首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 78 毫秒
1.
Detached lenticellate warty bark of Inga laurina was first shown to develop acetylene reducing activity (ARA) (18 nmol C2H2red·g-1 (F.W.)·hr-1) after a few days' incubation with ambient air containing 0.10 atm C2H2. Similar N2ase development was found to occur with warty barks of many other plant species including 12 leguminous and 9 non-leguminous trees growing in wet tropical and temperate forests. Among them higher activities (>7 nmol C2H2 red·g-1 (F.W.)·hr-1) were recorded in Inga laurina, Cynometra ramiflora, Cassia siamea, Robinia pseudo-acacia, Albizia julibrissin in the leguminous plants, and Ilex crenata, Ilex pedunculosa, Rhizophora mucronata, Bruguiera gymnorrhiza and Mallotus japonicus in the non-leguminous plants. The development of ARA was often accelerated under lower pO2 (0.05 atm) and pC2H2 (0.05 atm). Complete replacement of O2 with N2 or Ar in the incubation atmosphere resulted in full suppression of the development of N2ase activity.

When ARA measurement was made with intact barks of natural stands (Robinia pseudo-acacia, Ilex pedunculosa and Mallotus japonicus), it was found that all of these intact barks were reducing C2H2 linearly without any time lag. The activities recorded were 4.6–11.5 nmol C2H2 red·g-1 (F.W.)·hr-1 corresponding to 1.19–1.27 nmol C2H2 red·cm-2hr-1. These values roughly coincided with ARA of detached warty barks of the same plant species. The present results suggest that in situ N2-fixation in tree barks of the forests would amount to several 10 kg·ha-1·year-1 in temperate and tropical wet forests  相似文献   

2.
Nitrogen fixation and acetylene reduction activities were studied in a sandy loam soil amended with glucose (2% w/w) at field moisture content and incubated anaerobically. Optimum temperature for C2H2 reduction was about 37°C and the maximum was 45°C. Q10 values were 1.6–3.7 in the range 10–35°C. Calculated activation energies were lower than those reported for Clostridium whole cells. Apparent Km (C2H2) averaged 0.006 atm pC2H2 and the apparent Km (N2) was 0.095 atm pN2. Low concentrations of C2H2 competed strongly with N2 for the soil N2ase (apparent K[ini] was 0.0003 atm pC2H2 with 0.8 atm pN2). A relatively high concentration of ethylene (0.22 atm pC2H4) caused 30–40 per cent inhibition of N2ase activity (measured as 15N2 fixation) but the lower concentrations likely to be encountered in C2H2 assays had no significant effect. Conversion factors (C2H4/N2 molar ratios) determined under various conditions ranged from 0.75 to 3.6. A value of 2.6 was obtained using the most favourable short-term C2H2 assays.  相似文献   

3.
A study was made on the effects of landfill gas on ARA (acetylene reducing activity) of nodules of two woody legumes (Acacia confusa and Leucaena leucocephala) widespread on landfill sites in Hong Kong. The effects of the three main components of landfill gas, O2, CO2 and CH4, were first measured separately over a 1-hr period. Maximum ARA was found at 20% O2 (close to atmospheric partial pressure) and ARA decreased as the O2 decreased in the range of 16–1%. Acacia confusa nodular ARA was significantly inhibited at 30–50% CO2, but not Leucaena leucocephala nodular ARA. CH4 had no significant effect on ARA of either species. As the landfill gas concentrations in the landfill topsoil were mostly > 10% O2 and < 10% CO2, root nodules should fix N2 effectively over these ranges of gases. A four-week test was conducted to assess the long-term influence of landfill gas on seedlings of the two legumes. Landfill gas and elevated CO2 both suppressed their growth and their nodular ARA. Even under the influence of the gases, however, seedlings with nodules formed a higher biomass than seedlings lacking nodules. The growth of the two legumes under actual landfill conditions was investigated by transplanting non-inoculated and pre-inoculated seedlings to two landfill sites in Hong Kong: Junk Bay and Shuen Wan Landfill. After six months, most of the non-inoculated seedlings became infected: Acacia confusa 63 and 70%, Leucaena leucocephala 17 and 89%, respectively, at the test sites. The results indicate that there were free rhizobia at these landfill sites to infect the legumes and they had formed effective nodules to fix N2 under landfill conditions.  相似文献   

