Enrichment of High-Affinity CO Oxidizers in Maine Forest Soil

Carboxydotrophic activity in forest soils was enriched by incubation in a flowthrough system with elevated concentrations of headspace CO (40 to 400 ppm). CO uptake increased substantially over time, while the apparent K_m (_appK_m) for uptake remained similar to that of unenriched soils (<10 to 20 ppm). Carboxydotrophic activity was transferred to and further enriched in sterile sand and forest soil. The _appK_ms for secondary and tertiary enrichments remained similar to values for unenriched soils. CO uptake by enriched soil and freshly collected forest soil was inhibited at headspace CO concentrations greater than about 1%. A novel isolate, COX1, obtained from the enrichments was inhibited similarly. However, in contrast to extant carboxydotrophs, COX1 consumed CO with an _appK_m of about 15 ppm, a value comparable to that of fresh soils. Phylogenetic analysis based on approximately 1,200 bp of its 16S rRNA gene sequence suggested that the isolate is an α-proteobacterium most closely related to the genera Pseudaminobacter, Aminobacter, and Chelatobacter (98.1 to 98.3% sequence identity).     

Nitrate-dependent anaerobic carbon monoxide oxidation by aerobic CO-oxidizing bacteria

Two dissimilatory nitrate-reducing (Burkholderia xenovorans LB400 and Xanthobacter sp. str. COX) and two denitrifying isolates (Stappia aggregata IAM 12614 and Bradyrhizobium sp. str. CPP), previously characterized as aerobic CO oxidizers, consumed CO at ecologically relevant levels (<100 ppm) under anaerobic conditions in the presence, but not absence, of nitrate. None of the isolates were able to grow anaerobically with CO as a carbon or energy source, however, and nitrate-dependent anaerobic CO oxidation was inhibited by headspace concentrations >100-1000 ppm. Surface soils collected from temperate, subtropical and tropical forests also oxidized CO under anaerobic conditions with no lag. The observed activity was 25-60% less than aerobic CO oxidation rates, and did not appear to depend on nitrate. Chloroform inhibited anaerobic but not aerobic activity, which suggested that acetogenic bacteria may have played a significant role in forest soil anaerobic CO uptake.     

Soil-atmosphere CO exchanges and microbial biogeochemistry of CO transformations in a Brazilian agricultural ecosystem

Although anthropogenic land use has major impacts on the exchange of soil and atmosphere gas in general, relatively little is known about its impacts on carbon monoxide. We compared soil-atmosphere CO exchanges as a function of land use, crop type, and tillage treatment on an experimental farm in Par?na, Brazil, that is representative of regionally important agricultural ecosystems. Our results showed that cultivated soils consumed CO at rates between 3 and 6 mg of CO m(-2) day(-1), with no statistically significant effect of tillage method or crop. However, CO exchange for a pasture soil was near zero, and an unmanaged woodlot emitted CO at a rate of 9 mg of CO m(-2) day(-1). Neither nitrite, aluminum sulfate, nor methyl fluoride additions affected CO consumption by tilled or untilled soils from soybean plots, indicating that CO oxidation did not depend on ammonia oxidizers and that CO oxidation patterns differed in part from patterns reported for forest soils. The apparent K(m) for CO uptake, 5 to 11 ppm, was similar to values reported for temperate forest soils; V(max) values, approximately 1 micro g of CO g (dry weight)(-1) h(-1), were comparable for woodlot and cultivated soils in spite of the fact that the latter consumed CO under ambient conditions. Short-term (24-h) exposure to elevated levels of CO (10% CO) partially inhibited uptake at lower concentrations (i.e., 100 ppm), suggesting that the sensitivity to CO of microbial populations that are active in situ differs from that of known carboxydotrophs. Soil-free soybean and corn roots consumed CO when they were incubated with 100-ppm concentrations and produced CO when they were incubated with ambient concentrations. These results document for the first time a role for cultivated plant roots in the dynamics of CO in an agricultural ecosystem.     

