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1.
This paper summarizes results from 8 years (1996–2003) of eddy covariance-based ecosystem CO2 exchange measurements at the Borden Forest Research Station (44°19′N, 79°56′W). The site represents a mid-latitude, 100-year-old, mixed deciduous and coniferous forest dominated by red maple, aspen and white pine. The years 1996 and 1997 were relatively cold, had a late spring and received below average photosynthetic photon flux density (PPFD). This contrasts with an early spring, warmer soil and air temperatures during 1998–1999, and with distinctly wet year of 2000 and dry years of 2001–2003. The combination of early spring, warmer air and soil temperature and relatively high level of PPFD was associated with higher net ecosystem productivity (NEP) that peaked during 1999. Photosynthetic capacity was reduced and NEP showed a mid-growing season depression during the dry years of 2001–2003. Annual average ecosystem respiration (R) determined from a light response model was 30% less than R derived from a logistic respiration equation, relating night time CO2 flux and soil temperature. However these independently determined R values were well correlated indicating that the site is unaffected by fetch and spatial heterogeneity problems. Based on the combined 8 years of growing season daytime data, an air temperature of 20–25 °C and a vapor pressure deficit (VPD) of 1.3 kPa were found to be the optimal conditions for CO2 uptake by the canopy. Over the 1996–2003 period, the forest sequestered carbon at an average rate of 140 ± 111 gC m−2 y−1. The corresponding gross ecosystem photosynthesis (GEP) and R over this period were 1116 ± 93 gC m−2 y−1 and 976 ± 68 gC m−2 y−1, respectively. The annual carbon sequestration ranged from 19 gC m−2 in 1996 to 281 gC m−2 in 1999. However, these estimates were sensitive to frictional velocity threshold () used for screening data associated with poor turbulent mixing at night. Increasing from 0.2 m s−1 (based on the inflection point in the nighttime CO2 flux vs. u* relationship) to 0.35 m s−1 (determined using a selection algorithm based on change-point detection) modified the 8-year mean NEP estimate from 140 ± 111 gC m−2 y−1 to 65 ± 120 gC m−2 y−1. Both approaches show that the Borden forest was a low to moderate sink of carbon over the 8-year period.  相似文献   

2.
The northwest European heathland landscape with its characteristic communities of nutrient-poor and acidic soils has a high nature value, because of its locally high biodiversity and the distinct site conditions. In order to conserve and restore the heathlands, numerous rehabilitation projects have been performed, although with varying success. This is partly due to the fact that the key biogeochemical processes distinguishing the various vegetation types within the heathlands are not known in detail.Therefore, we performed a statistical survey on the main communities and their soil characteristics. In addition, we analyzed the data for key factors determining biodiversity in the heathland landscape.Data from previous studies and surveys was used to compile a dataset of 267 vegetation relevés (classified as EUNIS habitat types) with extensive soil measurements (22 parameters). A canonical discriminant analysis revealed that soil acidity explained most of the differences between the habitat types, while soil moisture content and soil fertility were less important. Acidity-related factors as Al3+, Al/Ca-ratio and pH were also strongly correlated to plant diversity in the majority of the habitat types, respectively, the species-rich Nardus grasslands, the Rhynchosporion communities and the species-rich Molinia meadows. In the dry heaths and over the total heathland landscape, plant diversity was negatively correlated with soil -concentrations. Only in wet heath, nutrient availability, in this case P, was the primary factor in explaining plant diversity.This study presents ranges for all major soil parameters for the studied well-developed heathland habitat types, thereby providing clear guidelines for conservation and restoration.  相似文献   

3.
Rainfall interception losses from an agroforestry system in semi-arid Kenya comprising Grevillea robusta and maize were measured over a period of 33 months. These measurements showed that interception was slightly higher (10.2%) under trees with no maize understorey, than in the intercropped treatment (9.8%), and was directly related to the degree of tree canopy cover. Interception estimates using the reformulated version of the Gash analytical model were 4% lower than measured totals, and were strongly dependent on both canopy cover and on monthly variations in the mean rainfall rate ( , mm h−1).  相似文献   