4.
Fifty-seven bacteria were isolated from soil suspensions incubated under pO2 of 1.5 or 159 mm Hg and their growth and generic characteristics were elucidated.The isolates were cultured under both high (159 mm Hg) and low (3 mm Hg) pO2. On the basis of their growth responses to the different pO2, the isolates were classified into two types; (A-type) the lag time, specific growth rate, and/or maximum growth depended on pO2, and (B-type) these three growth characteristics did not depend on pO2. B-types were found only among isolates from soil suspensions incubated under the low pO2. The respiration of some B-type isolates was inhibited by higher pO2. No A-type isolates were inhibited by high pO2.The isolates were classified into eight generic groups: Under 159 mm Hg O2, Groups I(Bacillus spp) and IV(Pseudomonas spp etc.) dominated the others; under 1.5 mm Hg O2, Group I, III(coryneform bacteria) and V(Alcaligenes spp etc.) dominated. Microaerophilic isolates (isolated only from the soil suspension incubated under 1.5 mm Hg O2) were classified into Group V. Isolates belonging to the B-type were classified into the coryneform and Group V bacteria.  相似文献   

5.
In the C2H2-C2H4 assay for measurement of heterotrophic N2 fixation in water-logged soils, the diffusion of C2H2 into the soil and the recovery of C2H4 from it are critical factors regulating the assay result. To establish an C2H2-C2H4 assay technique suitable for waterlogged soils, the C2H2-reducing activities (ARA), assayed by varying the method of assay gas filling, the pC2H2 of the assay gas, the duration of assay incubation and of soil vibration before the gas sampling, were compared.

A maximum ARA was measured when the following set of procedures were applied to the soil sample in assay flasks: 1) a 4-fold repetition of I-min evacuation under 0.01 atmospheric pressure and the subsequent I-min filling under 1 atmospheric pressure with assay gas at pC2H2 of 0.1 atm, 2) an assay incubation for 3 hr, and 3) a sampling of an aliquot of the headspace gas after strongly vibrating the flask for 1 min.

The ARA measured by this technique was several times larger than those measured by the techniques hitherto applied, and corresponded to an almost 80% of the V max of the sample. This technique was, therefore, proposed for the assay of heterotrophic N2 fixation in waterlogged soils.

A striking depression of ARA in the soil sample prepared with agitation indicated that a microbial ecosystem established in the soil should be kept as undisturbed as possible throughout the C2H2-C2H4 assay.  相似文献   

6.
Intact soil cores containing plants of Paspalum notatum or Digitaria decumbens were selected with the acetylene reduction method, and then exposed to 15N15 to confirm nitrogen fixation in tropical grass-bacteria associations. In a preliminary experiment with P. notatum15N2 incorporation was slow but progressive during 24 h in roots but translocation to rhizomes and leaves ceased after 17h. With improved assay chambers, enrichments of 0.151 and 0.563 15N atom % excess were obtained in roots of D. decumbens cv transvala and P. notatum systems respectively, after 3 days. Enrichments in rhizomes were similar to those of roots; however in the leaves only 8% of root enrichment was observed. The addition of sucrose to the soil doubled N2-fixation in roots in both grass species studied, but did not result in increased incorporation into the leaves of P. notatum.  相似文献   

