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1.
2.
Addition of five types of organic matter to Lake Washington sediments resulted in release of high concentrations of iron, organic carbon, and manganese into the interstitial water, and caused an increase in observed sediment oxygen consumption rates. The depressed electrode potentials (Eh < —150 mV) that should accompany such reduction processes did not occur, indicating that Eh was being poised by redox systems present in the sediment. Iron redox systems [Fe(OH)3‐Fe2+, Fe3(OH)8‐Fe2+, and Fe(OH)3‐Fe3(OH)8] were shown to be poising the Eh of control sediments throughout 13 weeks of incubation and dominating the potential of several of the organically amended sediments following the first three weeks of incubation. Depression of calculated iron system Eo values relative to that of the control sediment early in the incubation appeared to be due to the decreased pH and non‐equilibrium conditions in the organic matter‐amended sediment during the first weeks of incubation. Manganese redox systems exerted no discernable impact on the Eh of the sediment. 相似文献
3.
Over a period of three years (1990–1992) microbial biomass-C (Cmic), CO2 evolution, the Cmic:Corg ratio and the metabolic quotient for CO2 (qCO2) were determined in a Norway spruce stand (Höglwald) with experimentally acid-irrigated and limed plots since 1984. A clear relationship between soil pH and the level of microbial biomass-(Cmic) was noted, Cmic increasing with increasing soil pH in Oh or Ah horizons. More microbial biomass-C per unit C{org} (Cmic:Corg ratio) was detected in limed plots with elevated pH of Oh or Ah horizons as compared to unlimed plots with almost 3 times more Cmic per unit Corg in the limed Oh horizon. Differences here are significant at least at the p=0.05 level. The positive effects of liming (higher pH) on the Cmic:Corg ratio was more pronounced in the upper horizon (Oh)). The total CO2 evolution rate of unlimed plots was only half of that noted for limed plots which corresponded to the low microbial biomass levels of unlimed plots. The specific respiratory activity, qCO2, was similar and not significantly different between the unlimed control plot and the limed plot.Acid irrigation of plots with already low pH did not significantly affect the level of microbial biomass, the Cmic:Corg ratio or qCO2. An elevated qCO2 could be seen, however, for the limed + acid irrigated plot. The biomass seemed extremely stressed, showing with 3.8 g CO2-C mg-1 Cmic h-1 (Oh) the highest qCO2 value of all treatments. This was interpreted as a reflection of the continuous adaptation processes to the H+ ions by the microflora. The negative effect of acid irrigation of limed plots was also manifested in a decreased Cmic:Corg ratio. 相似文献
4.
Vertical stratification in sediments from a young oligotrophic South African impoundment: implications in phosphorus cycling 总被引:2,自引:2,他引:0
Changes at the mud surface in Midmar Dam, following impoundment, were studied by examining vertical profiles of selected parameters in sediment cores. Distinct stratification in organic carbon, pH and exchangeable Al3+ was evident. Phosphate adsorption characteristics in the stratified sediments was quantified using Langmuir adsorption isotherms. The adsorption maxima and bonding energy constants in the surface sediments (0–3 cm) were markedly lower than those below 3 cm, indicating that the surface layers are less efficient at binding phosphate than the deeper layers. Radiotracer experiments indicate that the layers comprising the top 3 cm of sediment predominate in PO4-P exchange with the overlying water. 相似文献
5.
Potential rates of nitrification and denitrification in an oligotrophic freshwater sediment system 总被引:1,自引:0,他引:1
Potential rates of nitrification and denitrification were measured in an oligotrophic sediment system. Nitrification potential was estimated using the CO oxidation technique, and potential denitrification was measured by the acetylene blockage technique. The sediments demonstrated both nitrifying and denitrifying activity. Eh, O2, and organic C profiles showed two distinct types of sediment. One type was low in organic C, had high O2 and Eh, and had rates of denitrification 1,000 times lower than the other which had high organic C, low O2, and low Eh. Potential nitrification and denitrification rates were negatively correlated with Eh. This suggests that environmental heterogeneity in denitrifier and nitrifier populations in oligotrophic sediment systems may be assessed using Eh before sampling protocols for nitrification or denitrification rates are established. There was no correlation between denitrification and nitrification rates or between either of these processes and NH4
+ or NO3
– concentrations. The maximum rate of denitrification was 0.969 nmole N cm–3 hour–1, and the maximum rate of nitrification was 23.6 nmole cm–3 hour–1, suggesting nitrification does not limit denitrification in these oligotrophic sediments. Some sediment cores had mean concentrations of 6.0 mg O2/liter and still showed both nitrification and denitrification activity. 相似文献
6.