4.
Collembolan communities were studied in 41 microhabitats in beech and spruce forests of south ( ofín and umava) and central (Jevany) Bohemia. The communities of Collembola were analysed using TWINSPAN and CANOCO programs. The aim of this study was to establish differences between patch (microhatitat) communities and the main forest community in spruce and beech forests, the differences between both types of forests and among different regions of Bohemia. Further questions were: is there a difference in microhabitat communities during secondary forest succession? do some species live exclusively in one or few microhabitats? and does microhabitat diversity influence the biodiversity in forest soils? Material comprising  25 590 specimens of Collembola belonging to 142 species was analysed. Highly significant differences were determined between microhabitat communities in beech and spruce forests, as well as among forests in different regions of Bohemia. Significant differences were also found among microhabitats in forests of different ages. Also, some microhabitat communities of Collembola, e.g. moss on boulders, were significantly different from their main forest community. Certain collembolan species existed exclusively in one or two microhabitats. Patches therefore influenced substantially biodiversity in these forest soils.  相似文献   

5.
To study the effects of earthworm casting on organic matter dynamics, control soil and casts were added as a surface layer (Horizon I) to perspex cylinders containing a ‘base’ soil depleted in organic C (Horizon II). Three treatments with different Horizon I were used; a control containing uningested soil and oak litter (Quercus petraea (Mattuschka) Lieblein), cast derived from the same substrates, and a third (Ew+cast) where cast as well as endogeic (Aporrectodea caliginosa Savigny, Allolobophora chlorotica Savigny) and anecic (Lumbricus terrestris L.) earthworms were included. These were monitored over a 2 year period. Moisture fluctuations were reduced and higher amounts of organic matter and C were present in Horizon I with the cast treatment after 2 years. In addition, the proportion of clay C (and to a lesser extent light fraction) in Horizon I decreased significantly in the control and cast treatments while there was a corresponding increase in the proportions of silt C. Overall, earthworm activity had a limited effect on C distribution in the particle size fractions studied, though the dynamics of organic matter/particle associations may require more than 2 years before clear patterns emerge.  相似文献   

6.
Combined oxygen (O) and nitrogen (N) stable isotope analyses are commonly used in the source determination of nitrate . The source and fate of are studied based on distinct O and N isotopic signatures (δ18O and δ15N) of various sources and isotopic effects during transformation processes, which differ between sources like fertilizer, atmospheric deposition, and microbial production (nitrification). Isotopic fractionation during production and consumption of further affects the δ18O and δ15N signal. Regarding the δ18O in particular, biochemical O exchange between O from and H2O is implicitly assumed not to affect the δ18O signature of . This study aimed to test this assumption in soil-based systems. In a short (24 h) incubation experiment, soils were treated with artificially 18O and 15N enriched . Production of from nitrification during the incubation would affect both the 18O and the 15N enrichment. Oxygen exchange could therefore be studied by examining the change in 18O relative to the 15N. In two out of the three soils, we found that the imposed 18O enrichment of the declined relatively more than the imposed enrichment. This implies that O exchange indeed affected the O isotopic signature of , which has important implications for source determination studies. We suggest that O exchange between and H2O should be taken into consideration when interpreting the O isotopic signature to study the origin and fate of in ecosystems.  相似文献   

7.
Here we offer the first assessment of conditions conducive to dissimilatory nitrate reduction to ammonium (DNRA) in temperate arable soils, through an examination of the potential for this process to occur in a range of soils of contrasting characteristics. NH415NO3 (6.2 g N m−2, 25 atom % excess 15N) was applied, and recovery of 15N in the pool taken as indicative of occurrence of DNRA. Up to 5% of applied 15N was recovered in the pool 2 d after addition of N, glucose (44.6 g C m−2) and l-cysteine (7.7 g m−2, 0.9 g N m−2, 2.3 g C m−2). concentrations were positively correlated with soil pH, ratio, bulk density, sand content and concentration, but negatively correlated with soil C and organic N content. Our results demonstrate the potential for DNRA to contribute to N cycling in temperate arable soils, but its detection and significance is likely to depend on the provision of a low molecular weight C source.  相似文献   