Attributes of atmospheric carbon monoxide oxidation by Maine forest soils

CO, one of the most important trace gases, regulates tropospheric methane, hydroxyl radical, and ozone contents. Ten to 25% of the estimated global CO flux may be consumed by soils annually. Depth profiles for (14)CO oxidation and CO concentration indicated that CO oxidation occurred primarily in surface soils and that photooxidation of soil organic matter did not necessarily contribute significantly to CO fluxes. Kinetic analyses revealed that the apparent K(m) was about 18 nM (17 ppm) and the V(max) was 6.9 micromol g (fresh weight)(-1) h(-1); the apparent K(m) was similar to the apparent K(m) for atmospheric methane consumption, but the V(max) was more than 100 times higher. Atmospheric CO oxidation responded sensitively to soil water regimes; decreases in water content in initially saturated soils resulted in increased uptake, and optimum uptake occurred at water contents of 30 to 60%. However, extended drying led to decreased uptake and net CO production. Rewetting could restore CO uptake, albeit with a pronounced hysteresis. The responses to changing temperatures indicated that the optimum temperature for net uptake was between 20 and 25 degrees C and that there was a transition to net production at temperatures above 30 degrees C. The responses to methyl fluoride and acetylene indicated that populations other than ammonia oxidizers and methanotrophs must be involved in forest soils. The response to acetylene was notable, since the strong initial inhibition was reversed after 12 h of incubation; in contrast, methyl fluoride did not have an inhibitory effect. Ammonium did not inhibit CO uptake; the level of nitrite inhibition was initially substantial, but nitrite inhibition was reversible over time. Nitrite inhibition appeared to occur through indirect effects based on abiological formation of NO.     

Soil-Atmosphere CO Exchanges and Microbial Biogeochemistry of CO Transformations in a Brazilian Agricultural Ecosystem

Although anthropogenic land use has major impacts on the exchange of soil and atmosphere gas in general, relatively little is known about its impacts on carbon monoxide. We compared soil-atmosphere CO exchanges as a function of land use, crop type, and tillage treatment on an experimental farm in Parãna, Brazil, that is representative of regionally important agricultural ecosystems. Our results showed that cultivated soils consumed CO at rates between 3 and 6 mg of CO m⁻² day⁻¹, with no statistically significant effect of tillage method or crop. However, CO exchange for a pasture soil was near zero, and an unmanaged woodlot emitted CO at a rate of 9 mg of CO m⁻² day⁻¹. Neither nitrite, aluminum sulfate, nor methyl fluoride additions affected CO consumption by tilled or untilled soils from soybean plots, indicating that CO oxidation did not depend on ammonia oxidizers and that CO oxidation patterns differed in part from patterns reported for forest soils. The apparent K_m for CO uptake, 5 to 11 ppm, was similar to values reported for temperate forest soils; V_max values, approximately 1 μg of CO g (dry weight)⁻¹ h⁻¹, were comparable for woodlot and cultivated soils in spite of the fact that the latter consumed CO under ambient conditions. Short-term (24-h) exposure to elevated levels of CO (10% CO) partially inhibited uptake at lower concentrations (i.e., 100 ppm), suggesting that the sensitivity to CO of microbial populations that are active in situ differs from that of known carboxydotrophs. Soil-free soybean and corn roots consumed CO when they were incubated with 100-ppm concentrations and produced CO when they were incubated with ambient concentrations. These results document for the first time a role for cultivated plant roots in the dynamics of CO in an agricultural ecosystem.     

Build up and depletion of soil phosphorus and potassium and their uptake by rice and wheat in a long-term field experiment

Summary In a field experiment initiated at the Central Soil Salinity Research Institute, Karnal in 1974 involving rice wheat cropping sequence and NPK fertilizer use on sodic soil (pH 9.2, ESP 32.0), an attempt was made to evaluate the available P and K status of the soil and their uptake by the crops during 1982–83 and 83–84.Application of P to either or both the crops significantly enhanced the yields of rice and improved available P status of the soil. Wheat yields remained unaffected. Fertilizer N reduced P content in rice but increased P uptake in crops and considerably brought down available P to a level (4.5 ppm) where rice plants showed reduced tillering and phosphorus deficiency. Application of K did not affect the yield of either crop but enhanced its available status in soil and uptake by the crops. Contribution of the non-exchangeable K towards total potassium removal was about 93% in the absence of applied K which decreased to 87% with the use of K. Application of K to both crops resulted in lesser uptake from non-exchangeable form as compared to its application to either crop. Laboratory studies carried out on soils of the experimental plots showed that cumulative K release measured after five successive extractions was higher in K-treated soils as compared to untreated ones. The major difference was only in the first extraction representing the exchangeable K after which release became independent of the available K of the soil.     