The construction of three dams induced large changes in the tide range in the Eastern Scheldt, a tidal inlet in the southwestern part of the Netherlands. In 1986 the mean high tide level was reduced by almost one metre. This excluded the greater part of the medium-high marshes almost completely from tidal flooding.The absence of tidal flooding in the summer of 1986, combined with a net precipitation deficit, increased the bulk density of the sediment irreversibly from 400 to 530 kg m–3 in the top 5 cm. The subsidence of the backmarshes varied from 1 to 8 cm.The loss of moisture allowed oxygen to diffuse into the initial reducing sediment. This altered the geochemistry of the sediment significantly. The redoxcline was lowered from a mean depth of about 15 cm in 1985 to 20–30 cm in the summer of 1986. Evidence of pyrite oxidation within a narrow depth interval of 15–30 cm was obtained from the change in the composition of pore waters. The rapid increase in redox potentials (up to 600 mV) and total dissolved iron (up to 5 mM 1–1) and SO
inf4
sup2–
(up to 65 mM 1–1) and the decrease in pH (up to 4.5–2.5) all suggest a rapid oxidation of pyrite. Acidic conditions were found only in sediments with low contents of calcium carbonate and high contents of pyrite. The importance of seasonal changes in redox processes on the partial decalcification of the salt marsh sediments is discussed.The established of a new tide range was reflected in the pH and Eh of the sediment. In December 1987 the depth profiles of pH and Eh were again close to those observed in 1985. 相似文献
7.
Ucides cordatus is an abundant mangrove crab in Brazil constructing burrows of up to 2 m depth. Sediment around burrows may oxidize during low tides. This increase in sediment-air contact area may enhance carbon degradation processes. We hypothesized that 1) the sediment CO2 efflux rate is greater with burrows than without and 2) the reduction potential in radial profiles in the sediment surrounding the burrows decreases gradually, until approximating non-bioturbated conditions. Sampling was conducted during the North Brazilian wet season at neap tides. CO2 efflux rates of inhabited burrows and plain sediment were measured with a CO2/H2O gas analyzer connected to a respiration chamber. Sediment redox potential, pH and temperature were measured in the sediment surrounding the burrows at horizontal distances of 2, 5, 8 and 15 cm at four sediment depths (1, 10, 30 and 50 cm) and rH values were calculated. Sediment cores (50 cm length) were taken to measure the same parameters for plain sediment. CO2 efflux rates of plain sediment and individual crab burrows with entrance diameters of 7 cm were 0.7–1.3 µmol m−2 s−1 and 0.2–0.4 µmol burrows−1 s−1, respectively. CO2 released from a Rhizophora mangle dominated forest with an average of 1.7 U. cordatus burrows−1 m−2 yielded 1.0–1.7 µmol m−2 s−1, depending on the month and burrow entrance diameter. Laboratory experiments revealed that 20–60% of the CO2 released by burrows originated from crab respiration. Temporal changes in the reduction potential in the sediment surrounding the burrows did not influence the CO2 release from burrows. More oxidized conditions of plain sediment over time may explain the increase in CO2 release until the end of the wet season. CO2 released by U. cordatus and their burrows may be a significant pathway of CO2 export from mangrove sediments and should be considered in mangrove carbon budget estimates. 相似文献
8.
