-Havelluch, a shallow peat site; Gumnitz, a partially drained peat site) the influence of different factors (N fertilization, groundwater table, temperature) on N2O and CH4 emissions was investigated. The degraded fens were sources or sinks of the radiatively active trace gases investigated. The gas fluxes measured were much higher than those found in other terrestrical ecosystems such as forests. Lowering the groundwater table increased the release of N2O and the oxidation of CH4. High CH4 emission rates occurred when the groundwater tables and soil temperatures were high (>12  °C). N fertilization stimulated the release of N2O only when application rates were very high (480 kg N ha–1). A moderate N supply (60 or 120 kg N ha–1) hardly increased the release of N2O in spite of high soluble soil NO3 – contents. Received: 31 October 1997  相似文献   

11.
Summary Reduction processes in cultivated soil during the decomposition of liquid cattle manure were studied in laboratory experiments. Anoxic slurries of soil and manure in different proportions or alone were followed over 5 weeks. Upon NO inf3 sup- depletion, ferrous Fe appeared in solution in soil-manure slurries. Sulfide levels were generally low in the presence of both soil and manure, probably because of precipitation by Fe2+; Fe thereby counteracted the production of free hydrogen sulfide. Methane formation was the quantitatively most important electron sink under prolonged anoxic conditions. When extra sulfate was added to soil-manure slurries, the concentration of Fe2+ remained low and less methane was produced. The detection of Fe2+ was examined in a model system with a gel-stabilized soil-manure mixture sandwiched between two soil phases with a water content near field capacity. Large methodological problems made it impossible to quantify Fe2+ in this oxic-anoxic environment, but the results indicated that reducing conditions were maintained in the manure-saturated zone for the 20-day period of this experiment.  相似文献   

12.
Peatlands, including fens, are important ecosystems in the context of the global carbon cycle. Future climate change and other anthropogenic activities are likely to increase nutrient loading in many peatland ecosystems and a better understanding of the effects of these nutrients on peatland carbon cycling is necessary. We investigated the effects of six years of nitrogen and phosphorus fertilization, along with liming, on carbon mineralization dynamics in an intermediate fen in northern Minnesota. Specifically, we measured CO2 and CH4 emission from intact peat cores, as well as CH4 production and CH4 consumption at multiple depths in short-term laboratory incubations. Despite increased nitrogen and phosphorus availability in the upper 5 cm of peat, increased pH, and clear shifts in the vegetation community, fertilization and liming had limited effects on microbial carbon cycling in this fen. Liming reduced the net flux of CO2 approximately 3-fold compared to the control treatment, but liming had no effect on CH4 emissions from intact cores. There were no nutrient effects on CO2 or CH4 emissions from intact cores. In all treatments, rates of CH4 production increased with depth and rates of CH4 consumption were highest near the in situ water-table level. However, nutrient and liming had no effect on rates of CH4 production or CH4 consumption at any depth. Our results suggest that over at least the intermediate term, the microbial communities responsible for soil carbon cycling in this peatland are tolerant to wide ranges of nutrient concentrations and pH levels and may be relatively insensitive to future anthropogenic nutrient stress.  相似文献   

13.
Abstract

The effects of nitrogen (N) and sulfur (S) deposition on methane (CH4) and nitrous oxide (N2O) emissions under low (10 cm below soil surface) and high (at soil surface) water tables were investigated in the laboratory. Undisturbed soil columns from the alpine peatland of the Tibetan Plateau were analyzed. CH4 emission was higher and N2O emission was lower at the high water table than those at the low water table regardless of nutrient application. Addition of N (NH4NO3 (ammonium nitrate), 5 g N m?2) decreased CH4 emission up to 57% and 50% at low and high water tables, respectively, but correspondingly increased N2O emission by 2.5 and 10.4 times. Addition of S (Na2SO4 (sodium sulfate), 2.5 g S m?2) decreased CH4 and N2O emission by 64% and 79% at the low water table, respectively, but had a slightly positive effect at the high water table. These results indicated that the responses of CH4 and N2O emissions to the S deposition depend on the water table condition in the high-altitude peatland.  相似文献   