Effects of Environmental Parameters on the Formation and Turnover of Acetate by Forest Soils

The capacity to form acetate from endogenous matter was a common property of diverse forest soils when incubated under anaerobic conditions. At 15 to 20(deg)C, acetate synthesis occurred without appreciable delay when forest soils were incubated as buffered suspensions or in microcosms at various percentages of their maximum water holding capacity. Rates for acetate formation with soil suspensions ranged from 35 to 220 (mu)g of acetate per g (dry weight) of soil per 24 h, and maximal acetate concentrations obtained in soil suspensions were two- to threefold greater than those obtained with soil microcosms at the average water holding capacity of the soil. Cellobiose degradation in soil suspensions yielded H(inf2) as a transient product. Under anaerobic conditions, supplemental H(inf2) and CO(inf2) were directed towards the acetogenic synthesis of acetate, and enrichments yielded a syringate-H(inf2)-consuming acetogenic consortium. At in situ temperatures, acetate was a relatively stable anaerobic end product; however, extended incubation periods induced acetoclastic methanogenesis and sulfate reduction. Higher mesophilic and thermophilic temperatures greatly enhanced the capacity of soils to form methane. Although methanogenic and sulfate-reducing activities under in situ-relevant conditions were negligible, these findings nonetheless demonstrated the occurrence of methanogens and sulfate-reducing bacteria in these aerated terrestrial soils. In contrast to the protracted stability of acetate under anaerobic conditions at 15 to 20(deg)C with unsupplemented soils, acetate formed by forest soils was rapidly consumed in the presence of oxygen and nitrate, and substrate-product stoichiometries indicated that acetate turnover was coupled to oxygen-dependent respiration and denitrification. The collective results suggest that acetate formed under anaerobic conditions might constitute a trophic link between anaerobic and aerobic processes in forest soils.     

Microbial carbon monoxide consumption in salt marsh sediments

We have examined sediments from a fringing salt marsh in Maine to further understand marine CO metabolism, about which relatively little is known. Intact cores from the marsh emitted CO during dark oxic incubations, but emission rates were significantly higher during anoxic incubations, which provided evidence for simultaneous production and aerobic consumption in surface sediments. CO emission rates were also elevated when cores were exposed to light, which indicated that photochemical reactions play a role in CO production. A kinetic analysis of marsh surface sediments yielded an apparent K(m) of about 82 ppm, which exceeded values reported for well-aerated soils that consume atmospheric CO (65nM). Surface (0-0.2 cm depth interval) sediment slurries incubated under oxic conditions rapidly consumed CO, and methyl fluoride did not inhibit uptake, which indicated that neither ammonia nor methane oxidizers contributed to the observed activity. In contrast, aerobic CO uptake was inhibited by additions of readily available organic substrates (pyruvate, glucose and glycine), but not by cellulose. CO was also consumed by surface and sub-surface sediment slurries incubated under anaerobic conditions, but rates were less than during aerobic incubations. Molybdate and nitrate or nitrite, but not 2-bromoethanesulfonic acid, partially inhibited anaerobic uptake. These results suggest that sulfidogens and acetogens, but not dissimilatory nitrate reducers or methanogens, actively consume CO. Sediment-free plant roots also oxidized CO aerobically; rates for Spartina patens and Limonium carolinianum roots were significantly higher than rates for Spartina alterniflora roots. Thus plants may also impact CO cycling in estuarine environments.     

Functional diversity and community structure of micro-organisms in three arctic soils as determined by sole-carbon-source-utilization