Populations of Methane-Producing Bacteria and In Vitro Methanogenesis in Salt Marsh and Estuarine Sediments 总被引:5,自引:5,他引:0
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Most probable numbers (MPNs) of methanogens in various salt marsh and estuarine sediments were determined with an anaerobic, habitat-simulating culture medium with 80% H2 plus 20% CO2 as substrate. Average MPNs for the short Spartina (SS) marsh sediments of Sapelo Island, Ga., were maximal at the 5- to 7-cm depth (1.2 × 107/g of dry sediment). Populations decreased to approximately 880/g of dry sediment at the 34- to 36-cm depth. There was no significant difference between summer and winter populations. In tall Spartina (TS) marsh sediments, average populations were maximal (1.2 × 106/g of dry sediment) in the upper 0- to 2-cm zone; populations from the 5- to 36-cm zones were similar (average of 9 × 104/g of dry sediment). Methanogenic populations for TS sediments of James Island Creek marsh, Charleston, S.C., were similar (average of 3 × 106/g of dry sediment) for all depths tested (0 to 22 cm), which was comparable to the trend observed for TS sediments at Sapelo Island, Ga. Sediment grab samples collected along a transect of James Island Creek and its adjacent Spartina marsh had MPNs that were approximately 20 times greater for the region of Spartina growth (average of 106/g of dry sediment) compared with the channel (approximately 5 × 104 methanogens per g of dry sediment). A similar trend was found at Pawley's Island marsh, S.C., but populations were approximately one order of magnitude lower. In vitro rates of methanogenesis with SS sediments incubated under 80% H2-20% CO2 showed that the 5- to 7-cm region exhibited maximal activity (51 nmol of CH4 g−1 h−1), which was greater than rates for sediments above and below this depth. SS sediment samples (5 to 7 cm) incubated under 100% N2 and supplemented with formate exhibited rates of methanogenesis similar to those generated by samples under 80% H2-20% CO2. Replacing the N2 atmosphere with H2 resulted in an eightfold decrease in the rate of methanogenesis. In vitro methanogenic activity by TS salt marsh sediments, incubated under 80% H2-20% CO2, was similar for all depths tested (0 to 22 cm). TS sediment samples (0 to 7 cm) supplemented with formate and incubated under 100% N2 had greater rates of methanogenesis compared with unsupplemented samples. 相似文献
9.
Bente Foereid Lorna A. Dawson David Johnson J. Ignacio Rangel-Castro 《Plant and Soil》2006,287(1-2):301-311
Knowledge of the fate of plant assimilate is fundamental to our understanding of the terrestrial carbon cycle, particularly if we are to predict the effects of changes in climate and land management practices on agroecosystems. Pulse-labelling experiments have revealed that some of the carbon fixed by plants is rapidly allocated below-ground and released back into the atmosphere in respiration. However, little is known about the fate of plant assimilate, not accounted for in soil respiration, in the longer term and how current management practices such as liming may affect this. In southern Scotland, UK, limed and unlimed acid grassland plots were pulse-labelled with 13CO2 and the turnover of 13C was studied one and two years after labelling. In this study the amount of labelled carbon remaining in shoot, root, and bulk soil pools, and how this differed between limed and unlimed plots was investigated. The results indicated that plant-root turnover was faster, and plants invested less nitrogen in the roots in the limed plots than in the unlimed plots. More 13C remained in the soil in the unlimed treatment compared to the limed treatment, but the main difference was found in the particulate organic matter, which turned over relatively quickly. The label was still above natural abundance one and two years after labelling in many cases. In addition, the results demonstrate that a 13CO2 pulse-label administered for only a few hours can be a useful approach for investigating turnover of carbon several years later. 相似文献
10.