14.
Abstract

The changes in availability and uptake of boron (B) by M.26 apple rootstocks as affected by applications of different forms and rates of nitrogen (N) were examined. The study was carried out in a greenhouse using soil with low contents of organic matter, clay, calcium carbonate, NH4‐oxalate soluble aluminum (Al) and iron (Fe), NH2OH·HCl extractable manganese (Mn), poor cation exchange capacity and low pH. Soil N application was in the form of urea, calcium nitrate, ammonium sulphate, or ammonium nitrate at rates of 0, 17, 34, and 51 mg N kg?1. After 1, 3, and 5 days of N application, soil B fractions were determined: B in soil solution, B specifically and non‐specifically adsorbed on soil surfaces, B occluded in Mn oxyhydroxides, and B occluded in crystalline Al and Fe oxides. The results showed that N as calcium nitrate and ammonium nitrate increased B both in soil solution and non‐specifically adsorbed on soil surface and decreased B concentration on Al and Fe oxides. This indicates that N‐NO3 inhibited B sorption on Fe and Al oxides. Maximum B desorption from Fe and Al oxides was obtained within one day after N‐NO3 was supplied. Nitrogen application as calcium nitrate and ammonium nitrate increased availability and uptake of B by plant roots. Thus, it was concluded that apple trees planted on coarse‐textured soils where risk of B deficiency is high, calcium nitrate or ammonium nitrates would be appropriately to apply to keep B more available.  相似文献   

15.
Boreal wetlands are characterized by a mosaic of plant communities, including forests, shrublands, grasslands, and fens, which are structured largely by changes in topography and water table position. The soil associated with these plant communities contain quantitatively and qualitatively different forms of soil organic matter (SOM) and nutrient availability that drive changes in biogeochemical cycling rates. Therefore different boreal plant communities likely contain different soil biotic communities which in turn affect rates of organic matter decomposition. We examined relationships between plant communities, microbial communities, enchytraeids, and soil C turnover in near-surface soils along a shallow topographic soil moisture and vegetation gradient in interior Alaska. We tested the hypothesis that as soil moisture increases along the gradient, surface soils would become increasingly dominated by bacteria and mesofauna and have more rapid rates of C turnover. We utilized bomb radiocarbon techniques to infer rates of C turnover and the 13C isotopic composition of SOM and respired CO2 to infer the degree of soil humification. Soil phenol oxidase and peroxidase enzyme activities were generally higher in the rich fen compared with the forest and bog birch sites. Results indicated greater C fluxes and more rapid C turnover in the surface soils of the fen sites compared to the wetland forest and shrub sites. Quantitative PCR analyses of soil bacteria and archaea, combined with enchytraeid counts, indicated that surface soils from the lowland fen ecosystems had higher abundances of these microbial and mesofaunal groups. Fungal abundance was highly variable and not significantly different among sites. Microbial data was utilized in a food web model that confirmed that rapidly cycling systems are dominated by bacterial activity and enchytraeid grazing. However, our results also suggest that oxidative enzymes play an important role in the C mineralization process in saturated systems, which has been often ignored.  相似文献   

16.
 Wetland rice soils from Italy (Pavia) and the Philippines (Bugallon, Luisiana, Maligaya) were incubated under anoxic conditions at 31 different temperatures ranging from 4.7  °C to 49.5  °C. Production of CO2 was most intensive at the beginning of the incubation (0–4 days) and was predominantly coupled to the reduction of free Fe(III). The optimum temperature for these processes was between 32  °C and 41  °C. After 9–16 days, CO2 production rates had decreased and the available Fe(III) had been completely reduced at the optimum temperatures. However, Fe(III) was still available at temperatures below and above the optimum. Maximum CH4 production rates were observed after 4–16 days (except in soil from Maligaya) with temperature optima between 32  °C and 41  °C, similar to those for CO2 production and Fe reduction. Since ongoing Fe reduction is known to suppress CH4 production, the temperature range of optimum CH4 production was restricted to those temperatures at which Fe(III) had already been depleted. Nevertheless, the temperature characteristics of both CO2 and CH4 production often exhibited two temperature optima at some time during the incubation, suggesting a complex pattern of adaptation of the methanogenic microbial community to temperature. When available Fe(III) was completely depleted by anoxic pre-incubation at 30  °C, CH4 was produced at a constant rate (steady state conditions) which increased with increasing temperature. Steady state CH4 production reached a first maximum at about 40  °C, but increased further up to at least 50  °C, suggesting the presence of thermophilic microorganisms whose activity was apparently masked when Fe had not been completely reduced. The apparent activation energy of CH4 production at steady state ranged between 48 kJ mol–1 and 65 kJ mol–1. Received: 26 August 1999  相似文献   