Functional diversities of micro-organisms in arctic soils at three incubation temperatures were assessed using sole-carbon-source-utilization (SCSU). Soil samples were collected from an area of anthropogenic fertilization (mixed Dorset/Thule/Historic site), an area of animal enrichment (bird rock perches), and unaltered tundra (raised beach; control soil site). The micro-organisms were extracted from the soil samples and inoculated into Gram-negative (GN) Biolog plates incubated at 30°C, 10°C, and 4°C. Calculations of the Shannon index, substrate utilization richness, Shannon evenness, and the Jaccard coefficient of similarity were based upon substrate utilization on the Biolog plates. Principal component analysis distinguished microbial communities in enriched soils from unenriched soils. At 10°C and 4°C, Shannon indices of enriched soil microbial communities (10°C: soils influenced by wild animals=4.28, soils influenced by human activities=4.20; 4°C: soils influenced by wild animals=4.15, soils influenced by human activities=4.03) were significantly higher than unenriched soil microbial communities (10°C: 3.66; 4°C: 3.38). Substrate utilization richness and evenness displayed similar trends. Although Jaccard coefficients showed uniformity across the different soil samples, cluster analysis supported patterns demonstrated by PCA. Lower temperatures (4°C and 10°C) yielded greater resolution between soil microbial communities than 30°C based on Biolog colour development patterns.     

Enhanced biodegradation of methoxychlor in soil under sequential environmental conditions.

Ring-U-[14C]methoxychlor [1,1-bis(p-methoxyphenyl)-2,2,2-trichloroethane] was incubated in soil under aerobic and anaerobic conditions. Primary degradation of methoxychlor occurred under anaerobic conditions, but not under aerobic conditions, after 3 months of incubation. Analysis of soil extracts, using gas chromatography, demonstrated that only 10% of the compound remained at initial concentrations of 10 and 100 ppm (wt/wt) of methoxychlor. Evidence is presented that a dechlorination reaction was responsible for primary degradation of methoxychlor. Analysis of soils treated with 100 ppm of methoxychlor in the presence of 2% HgCl2 showed that 100% of the compound remained after 3 months, indicating that degradation in the unpoisoned flasks was biologically mediated. Methanogenic organisms, however, are probably not involved, as strong inhibition of methane production was observed in all soils treated with methoxychlor. During the 3-month incubation period, little or no evaluation of 14CO2 or 14CH4 occurred under either aerobic or anaerobic conditions. Cometabolic processes may be responsible for the extensive molecular changes which occurred with methoxychlor because the rate of its disappearance from soil was observed to level off after exhaustion of soil organic matter. After this incubation period, soils previously incubated under anaerobic conditions were converted to aerobic conditions. The rates of 14CO2 evolution from soils exposed to anaerobic and aerobic sequences of environments ranged from 10- to 70-fold greater than that observed for soils exposed solely to an aerobic environment.     

Response of atmospheric methane consumption by maine forest soils to exogenous aluminum salts

Atmospheric methane consumption by Maine forest soils was inhibited by additions of environmentally relevant levels of aluminum. Aluminum chloride was more inhibitory than nitrate or sulfate salts, but its effect was comparable to that of a chelated form of aluminum. Inhibition could be explained in part by the lower soil pH values which resulted from aluminum addition. However, significantly greater inhibition by aluminum than by mineral acids at equivalent soil pH values indicated that inhibition also resulted from direct effects of aluminum per se. The extent of inhibition by exogenous aluminum increased with increasing methane concentration for soils incubated in vitro. At methane concentrations of >10 ppm, inhibition could be observed when aluminum chloride was added at concentrations as low as 10 nmol g (fresh weight) of soil(-1). These results suggest that widespread acidification of soils and aluminum mobilization due to acid precipitation may exacerbate inhibition of atmospheric methane consumption due to changes in other parameters and increase the contribution of methane to global warming.     

NUTRITIONAL STUDIES OF TWO RED ALGAE. I. GROWT RATE AS A FUNCTION OF NITROGEN SOURCE AND CONCENTRATION1

Gracilaria foliifera (Forsskal) Borgesen and Neoagardhiella bailiyi (Harvey ex Kiitzing) Wynne & Taylor were grown in continuous-flow culture under controlled environmental conditions in 15 liter experimental chambers. Growth rate was related to the source and concentration of nitrogen enrichment supplied to the plants, Growth rate appeared to follow saturation-type nutrient uptake kinetics for plants receiving ammonium, nitrate, urea of sewage effluent enrichments. Ammonium enrichment produced higher growth rates than nitrate of sewage enrichment. The lowest growth rates occurred in the chambers receiving unenriched seawater or urea. The low estimated constants (K) for growth were in the range of 0.2–0.4 (M N for all N enrichments examined. The low estimated values of K compare closely with those found for microalgae and indicate that both species possess the ability to utilize very low concentrations of N.     