The importance of isoetids for the exchange of dissolved inorganic nitrogen (DIN) between sediment and water was studied in shallow Lake Kvie, Denmark. Vegetated sediments from the littoral zone (55% of lake area) were compared to unvegetated sediments from the littoral and profundal zone. Clear effects of the isoetids were found on DIN in the porewater. At the vegetated station, NH4
+ showed the highest concentrations just below the surface (< 40 µM) whereas NO3
- was dominating below 5 cm depth with concentrations up to 100 µM during the spring. The unvegetated littoral sediment showed a distinct change between winter where NH4
+ dominated and summer where NO3
- was most abundant. NH4
+ dominated in the profundal sediment and showed increasing concentration with depth. The Eh was high (> 400 mV) in the vegetated sediment, indicating isoetid release of O2 in the rhizosphere. A low DIN uptake was observed at the vegetated station while, based on porewater data, a diffusive release from the sediment was expected. This difference was due to plant assimilation. In general a release of NH4
+ and an uptake of NO3
- was seen in all sediments. The denitrification rate calculated from the mass balance for the entire lake was 0.4 mmol m - 2 d-1 and accounted for removal of 77% of the annual N-input to Lake Kvie. 相似文献
11.
J.K. Fredrickson T.R. Garland R.J. Hicks J.M. Thomas S.W. Li K. M. McFadden 《Geomicrobiology journal》2013,30(1-2):53-66
Subsurface sediments obtained from three cores drilled to depths of 260 m below the surface in South Carolina were analyzed for heterotrophic bacteria; N2‐fixing microaerophiles; and nitrifying, sulfur‐oxidizing, and H2‐oxidizing lithotrophic bacteria. In addition, pore waters were extracted for chemical analysis of inorganic nitrogen species, sulfate, dissolved organic carbon, pH, and Eh. Autotroph populations were generally less than 103 most probable number (MPN) g‐1 dry sediment with sulfur‐oxidizing bacteria, detected in 60% of the sediment samples, being the most frequently encountered group. Nitrifying bacteria were detected mainly in sediments from one borehole (P28), and their populations in those sediments were correlated with pore‐water ammonium concentrations. Populations of heterotrophic bacteria in 60% of the sediments were greater than 106 colony forming units (CFU) g‐1 dry sediment and were typically lower in sediments of high clay content and low pH. Microaerophilic N2‐fixing bacteria were cultured from >50% and bacteria capable of growth on H2 were cultured from 35% of the subsurface sediments examined. Sediment texture, which controls porosity, water potential, and hydraulic conductivity, appears to be a major factor influencing microbial populations in coastal plain subsurface sediments. 相似文献
12.
Annual Pattern of Denitrification and Nitrate Ammonification in Estuarine Sediment 总被引:11,自引:2,他引:9
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Kirsten Schannong Jrgensen 《Applied microbiology》1989,55(7):1841-1847
The seasonal variation and depth distribution of the capacity for denitrification and dissimilatory NO3− reduction to NH4+ (NO3− ammonification) were studied in the upper 4 cm of the sediment of Norsminde Fjord estuary, Denmark. A combination of C2H2 inhibition and 15N isotope techniques was used in intact sediment cores in short-term incubations (maximum, 4 h). The denitrification capacity exhibited two maxima, one in the spring and one in the fall, whereas the capacity for NO3− ammonification was maximal in the late summer, when sediments were progressively reduced. The denitrification capacity was always highest in the uppermost 1 cm of the sediment and declined with depth. The NO3− ammonification was usually higher with depth, but the maximum activity in late summer was observed within the upper 1 cm. The capacity for NO3− incorporation into organic material was investigated on two occasions in intact sediment cores and accounted for less than 5% of the total NO3− reduction. Denitrification accounted for between 13 and 51% of the total NO3− reduction, and NH4+ production accounted for between 4 and 21%, depending on initial rates during the time courses. Changes of the rates during the incubation were observed in the late summer, which reflected synthesis of denitrifying enzymes. This time lag was eliminated in experiments with mixed sediment because of preincubation with NO3− and alterations of the near-environmental conditions. The initial rates obtained in intact sediment cores therefore reflect the preexisting enzyme content of the sediment. 相似文献
13.