8.
Rapid development and urbanization in the South Carolina (SC) coastal plain may introduce significant nutrients to adjacent tidal creeks and salt marsh estuaries, and threaten estuarine water quality. Microbial denitrification in estuarine soils plays an important role in removing excessive nitrate in coastal waters. Relative contributions of denitrification and ammonium production during nitrate reduction via dissimilatory nitrate reduction to ammonium (DNRA) and soil mineralization determine whether N is lost from the system or retained as ammonium . The objectives of this study were to compare background, short-term and long-term potential denitrification ( and glucose added) rates, and production during microbial conversion in a developing marsh estuary, SC (USA). Denitrification rates were measured using the acetylene block technique in an undeveloped fresh water site (T1W), an undeveloped Spartina marsh (Grave's Dock, GD), and a Spartina marsh at a golf course resort (Chechessee marsh, C3M). Background denitrification with no added was primarily controlled by concentration in soils and surface water. Adding glucose did not enhance either short-term or long-term potential denitrification rates in GD marsh soils. production during microbial removal was significant at both marsh sites, and N-mass balance based on N2O and production suggested a significant contribution of from sources other than DNRA. DNRA was estimated to account for approximately 16.3% and 0% of total added removal in GD surface (0-10 cm) and subsurface (30-40 cm) soils, and 1.9 and 23.2% in C3M surface and subsurface soils. Excessive generation from processes other than DNRA may be attributed to stimulated mineralization, and this stimulation was estimated to enhance soil ammonification by 0.5∼4 times compared to background generation with no added. Our results suggest that although the marsh soils displayed high potential of removal via denitrification, the produced via a combination of DNRA and enhanced mineralization may allow to accumulate and be transported to coastal waters.  相似文献   

9.
Although it remains unclear why NH3-oxidizing bacteria (AOB) of the genus Nitrosospira dominate soil environments, and why Nitrosomonas spp. are less common, virtually no studies have compared their behavior in soil. In this study, the NH3 oxidation rates of Nitrosomonas europaea (ATCC 19718) and Nitrosospira sp. AV were compared in three differently textured soils containing a range of extractable contents (2-11 μg soil). Soils were adjusted to pH 7.0-7.4 with CaCO3 and sterilized with γ-radiation. Cell suspensions of each bacterium were inoculated into the soils to bring them to two-third of water-holding capacity and cell densities ∼2.5×106 g−1 soil. In virtually all cases, rates of production for both N. europaea and Nitrosospira sp. AV were linear over 48 h, and represented between 13 and 75%, respectively, of the maximum rates achieved in soil-free bacterial suspensions. Soil solution concentrations that supported these rates ranged between 0.2 and 1.5 mM. Addition of 21-36 μg soil raised soil solution levels to 1.8-2.5 mM and stimulated production to a greater extent in N. europaea (3.3-6.6-fold) than in Nitrosospira sp. AV (1-2.1-fold). Maximum rates of production were obtained by raising soil solution levels to 3-4 mM with a supplement of ∼80-90 μg soil. Ks values in soil for Nitrosospira sp. AV and N. europaea were estimated as 0.14 and 1.9 mM , respectively, and estimates of Vmax were about 3.5-times higher for N. europaea (0.007 pmol h−1 cell−1) than for Nitrosospira sp. AV (0.002 pmol h−1 cell−1). The cell density of N. europaea increased in sterile Steiwer soil independent of supplemental . In the case of treatments receiving supplemental , growth yields of N. europaea calculated from either produced or consumed were similar to those reported in literature (3.5×106-6×106 cells μmol−1). A higher growth yield was measured in the case of zero added (2.7×107 cells μmol−1), indicating that use of organic carbon compounds might have occurred and resulted in some energy sparing. Our results suggest that Nitrosospira spp. with a Ks similar to Nitrosospira sp. AV may have an advantage for survival in soil environments where soil solution levels are less than 1 mM. However, it is apparent that AOB like N. europaea are poised to take advantages of modest increases in extractable that raise soil solution levels to about 2.0-2.5 mM.  相似文献   

10.
W.D. Nettleton  M.D. Mays 《CATENA》2007,69(3):220-229
There is much interest in predicting future carbon-soil degradation and that occurring today. We have National Soil Survey Laboratory data to assess some of the soil carbon degradation in the Great Basin and western Utah. For this we included data on 32 Nevada and Utah soils on Pleistocene geomorphic surfaces at elevations of 973 to 3172 m. Their mean annual precipitation (MAP) ranges from 20 to 55 cm and mean annual soil temperatures (MAST) from 5 to 12 °C. The MAP and MAST closely correlate with elevation (E) (r = 0.96 and − 0.97 respectively). Mountain big sagebrush (Artemisia tridentata Nutt. ssp. vaseyana (Rydb.) Beetle) dominates vegetation at the higher, colder elevations. Wyoming big sagebrush (Artemisia tridentata Nutt. ssp. wyomingensis Beetle and Young) and juniper (Juniperus L.) dominate at intermediate elevations. Little sagebrush (Artemisia arbuscula Nutt.) and related desert species dominate at the lower, warmer elevations. We used acid dichromate digestion and FeSO4 titration to analyze for soil organic carbon (SOC) and bulk density and coarse fragments in the soils to put the data on a volume basis. The soils are well drained and uncultivated. Accumulation of organic carbon in each pedon (OCp) is correlated to MAP and MAST (r = 0.81, and − 0.78 respectively). We predicted OCp from the relationship,
(1)
r2 = 0.64, S.E. = 1.30, n = 32. The soil OC degradation that may have occurred through the Holocene ranges from 35% at sites of the present Aridisols and Vertisols to 22% for the sites of the Mollisols and Alfisols. Eq. (1) shows that today, MAST rises of 1 to 3 °C would produce further OCp degradation from today's levels of 1% to 13% in Aridisols and Vertisols and 12% to 25% in the Mollisols and Alfisols respectively. It also shows that if the MAST drop of 6 °C predicted for the Pleistocene occurred, many of the Aridisols and Vertisols likely would have been Mollisols or Alfisols during the Pleistocene. A temperature rise of 1 °C in a century would likely move the Mollisol–Aridisol boundary from its present 2300 m elevation to an elevation of about 2900 m. A temperature rise of 3 °C in a century would likely move the Mollisol–Aridisol boundary from its present 2300 m elevation to elevations of the highest elevations in Nevada and to the middle of Idaho. Increasing the temperature by 3 °C will likely also increase the area affected by severe desertification in the southern Great Basin north by about 20%.  相似文献   