17.
Abstract

When a soil is flooded, iron (Fe) reduction and methane (CH4) production occurred in sequence as predicted by thermodynamics. The dissolution and precipitation of Fe reflected both soil pH and soil redox potential (Eh). The objective of our experiment was to determine both CH4 production and Fe reduction as measured by Fe in solution in a flooded paddy soil over a wide range of closely controlled pH and Eh conditions. The greatest release of CH4 gas occurred at neutral soil pH in combination with low soil redox potential (‐250 mV). Production of CH4 decreased when soil pH was lowered in combination with an increase in the soil redox potential above ‐250 mV. Highest concentration of ferrous‐iron (Fe2+) under reducing conditions occurred when soil pH was lowered. Thus Fe reduction influenced CH4 formation in the flooded paddy soil. Results indicated that CH4 production was inhibited by the process of ferric‐iron (Fe3+) reduction.  相似文献   

18.
The microbial activity and bacterial community structure were investigated in two types of peat soil in a temperate marsh. The first, a drained grassland fen soil, has a neutral pH with partially degraded peat in the upper oxic soil horizons (16% soil organic carbon). The second, a bog soil, was sampled in a swampy forest and has a very high soil organic carbon content (45%), a low pH (4.5), and has occasional anoxic conditions in the upper soil horizons due to the high water table level. The microbial activity in the two soils was measured as the basal and substrate-induced respiration (SIR). Unexpectedly, the SIR (μl CO2 g−1 dry soil) was higher in the bog than in the fen soil, but lower when CO2 production was expressed per volume of soil. This may be explained by the notable difference in the bulk densities of the two soils. The bacterial communities were assessed by terminal restriction fragment length polymorphism (T-RFLP) profiling of 16S rRNA genes and indicated differences between the two soils. The differences were determined by the soil characteristics rather than the season in which the soil was sampled. The 16S rRNA gene libraries, constructed from the two soils, revealed high proportions of sequences assigned to the Acidobacteria phylum. Each library contained a distinct set of phylogenetic subgroups of this important group of bacteria.  相似文献   

19.
《Soil biology & biochemistry》2001,33(12-13):1613-1623
Methane is an important greenhouse gas and CH4 oxidation in soil represents a significant sink for this gas. High capacity CH4 oxidation potentials and molecular profiles of CH4 oxidizing bacteria in soil were compared for five land-use treatments at a fully replicated experimental site within the Gisburn Forest Experiment, to assess the effects of land-use on both the potential activity of CH4 oxidizing bacteria and their diversity. Forestry land-use was found to have a highly significant effect on CH4 oxidation potentials. Highest CH4 oxidation potentials were found in soils collected under stands of oak, in grassland plots, and in one soil under Norway spruce. A negative relationship between soil water nitrate concentration and CH4 oxidation capacity was evident across the experimental site, with the high nitrate soils under stands of alder exhibiting little or no capacity for CH4 oxidation even at optimal temperature and water content. Molecular profiles indicated that a diverse range of bacteria with the potential to oxidize CH4 were present in all soils, however no clear correlation with CH4 oxidation potential was identified.  相似文献   

20.
Abstract

Upland pastures on coarse‐textured sulphur (S)‐deficient soils in moderate to high rainfall areas may benefit from S fertilization using elemental S to avoid leaching losses. Two grades of elemental S, 120 and 300 mesh, were assessed as a source of S for grass and clover. In laboratory incubations using an upland soil at 7 and 14°C, oxidation of the 120 mesh S was very slow while 65% of the 300 mesh S was oxidized after 48 days at 14°C. In pot trials of ryegrass in a lowland soil and of ryegrass and clover in the upland soil both elemental S grades gave satisfactory yield increases which were not significantly different from applying potassium sulphate. High ambient temperatures during the pot experiment probably ensured an adequate oxidation rate of both elemental S grades. High application rates of the potassium sulphate gave rise to luxury consumption while very high rates of elemental S (equivalent to 200 kg S ha‐1) showed some toxicity. Application of a previously‐described model of S oxidation confirmed the importance of soil temperature in controlling S oxidation rates.  相似文献   

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