The phylogenetic distribution and ecological role of carbon monoxide oxidation in the genus Burkholderia

Burkholderia is a physiologically and ecologically diverse genus that occurs commonly in assemblages of soil and rhizosphere bacteria. Although Burkholderia is known for its heterotrophic versatility, we demonstrate that 14 distinct environmental isolates oxidized carbon monoxide (CO) and possessed the gene encoding the catalytic subunit of form I CO dehydrogenase (coxL). DNA from a Burkholderia isolate obtained from a passalid beetle also contained coxL as do the genomic sequences of species H160 and Ch1-1. Isolates were able to consume CO at concentrations ranging from 100 ppm (vol/vol) to sub-ambient (< 60 ppb (vol/vol)). High concentrations of pyruvate inhibited CO uptake (> 2.5 mM), but mixotrophic consumption of CO and pyruvate occurred when initial pyruvate concentrations were lower (c. 400 lM). With the exception of an isolate most closely related to Burkholderia cepacia, all CO-oxidizing isolates examined were members of a nonpathogenic clade and were most closely related to Burkholderia species, B. caledonica, B. fungorum, B. oxiphila, B. mimosarum, B. nodosa, B. sacchari, B. bryophila, B. ferrariae, B. ginsengesoli, and B. unamae. However, none of these type strains oxidized CO or contained coxL based on results from PCR analyses. Collectively, these results demonstrate that the presence of CO oxidation within members of the Burkholderia genus is variable but it is most commonly found among rhizosphere inhabitants that are not closely related to B. cepacia.     

Isolation and Characterization of Iron and Sulfur-Oxidizing Bacteria from Maiduk Copper Mine at Shahrbabk Province in Iran

Microbial oxidation of iron and sulfur are important steps in biogeochemical cycles in mining environments. The aim of this study was the enrichment and identification of two important groups of bacteria that are involved in bioleaching of copper ores. Some soil samples were collected from the Maiduk copper mine. Iron-oxidizing bacteria were enriched in 9K medium containing ferrous sulfate, and sulfur oxidizers were enriched in 9K medium containing powdered sulfur instead of ferrous sulfate as energy source. After three subcultures, autotrophic bacteria were isolated on 9K agarose medium with appropriate energy sources. The autotrophic bacteria from the enrichments were identified by amplification of 16S rRNA gene and sequencing. Bioleaching experiments were performed in 100 ml of 9K medium containing 5 g of low-grade copper ore instead of ferrous sulfate. Twelve different iron and sulfur-oxidizing bacteria were isolated from the collected soil samples of Maiduk copper mine. Molecular identification indicated that two prevalent strains in the ore enrichments could be assigned to the Acidithiobacillus ferooxidans strain HGM and the Thiobacillus thioparus strain HGE. These two strains reached their logarithmic phase of growth after 8 days of incubation in their respective media at 30°C. Of these two cultures, strain HGM leached more copper ore (300 ppm) from the Maiduk copper ore than did strain HGE (200 ppm). Application of these two strains to the Maiduk copper ore in situ and to ore heaps should improve the leaching process.     

Effects of toxic heavy metals (Cd,Pb) on growth and mineral nutrition of beech (Fagus sylvatica L.)

The beech (Fagus sylvatica L.) is the dominant tree in Middle Europe under many different ecological conditions. But like other tree species, it is suffering in the last ten years increasingly by air pollutants including heavy metals which have been deposited and accumulated for decades in many forest soils. Increasingly mobilized by acidification processes, these metals may have toxic effects on trees.In autecological studies (dose-response-experiments) effects of root-applied Pb and Cd on various growth parameters, on uptake of mineral nutrients and on transpiration of young beech trees were evaluated, and critical concentrations (threshold levels) could be established. Significant leaf area reduction was found with 6 ppm Pb (0.3 ppm Cd) in the leaves (DW), but biomass reduction only with 18 ppm Pb (3.6 ppm Cd). Root elongation rates of seedlings were significantly reduced with 44 ppm plant-available Pb in the soil by about 30%, but only with 24 ppm Pb when combined with 2 ppm Cd, exhibiting synergistic effects. After treatments with 20 ppm Pb and 1 ppm Cd in sand culture, a considerable decrease in the contents of K, Ca, Mg, Fe, Mn, and Zn in roots and leaves of saplings was coincident with high (roots) and moderate (leaves) accumulation of Pb and Cd. A 20% reduction of transpiration rates was measured in ten-year-old beech trees after three months of exposure to a forest soil containing 2.5 ppm plant-available Cd.The data indicate that present-day concentrations mainly of Pb, but not yet of Cd, in acidified European forest soils are sufficiently high to affect germination, growth and mineral nutrition of natural rejuvenation of beech.The data published here are part of a doctoral and of various diploma theses: Mrs. Christiane Bertels, Barbara Buschmann, Martina Hücker, Gritli Noack, Ute Röder, Swantje von Oy and Mr. Rüdiger Ahrend, Peter Rüther and Frank Weisser.     