7.
Long range transport of episodic concentrations of O3 into the Appalachian Mountains of Virginia was recorded in the summer season of 1979 and 1980. Continuous monitoring of O3 indicated monthly averages of ? 0.05 ppm O3 and several periods averaged ? 0.08 ppm O3. Open-top chambers were used to test the effect of ambient doses of the pollutant on the growth of 8 planted forest tree species native to the area. Height growth was suppressed for all species at the end of the second growing season when grown in open plots (no chamber) and ambient chambers compared to those grown in charcoal-filtered air supplied chambers. Height growth trends of open < ambient chamber < filtered air chamber were consistent. Virginia pine and green ash were significantly taller (p=0.10) when grown within filtered air chambers. Tulip poplar and green ash manifested purple stippling on the adaxial leaf surface and sweetgum developed purple coloration under open or ambient chamber conditions; other species exhibited no visible injury.  相似文献   

8.
The reliability of the C2H2 reduction test for estimating the activity of N2-fixing bacteria associated with the roots of cereals has been evaluated in Scottish soils. Six wheat cultivars, including two chromosome substitution lines, and five barley cultivars were grown in a glasshouse in nine soils from the North East of Scotland. All the soils exhibited C2H4 oxidase activity which was completely inhibited by 0.0001–0.1 atm C2H2. Over-estimation of C2H2 reduction, resulting from the accumulation of endogenous C2H4, could, therefore, occur in assays of undisturbed plants, with the real possibility of deducing the existence of N2-fixation where none existed. However, radiolabelled C2H2 reduction tests on undisturbed plants producing 2.4–18.0 μmol C2H4 day?1, showed that all the C2H4 had been derived from the C2H2. With less active plants, the source of the C2H4 could not be accurately determined by this tracer method. These low rates of C2H4 production (< 2.4 μmol C2H4 day?1), referred to as apparent C2H2 reduction, should, therefore, not be considered proof of N2-fixation.The highest C2H2 reduction activities were observed in soils at maximum water holding capacity (MWHC). Roots removed from these soils reduced C2H2 immediately, if the initial partial pressure of O2 (pO2) was < 0.1 atm. Roots washed free of soil did not oxidize C2H4 during the 8 h assay. The C2H2 reduction activities of these excised roots could not be related to the activity of plants in soil for three reasons. (1) Development of C2H2 reduction was dependent on protein synthesis (inhibited by chloramphenicol), indicating re-establishment of activity destroyed by exposure to atmospheric pO2, rather than continuation of the activity of undisturbed roots. (2) A lag period, dependent on the volume of the incubation vessel, was observed, indicating the involvement of root respiration in the assay. (3) Growth of N2-fixing bacteria on compounds released from the roots (reducing sugars, amino acids and α-keto acids) occurred during the assay.Even with the possibility of over-estimation of N2-fixation, the C2H2 reduction activities measured were considered to be too low to contribute significantly to the nitrogen requirement of the cereals grown under field conditions in Scotland.Some guidelines for screening programmes of N2-fixation associated with the roots of grasses are suggested.  相似文献   

9.
Summary Wheat seedlings were inoculated with rhizosphere nitrogen-fixing bacteria and grown gnotobiotically for 15 days. The growth medium consisted of semisolid agar with or without plant nutrients. The bacteria, isolated from roots of field-grown wheat, were three unidentified Gram-negative rods (A1, A2, E1), one Enterobacter agglomerans (C1) and two Bacillus polymyxa (B1, B2). A strain of Azospirillum brasilense (USA 10) was included for comparison.Nitrogenase activity (acetylene reduction activity, ARA) was tested on intact plants after 8 and 15 days of growth. In semisolid agar without plant nutrients, five isolates showed ARA of 0.01–0.9 nmol C2H4 plant–1 h–1, while the two strains of B. polymyxa had higher ARA of 3.3–10.6 nmol C2H4 plant–1 h–1.Plant development was not affected by inoculation with bacteria, except that inoculation with B. polymyxa resulted in shorter shoots and lower root weight.Transmission electronmicroscopy of roots revealed different degrees of infection. A. brasilense, A1 and A2, occurred mainly in the mucilage on the root surface and between outer epidermal cells (low infectivity). B. polymyxa strains and E1 were found in and between epidermal cells (intermediate infectivity) while E. agglomerans invaded the cortex and was occasionally found within the stele (high infectivity).  相似文献   