Carbon flow in an upland grassland: effect of liming on the flux of recently photosynthesized carbon to rhizosphere soil 总被引:1,自引:0,他引:1
J. Ignacio Rangel-Castro † Jim I. Prosser Charlie M. Scrimgeour‡ Pete Smith† Nick Ostle§ Phil Ineson¶ y Meharg† Ken Killham† 《Global Change Biology》2004,10(12):2100-2108
The effect of liming on the flow of recently photosynthesized carbon to rhizosphere soil was studied using 13CO2 pulse labelling, in an upland grassland ecosystem in Scotland. The use of 13C enabled detection, in the field, of the effect of a 4‐year liming period of selected soil plots on C allocation from plant biomass to soil, in comparison with unlimed plots. Photosynthetic rates and carbon turnover were higher in plants grown in limed soils than in those from unlimed plots. Higher δ13C‰ values were detected in shoots from limed plants than in those from unlimed plants in samples clipped within 15 days of the end of pulse labelling. Analysis of the aboveground plant production corresponding to the 4‐year period of liming indicated that the standing biomass was higher in plots that received lime. Lower δ13C‰ values in limed roots compared with unlimed roots were found, whereas no significant difference was detected between soil samples. Extrapolation of our results indicated that more C has been lost through the soil than has been gained via photosynthetic assimilation because of pasture liming in Scotland during the period 1990–1998. However, the uncertainty associated with such extrapolation based on this single study is high and these estimates are provided only to set our findings in the broader context of national soil carbon emissions. 相似文献
14.
In anoxic salt marsh sediments of Sapelo Island, GA, USA, the vertical distribution of CH4 production was measured in the upper 20 cm of surface sediments in ten locations. In one section of high marsh sediments,
the concentration and oxidation of acetate in sediment porewaters and the rate and amount of14C acetate and14CO2 incorporation into cellular lipids of the microbial population were investigated. CH4 production rates ranged from <1 to 493 nM CH4 gram sediment−1 day−1 from intact subcores incubated under nitrogen. Replacement with H2 stimulated the rate of methane release up to nine fold relative to N2 incubations. Rates of lipid synthesis from CO2 averaged 39.2 ×10−2nanomoles lipid carbon cm3 sediment−1 hr−1, suggesting that CO2 may be an important carbon precursor for microbial membrane synthesis in marsh sediments under anoxic conditions. Qualitative
measurements of lipid synthesis rates from acetate were found to average 8.7 × 10−2 nanomoles. Phospholipids were the dominant lipids synthesized by both substrates in sediment cores, accounting for an average
of 76.6% of all lipid radioactivity. Small amounts of ether lipids indicative of methanogenic bacteria were observed in cores
incubated for 7 days, with similar rates of synthesis for both CO2 and acetate. The low rate of ether lipid synthesis suggests that either methanogen lipid biosynthesis is very slow or that
methanogens represent a small component of total microbial lipid synthesis in anoxic sediments.
present address: The University of Maryland,, Chesapeake Biological Laboratory, Box 38, Solomons, MD 20688, USA 相似文献
15.
In anoxic salt marsh sediments of Sapelo Island, GA, USA, the vertical distribution of CH4 production was measured in the upper 20 cm of surface sediments in ten locations. In one section of high marsh sediments,
the concentration and oxidation of acetate in sediment porewaters and the rate and amount of14C acetate and14CO2 incorporation into cellular lipids of the microbial population were investigated. CH4 production rates ranged from <1 to 493 nM CH4 gram sediment−1 day−1 from intact subcores incubated under nitrogen. Replacement with H2 stimulated the rate of methane release up to nine fold relative to N2 incubations. Rates of lipid synthesis from CO2 averaged 39.2 ×10−2nanomoles lipid carbon cm3 sediment−1 hr−1, suggesting that CO2 may be an important carbon precursor for microbial membrane synthesis in marsh sediments under anoxic conditions. Qualitative
measurements of lipid synthesis rates from acetate were found to average 8.7 × 10−2 nanomoles. Phospholipids were the dominant lipids synthesized by both substrates in sediment cores, accounting for an average
of 76.6% of all lipid radioactivity. Small amounts of ether lipids indicative of methanogenic bacteria were observed in cores
incubated for 7 days, with similar rates of synthesis for both CO2 and acetate. The low rate of ether lipid synthesis suggests that either methanogen lipid biosynthesis is very slow or that
methanogens represent a small component of total microbial lipid synthesis in anoxic sediments.
present address: The University of Maryland,, Chesapeake Biological Laboratory, Box 38, Solomons, MD 20688, USA 相似文献
16.