Starvation alters the apparent half-saturation constant for methane in the type II methanotroph Methylocystis strain LR1

When cells of a type II methanotrophic bacterium (Methylocystis strain LR1) were starved of methane, both the K(m(app)) and the V(max(app)) for methane decreased. The specific affinity (a(o)(s)) remained nearly constant. Therefore, the decreased K(m(app)) in starved cells was probably not an adjustment to better utilize low-methane concentrations.     

Attributes of Atmospheric Carbon Monoxide Oxidation by Maine Forest Soils

CO, one of the most important trace gases, regulates tropospheric methane, hydroxyl radical, and ozone contents. Ten to 25% of the estimated global CO flux may be consumed by soils annually. Depth profiles for ¹⁴CO oxidation and CO concentration indicated that CO oxidation occurred primarily in surface soils and that photooxidation of soil organic matter did not necessarily contribute significantly to CO fluxes. Kinetic analyses revealed that the apparent K_m was about 18 nM (17 ppm) and the V_max was 6.9 μmol g (fresh weight)⁻¹ h⁻¹; the apparent K_m was similar to the apparent K_m for atmospheric methane consumption, but the V_max was more than 100 times higher. Atmospheric CO oxidation responded sensitively to soil water regimes; decreases in water content in initially saturated soils resulted in increased uptake, and optimum uptake occurred at water contents of 30 to 60%. However, extended drying led to decreased uptake and net CO production. Rewetting could restore CO uptake, albeit with a pronounced hysteresis. The responses to changing temperatures indicated that the optimum temperature for net uptake was between 20 and 25°C and that there was a transition to net production at temperatures above 30°C. The responses to methyl fluoride and acetylene indicated that populations other than ammonia oxidizers and methanotrophs must be involved in forest soils. The response to acetylene was notable, since the strong initial inhibition was reversed after 12 h of incubation; in contrast, methyl fluoride did not have an inhibitory effect. Ammonium did not inhibit CO uptake; the level of nitrite inhibition was initially substantial, but nitrite inhibition was reversible over time. Nitrite inhibition appeared to occur through indirect effects based on abiological formation of NO.     

Responses of Methanotrophic Activity in Soils and Cultures to Water Stress

Diffusive gas transport at high water contents and physiological water stress at low water contents limited atmospheric methane consumption rates during experimental manipulations of soil water content and water potential. Maximum rates of atmospheric methane consumption occurred at a soil water content of 25% (grams per gram [dry weight]) and a water potential of about -0.2 MPa. In contrast, uptake rates were highest at a water content of 38% and a water potential of -0.03 MPa when methane was initially present at 200 ppm. Uptake rates of atmospheric and elevated methane decreased when water potentials were reduced by adding either ionic or nonionic solutes to soils with a fixed water content. Uptake rates during these manipulations were lower when sodium chloride or potassium chloride was used to adjust water potential rather than sucrose. The response of methane consumption by soils to water potential was somewhat less pronounced than the response of methanotrophic cultures (e.g., Methylosinus trichosporium OB3b, Methylomonas rubra [= M. methanica], an isolate from a freshwater peat, and an isolate from an intertidal marine mudflat). However, unlike soils, methanotrophic cultures exhibited a stronger adverse response to nonionic solutes than to sodium chloride.     