10.
Dissimilatory nitrate reductase in soils is the enzyme that catalyzes the reduction of NO33− to NO2− under anaerobic conditions. The detection of this enzyme in soils is reported, and a simple, sensitive and precise method to assay its activity is described. The method involves determination of the NO2−-N produced when soil. 2,4-dinitrophenol (DNP), and KNO3 are incubated under waterlogged conditions at 25°C for 24 h. At a certain concentration, depending on the soil type, DNP inhibits nitrite reductase but not nitrate reductase. The DNP concentration required for optimum NO2− production in five soils ranged from 5 to 300 μg DNP g−1 soil. The nitrate reductase activity of six soils studied ranged from 18 to 80 μg NO2−-N produced g−1 soil 24 h−1. Optimum activity was found at 5 mM KNO3 and nitrate reductase was inhibited at >5 mM KNO3. Nitrate reductase activity in soils is inactivated at temperatures above 40°C and is completely destroyed by steam sterilization. The relationship between duration of incubation and the amount of NO2−-N produced showed a lag of about 10 h, but in general, thereafter, this relationship was linear for a certain period of incubation, which varied among the soils studied. The duration of the lag was reduced, but not completely eliminated, either by previous incubation for 10 h or by bubbling N2 gas in the soil-water mixture for 3 min to remove the dissolved O2 in the soil-water mixture before addition of NO3−. The relationship between the amount of soil used and the NO2−-N produced was linear unless the substrate concentration was limiting the reaction rate. Application of the Lineweaver-Burk transformation of the Michaelis-Menten equation indicated that the Km values for nitrate reductase in Ames and Okoboji soils were 3.7 and 2.9, respectively, and the Vmax values were 122 and 126μg NO2−-N produced g− soil 24 h−.  相似文献   

11.
Plant response to increasing atmospheric CO2 partial pressure (pCO2) depends on several factors, one of which is mineral nitrogen availability facilitated by the mineralisation of organic N. Gross rates of N mineralisation were examined in grassland soils exposed to ambient (36 Pa) and elevated (60 Pa) atmospheric pCO2 for 7 years in the Swiss Free Air Carbon dioxide Enrichment experiment. It was hypothesized that increased below-ground translocation of photoassimilates at elevated pCO2 would lead to an increase in immobilisation of N due to an excess supply of energy to the roots and rhizosphere. Intact soil cores were sampled from Lolium perenne and Trifolium repens swards in May and September, 2000. The rates of gross N mineralisation (m) and NH4+ consumption (c) were determined using 15N isotopic dilution during a 51-h period of incubation. The rates of N immobilisation were estimated either as the difference between m and the net N mineralisation rate or as the amount of 15N released from the microbial biomass after chloroform fumigation. Soil samples from both swards showed that the rates of gross N mineralisation and NH4+ consumption did not change significantly under elevated pCO2. The lack of a significant effect of elevated pCO2 on organic N turnover was consistent with the similar size of the microbial biomass and similar immobilisation of applied 15N in the microbial N pool under ambient and elevated pCO2. Rates of m and c, and microbial 15N did not differ significantly between the two sward types although a weak (p<0.1) pCO2 by sward interaction occurred. A significantly larger amount of NO3− was recovered at the end of the incubation in soil taken from T. repens swards compared to that from L. perenne swards. Eleven percent of the added 15N were recovered in the roots in the cores sampled under L. perenne, while only 5% were recovered in roots of T. repens. These results demonstrate that roots remained a considerable sink despite the shoots being cut at ground level prior to incubation and suggest that the calculation of N immobilisation from gross and net rates of mineralisation in soils with a high root biomass does not reflect the actual immobilisation of N in the microbial biomass. The results of this study did not support the initial hypothesis and indicate that below-ground turnover of N, as well as N availability, measured in short-term experiments are not strongly affected by long-term exposure to elevated pCO2. It is suggested that differences in plant N demand, rather than major changes in soil N mineralisation/immobilisation, are the long-term driving factors for N dynamics in these grassland systems.  相似文献   