Shifts in the relative availability of phosphorus and nitrogen along estuarine salinity gradients 总被引:1,自引:0,他引:1
Phosphorus (P) availability in estuaries may increase with increasing salinity because sulfate from sea salt supports production of sulfide in sediments, which combines with iron (Fe) making it less available to sequester P. Increased P availability with increased salinity may promote the generally observed switch from P limitation of primary production in freshwater ecosystems to nitrogen (N) limitation in coastal marine waters. To investigate this hypothesis, we analyzed pore water from sediment cores collected along the salinity gradients of four Chesapeake Bay estuaries (the Patuxent, Potomac, Choptank, and Bush Rivers) with watersheds differing in land cover and physiography. At salinities of 1–4 in each estuary, abrupt decreases in pore water Fe2+ concentrations coincided with increases in sulfate depletion and PO4 3? concentrations. Peaks in water column PO4 3? concentrations also occur at about the same position along the salinity gradient of each estuary. Increases in pore water PO4 3? concentration with increasing salinity led to distinct shifts in molar NH4 +:PO4 3? ratios from >16 (the Redfield ratio characteristic of phytoplankton N:P) in the freshwater cores to <16 in the cores with salinities >1 to 4, suggesting that release of PO4 3? from Fe where sediments are first deposited in sulfate-rich waters could promote the commonly observed switch from P limitation in freshwater to N limitation in mesohaline waters. Finding this pattern at similar salinities in four estuaries with such different watersheds suggests that it may be a fundamental characteristic of estuaries generally. 相似文献
17.
Sediment Nitrification, Denitrification, and Nitrous Oxide Production in a Deep Arctic Lake 总被引:5,自引:4,他引:1
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We used a combination of 15N tracer methods and a C2H2 blockage technique to determine the role of sediment nitrification and denitrification in a deep oligotrophic arctic lake. Inorganic nitrogen concentrations ranged between 40 and 600 nmol · cm−3, increasing with depth below the sediment-water interface. Nitrate concentrations were at least 10 times lower, and nitrate was only detectable within the top 0 to 6 cm of sediment. Eh and pH profiles showed an oxidized surface zone underlain by more reduced conditions. The lake water never became anoxic. Sediment Eh values ranged from −7 to 484 mV, decreasing with depth, whereas pH ranged from 6.0 to 7.3, usually increasing with depth. The average nitrification rate (49 ng of N · cm−3 · day−1) was similar to the average denitrification rate (44 ng of N · cm−3 · day−1). In situ N2O production from nitrification and denitrification ranged from 0 to 25 ng of N · cm−3 · day−1. Denitrification appears to depend on the supply of nitrate by nitrification, such that the two processes are coupled functionally in this sediment system. However, the low rates result in only a small nitrogen loss. 相似文献
18.
Binding of phosphate in sediment accumulation areas of the eastern Gulf of Finland,Baltic Sea 总被引:1,自引:0,他引:1
The relationships between P and components binding P were studied by analysing the concentrations of N, P, Fe, Mn, Ca and Al in sediments and pore water along the estuarine transect of the River Neva in August 1995. The high sediment organic matter concentration resulted in low surface redox potential and high pore-water o-P concentration, whereas the abundance of amphipods resulted in high surface redox potentials and low pore-water o-P concentration. However, despite the variation in sediment organic matter and the abundance of amphipods, very reduced conditions and slightly variable concentrations of Tot-P (0.7–1.1 mg g–1 DW) were observed in the 10–15 cm sediment depth along the estuarine gradient, indicating that the pools of mobile P were largely depleted within the depth of 0–15 cm. Multiple regression analysis demonstrated that organic matter and Tot-Fe concentration of the sediment were closely related to the variation in Tot-P concentration of the sediments (r
2 = 0.817, n=32). In addition, the high total Fe:P ratio suggested that there is enough Fe to bind P in sediments along the estuarine gradient. However, low Fediss concentrations in the pore water of reduced sediment (redox-potential <–50 mV) indicated efficient precipitation of FeS (FeS and FeS2), incapable to efficiently bind P. Consequently, the low Fediss:o-P ratio (< 1) recorded in pore water in late summer implied that Fe3+ oxides formed by diffusing Fediss in the oxic zone of the sediments were insufficient to bind the diffusing o-P completely. The measured high o-P concentrations in the near-bottom water are consistent with this conclusion. However, there was enough Fediss in pore water to form Fe3+ oxides to bind upwards diffusing P in the oxic sediment layer of the innermost Neva estuary and the areas bioturbated by abundant amphipods. 相似文献
19.