Endogenous methanogenesis stimulates oxidation of atmospheric CH(4) in alpine tundra soil

Experiments were done to test the hypothesis that atmospheric CH(4) oxidizers in a well-drained alpine tundra soil are supported by CH(4) production from anaerobic microsites in the soil. Soil was subjected to 22 days of anaerobic conditions with elevated H(2) and CO(2) in order to stimulate methanogenesis. This treatment stimulated subsequent atmospheric CH(4) consumption, probably by increasing soil methanogenesis. After removal from anaerobic conditions, soils emitted CH(4) for up to 6 h, then oxidized atmospheric CH(4) at 111 (+/- 5.7) pmol (g dry weight)(-1) h(-1), which was more than 3 times the rate of control soils. Further supporting our hypothesis, additions of lumazine, a highly specific inhibitor of methanogenesis, prevented the stimulation of atmospheric CH(4) oxidation by the anaerobic treatment. The method used to create anaerobic conditions with elevated H(2) and CO(2) also elevated headspace CH(4) concentrations. However, elevated CH(4) concentrations under aerobic conditions did not stimulate CH(4) oxidation as much as preexposure to H(2) and CO(2) under anaerobic conditions. Anaerobic conditions created by N(2) flushing did not stimulate atmospheric CH4 oxidation, probably because N2 flushing inhibited methanogenesis by removing necessary precursors for methane production. We conclude that anaerobic conditions with elevated H(2) and CO(2) stimulate atmospheric CH(4) oxidation in this dry alpine tundra soil by increasing endogenous CH(4) production. This effect was prevented by inhibiting methanogenesis, indicating the importance of endogenous CH(4) production in a CH(4-) consuming soil.     

Use of strontium isotopes and foliar K content to estimate weathering of biotite induced by pine seedlings colonised by ectomycorrhizal fungi from two different soils

Pinus sylvestris seedlings, colonised by ectomycorrhizal (EM) fungi from either of two different soils (untreated forest soil and a limed soil from a clear cut area), were grown with or without biotite as a source of K. The biotite was naturally enriched in ⁸⁷Sr and the ratio of ⁸⁷Sr/ ⁸⁶Sr in the plant biomass was estimated and used as a marker for biotite weathering and compared to estimates of weathering based on foliar content of K. Different nutrient regimes were used to expose the seedlings to deficiencies of K with and without an application of nitrogen (NH₄NO₃) in excess of seedling demand. The seedlings were grown for 220 days and the elemental composition of the shoots were analysed at harvest. The EM colonisation was followed by analysing the concentration of ergosterol in the roots and the soils. Bacterial activity of the soil was estimated by the thymidine incorporation technique. The concentration of organic acids in the soil solution was measured in the soil in which seedlings colonised by EM fungi from the untreated forest soil were grown. It was found that seedlings colonised by EM fungi from untreated forest soil had taken up more K in treatments with biotite addition compared to seedlings colonised by EM fungi from the limed forest soil (p<0.05). Seedlings from untreated forest soil had larger shoots and contained more K when grown with biotite compared to KCl as K source, indicating that biotite had a stimulatory effect on the growth of these seedlings which was not related to K uptake. Seedlings from the limed soil, on the other hand, had similar foliar K content when grown with either biotite or KCl as K source. The larger uptake of K in seedlings from untreated forest soil was not an effect of a more developed EM colonisation of the roots since seedlings from the limed soil had a higher ergosterol concentration both in the soil and in the roots. Nutrient regimes had no significant influence on the total uptake of K but the ⁸⁷Sr/ ⁸⁶Sr isotope ratio in the plant biomass indicated that seedlings grown with excess nitrogen supply had taken up proportionally less Sr from the biotite (1.8% of total Sr content) compared to seedlings grown with a moderate nitrogen supply (5.0%). Furthermore, seedlings grown with excess nitrogen supply had a reduced fungal colonisation of roots and soil and bacterial activity was lower in these soils. The ⁸⁷Sr/ ⁸⁶Sr ratio in the plant biomass was positively correlated with fungal colonisation of the roots (r ²=0.98), which may indicate that the fungus was involved in releasing Sr from the biotite. Uptake of K from biotite was not related to the amount of organic acids in the soil solution. Oxalic acid was positively related to the amount of ergosterol in the root, suggesting that oxalic acid in the soil solution originates from the EM symbionts. The accuracy of the estimations of biotite weathering based on K uptake by the seedlings in comparison with the ⁸⁷Sr/⁸⁶Sr isotope ratio measured in the shoots is discussed. This revised version was published online in June 2006 with corrections to the Cover Date.