12.
Sandy loam soil was amended with different concentrations of glucose and was incubated at different pO2 levels. Under many conditions of incubation time and treatment, N2 ase activity as determined by 1-h aerobic C2H2 reduction assay (flushed with Ar:O2, 4:1 before assay) was significantly less than that determined by means of ambient assay (carried out at the pO2 of incubation without flushing with Ar:O2, 4:1 before assay). The difference between the N2ase activity in aerobic assay and that in ambient assay increased with decreasing glucose and O2 concentrations imposed during incubation. The inhition in aerobic assays was analogous to O2-induced shut-off of N2ase and amounted to 75 per cent inhibition after incubation at 0.06 atm pO2 of samples amended with 0.75% glucose (w/w). Similar O2 inhibition was observed after amendment with mannitol and with lactate. Times of incubation were chosen such that development of anaerobic N2ase activity was either absent or too low to account for the observed effects of O2 during assay. It was shown that 0.05 atm pC2H2 was adequate for routine 1-h assays of the soil system employed. Individual soil samples could be subjected to repeated 1-h assays (with removal of C2H2 and C2H4 by evacuation after each assay) thus avoiding side-effects of long exposure to C2H2.  相似文献   

13.

Purpose

Nitrous oxide (N2O) production and reduction rates are dependent on the interactions with each other and it is therefore important to evaluate them within the context of simultaneously operating N2O emission and reduction. The objective of this study was to quantify the simultaneously occurring N2O emission and reduction across a range of subtropical soils in China, to gain a mechanistic understanding of potential N2O dynamics under the denitrification condition and their important drivers, and to evaluate the potential role of the subtropical soils as either sources or sinks of N2O through denitrification.

Materials and methods

Soils (45, from a range of different land uses and soil parent materials) were collected from the subtropical region of Jiangxi Province, China, and tested for their potential capacity for N2O emission and N2O reduction to N2 during denitrification. N2O emission and reduction were determined in a closed system under N2 headspace after the soils were treated with 200?mg?kg?1 NO 3 ? -N and incubation at 30?°C for 28?days. The soil physical and chemical properties, the temporal variations in headspace N2O concentration, and NO 3 ? -N and NH 4 + -N concentrations in the soil slurry were measured.

Results and discussion

Variations in N2O concentration (N) over incubation time (t) were consistent with an equation in which average R 2?=?0.84?±?0.11 (p?<?0.05): $ N = A \times \left( {1 - \exp \left( { - {k_1} \times t} \right)} \right) - B \times \exp \left( {{k_2} \times t} \right) $ , where A is the total N2O emission during the incubation, B is a constant, and k 1 and k 2 are the N2O emission constant and reduction constants, respectively. The results of the simulation showed that k 1 was greater than k 2. The reduced amount of NO 3 ? -N in the first 7?days of incubation and the N2O emission rate (the percentage of A value relative to the amount of NO 3 ? -N reduced during the 28-day incubation, R n) were able to explain 82.9?% (p?<?0.01) of the variation in total N2O emission (A) during the incubation for the soil samples studied, indicating that the total amount of N2O emitted was determined predominately by denitrification capacity. Soil organic carbon content and soil nitrogen mineralization are the key factors that determine differences in the amounts of reduced NO 3 ? -N among the soil samples. The R n value decreased with increasing k 2 (p?<?0.01), indicating that soils with higher N2O reduction capacity under these incubation conditions would emit less N2O per unit of denitrified NO 3 ? -N than the other soils. Results are valuable in the evaluation of net N2O emissions in the subtropical soils and the global N budget.