The effect of soil pH on the competitive abilities of twoRhizobium leuminosarum bv.phaseoli type I and one type II strains was examined in a nonsterile soil system.Phaseolus vulgaris seedlings, grown in unlimed (pH 5.2) or limed (pH 7.6) soil, were inoculated with a single-strain inoculum containing 1 × 106 cells mL–1 of one of the three test strains or with a mixed inoculum (1:1, type I vs. type II) containing the type II strain CIAT 899 plus one type I strain (TAL 182 or CIAT 895). At harvest, nodule occupants were determined. In a separate experiment, a mixed suspension (1:1, type I vs. type II) of CIAT 899 paired with either TAL 182 or CIAT 895 was used to inoculateP. vulgaris seedlings grown in sterile, limed or unlimed soil. The numbers of each strain in the rhizosphere were monitored for 10 days following inoculation. The majority of nodules (> 60%) formed on plants grown in acidic soil were occupied by CIAT 899, the type II strain. This pattern of nodule occupancy changed in limed soil. When CIAT 899 was paired with TAL 182, the type I strain formed 78% of the nodules. The number of nodules formed by CIAT 899 and CIAT 895 (56% and 44%, respectively) were not significantly different. The observed patterns of nodule occupancy were not related to the relative numbers or specific growth rates of competing strains in the host rhizosphere prior to nodulation. The results indicate that soil pH can influence which symbiotype ofR. leguminosarum bv.phaseoli will competitively nodulateP. vulgaris. 相似文献
20.
Frederick M. Soster David T. Harvey Michelle R. Troksa Travis Grooms 《Hydrobiologia》1992,248(3):249-258
A laboratory experiment was conducted to determine the effect of tubificid worms on the flux of zinc into lake sediments. Forty-six cores of Lake Erie sediment, with and without (control) tubificid worm populations, were exposed to aquarium water with a zinc concentration of about 5 mg 1–1 for 139 days. Pore water and exchangeable particulate zinc concentrations in the top 12 cm of sediment were periodically determined in pairs of cores — one with worms and one without worms — at 1 cm depth increments. After 139 days, pore water zinc concentrations in sediments with and without worms were nearly identical in the 0–1 cm interval (4.1 and 4.3 mg 1–1 respectively), but were significantly greater in the sediments with worms in the 1–2 cm (4.4 vs. 0.3 mg1–1) and the 2–3 cm (1.3 vs. 0.3 mg 1–1) intervals. Exchangeable particulate zinc concentrations in the 0–1, 1–2, and 2–3 cm intervals in sediments with worms were 612.3, 750.7, and 191.5 µg g–1 dry sediment respectively, whereas in sediments without worms, concentrations were 375.4, 5.9, and 3.2 µg g–1 dry sediment. The increased flux of zinc into tubificid-inhabited sediments was caused by the conveyor belt feeding activity of the worms, which continuously exposed sedimentary particles to the overlying water. Movement of zinc into sediments with worms was dominated by adsorption and by particle movement, whereas movement of zinc into control sediments was by adsorption at the sediment-water interface and diffusion. The increased concentration of zinc in tubificid-inhabited sediments has important implications with respect to the trophic transfer of zinc through the aquatic food chain. 相似文献