Conclusions

In a closed, anaerobic system, variations in N2O concentration in the headspace over the incubation time were found to be compatible with a nonlinear equation. Soil organic carbon and the amount of NH 4 + -N mineralized from the organic N during the first 7?days of incubation are the key factors that determine differences in the N2O emission constant (k 1), the N2O reduction constant (k 2), the total N2O emission during the incubation (A) and the N2O emission rate (R n).  相似文献   

14.
Acetylene reduction activity (ARA) was measured in cores containing roots of various Israeli wild and cultivated wheat lines colonized by Azospirillum. The inoculated plants were grown under greenhouse or field conditions. Although, no measurable ARA was detected during earlier stages of wheat development, 50–600 nmol C2H4 g?1 dry root h?1 was measured during heading and flowering stages. By using N yield balance and 15N dilution techniques, it was found that Triticum aestivum cv. Miriam inoculated with Azospirillum accumulated 20% more N (14N and 15N) at the booting stage than did the uninoculated control. This difference in N content became less apparent in grains. No significant 15N dilution could be found and the contribution of atmospheric N2 to the N content of grains of inoculated plants was negligible. It was concluded that the potential contribution of biological N2 fixation to spring wheat cultivation in Israel is very low.  相似文献   

15.
By addition of phenol at concentrations between 0.1 and 10 mmol·l?1, nitrogenase activity (acetylene reduction assay) is enhanced by a factor of 5 in the rhizosphere of Pennisetum glaucum (pearl millet) incubated under 20% O2. No increase is found under microaerobic conditions. This enhancement effect is also noticed in a soil amended with a sucrose concentration of 20 mmol·l?1. Under those conditions, however, an enhancement is found under aerobic as well as under microaerobic conditions and a further increase of the phenol added reduces the activity to almost zero. A 4-fold increase of N2-fixation by phenol addition under aerobic conditions was determined with homogenous sediments from a fresh water lake while anaerobic N2-fixation was already slightly reduced by the same concentration added. Excised roots of Sorghum nutans CSH 5 failed to show any phenol enhancement of nitrogenase activity. After a preincubation of 6h, inhibition of nitrogenase activity under air by addition of 1 mmol·l?1 was much more pronounced than under microaerobic conditions.  相似文献   

16.
Tropospheric ozone (O3) has long been documented to cause an injury to plants, but a plants’ protectant, widely applicable in agronomical practice, does not exist. We evaluated the potential antiozonate efficacy of the antitranspirant di-1-p-menthene (Vapor Gard) compared with ethylenediurea (EDU) on Bel-W3 tobacco plants. Plants were treated either with water, or by EDU (10, 100, and 500 mg dm?3), or by vapor (1, 5, 10, and 50 ml dm?3) and were exposed either to O3-enriched (90 ppb) or O3-free air, for 12 days and 8 h day?1. EDU when applied at 10 mg dm?3 did not protect the plants against O3, but when applied at 100 and 500 mg dm?3 offered a significant protection to the plants. Vapor, when applied at 1 ml dm?3 did not protect the plants against O3, neither by terms of foliar visible injury nor by terms of aboveground biomass. In addition, when applied at 10 and 50 ml dm?3 caused phytotoxicity to all the plants, which it was expressed as necrotic spots on the leaves’ surface, misshaping of the leaves, or short plants' height. It is obvious that vapor does not protect Bel-W3 tobacco plants against O3. The antiozonate role of di-1-p-menthene is species-specific and probably occurs only under short-term exposures.  相似文献   

17.
It has been suggested that soil-thawing and snow-melting are critical triggers for vigorous emissions of nitrous oxide (N2O) from soils in cold regions. However, because soil freezing is affected by air temperature and snow cover, accurate predictions that estimate subsequent emissions of this important greenhouse gas are difficult to make. In this study, we measured in situ soil gas N2O and oxygen (O2) concentrations at two experimental sites in northern Japan over the period of a year, from November 2008 to October 2009, to clarify the factors stimulating N2O production in soil at low temperatures. The sites were N-fertilized bare arable lands with different soil frost depths and snowmelt rates, according to the snow cover management imposed. Winter-to-spring net N2O fluxes, ranging from −0.10 to 1.95 kg N2O-N ha−1, were positively correlated with the annual maximum soil frost depth (ranging from 0.03 to 0.41 m; r = 0.951***). In the plots with deeper maximum soil frost, winter-to-spring N2O fluxes represented 58% to 85% of the annual values. Soil N2O production was stimulated when the soil frost depth was greater than 0.15 m or the daily mean soil temperature at 0.05-m depth was below −2.0 °C. In the soil with the greatest frost depth, soil gas N2O concentrations at the depth of 0.10 m peaked at 46 ppm when soil gas O2 concentrations fell down to 0.12 m3 m−3 under soil temperature below 0.0 °C. Snowmelt acceleration had no stimulating effect on N2O production in the soil during the winter-to-spring period.  相似文献   

18.
Loblolly pine seedlings of five half-sib families were grown under ambient, subambient (approximately 0.6 × ambient), and elevated [ambient + 60 ppb O3 (120 μg m?3)] O3 levels for one growing season in open-topped chambers. Diameter and height of the seedlings were measured periodically over the growing season, and above ground and below ground biomass were determined at harvest. Significant genetic differences were found in above ground volume (D 2H) 1 mo after 03 fumigation began and continued until harvest. Biomass of secondary needles and coarse and fine roots also differed significantly among families. Elevated O3 resulted in significantly decreased D 2H and secondary needle biomass relative to seedlings grown in ambient air. Seedlings receiving subambient O3 levels were intermediate in size, but were not significantly different from seedlings fumigated at ambient O3 levels. Root and stem biomass did not differ significantly among treatments. A significant interaction of O3 and genotype was detected, suggesting that the response of loblolly pine to O3 is influenced by genotype.  相似文献   

19.
Potassium (K) uptake rates were determined for Marianna 2624 rootstocks with ‘French’ prune scions using the nutrient solution depletion technique. The nutrient solutions were bubbled with factorial combinations of nitrogen (N2), oxygen (O2), and carbon dioxide (CO2) to create treatment root atmospheres with O2 ranging from 0.01 to 0.10 m3/m3 and CO2 ranging from 0 to 0.05 m3/m3. The K+ uptake rate was more susceptible to O2 deprivation than to elevated CO2 in the root atmosphere. Decreasing O2 levels from 0.10 m3/m3 decreased K+ uptake in a hyperbolic fashion to no net uptake at 0.01 m3/m3 O2. Increasing root atmosphere CO2 from 0 to 0.05 m3/m3 had a small depressing effect on net K+ influx from 60 μM K+ solutions at 0.10 and 0.05 m3/m3 O2, but no effect when O2 was 0.025 or 0.01 m3/m3. Elevating CO2 decreased Km for the net K+ influx rate at 0.10 and 0.05 m3/m3 O2. Increased pH buffering from higher HCO3 concentration at the plasma membrane surface was suggested to explain the CO2 effect on Km.  相似文献   

20.
Methanotrophy of arable soils is affected by N fertilization, but the knowledge about the effect of oxygen level is poorly understood; soil aeration can fluctuate and zones of low oxygen are widespread in soil. We monitored CH4 oxidation in three mineral soils (Eutric Cambisol, Haplic Podzol, Mollic Gleysol) under laboratory conditions by varying the O2 level (from 20 to 2% O2), with or without NH4+ (100 mg N kg?1). In controls (without NH4+), CH4 was oxidized completely in the O2 range from oxia (20% O2) to high hypoxia (5% O2), while the process was inhibited under microoxia (2% O2). Ammonium application decreased CH4 consumption in all soils. This negative effect was stronger at 20% and 2% O2 than under hypoxia. The highest CH4 oxidation rates and the shortest initial (lag) phases in both control and NH4+-amended soils were observed under high (5% O2) and low (10% O2) hypoxia.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号