11.
Organic matter dynamics and nutrient availability in saline alkaline soil of the former lake Texcoco will determine the success of a planned reforestation program. Uniformly labelled 14C-maize (MAI-treatment) and glucose (GLU-treatment) with or without 200 mg  kg−1 soil (MAI-N treatment and GLU-N treatment, respectively) were added to soils with electrolytic conductivity (EC) 56 dS m−1 (soil A) and 12 dS m−1 (soil B) to investigate the importance of N availability on decomposition of organic material. Production of CO2 and and inorganic N dynamics were monitored. The amount of 14C-glucose mineralized increased 1.8-times in the soil A, but had no effect in the soil B when 200 mg  kg−1 soil was added, while the amount of 14C-maize mineralized increased 1.7 and 1.3-times when 200  kg−1 soil was added in the soils A and B, respectively. Application of increased priming effect 3.7-times in the MAI-treatment of the soil A and 3.4-times in the GLU-treatment, while in the soil B the increase of priming effect was 4.1-times in the MAI-treatment and 3.7-times in the GLU-treatment. Of the 200 mg  kg−1 added to both soils less than 10 mg NH3-N kg−1 was volatilized within one day, while 22 and 44 mg  kg−1 soil was fixed on the soil matrix in the soil A and the soil B, respectively. Therefore more than 100 mg −N kg−1 was immobilized into the microbial biomass within the first day. Concentration of nitrite increased sharply in all the treatments of soil A at the onset of the incubation followed by a decrease. A similar pattern was observed in the GLU-N and MAI-N treatments of the soil B, but not in the other treatments. A decrease in concentration of was observed in both soils followed by an increase in the MAI-N and GLU-N treatments of the soil B. It was found that application of had a stimulating effect on the decomposition of maize and glucose, and on the priming effect, while assimilatory reduction of resulted in an increase of in the soil A, and nitrification in the soil B.  相似文献   

12.
Our aim was to study whether the in situ natural abundance 15N (δ15N)-values and N concentration of understory plants were correlated with the form and amount of mineral N available in the soil. Also to determine whether such differences were related to earlier demonstrations of differences in biomass increase in the same species exposed to nutrient solutions with both and or to alone. Several studies show that the δ15N of in soil solution generally is isotopically lighter than the δ15N of due to fractionation during nitrification. Hence, it is reasonable to assume that plant species benefiting from in ecosystems without significant leaching or denitrification have lower δ15N-values in their tissues than species growing equally well, or better, on We studied the δ15N of six understory species in oak woodlands in southern Sweden at 12 sites which varied fivefold in potential net N mineralisation rate The species decreased in benefit from in the following order: Geum urbanum, Aegopodium podagraria, Milium effusum, Convallaria majalis, Deschampsia flexuosa and Poa nemoralis. Four or five species demonstrated a negative correlation between and leaf δ15N and a positive correlation between and leaf N concentration. In wide contrast, only D. flexuosa, which grows on soils with little nitrification, showed a positive correlation between and the leaf N concentration and δ15N-value. Furthermore, δ15N of plants from the field and previously obtained indices of hydroponic growth on relative to were closely correlated at the species level. We conclude that δ15N may serve as a comparative index of uptake of among understory species, preferably in combination with other indices of N availability. The use of δ15N needs careful consideration of known restrictions of method, soils and plants.  相似文献   

13.
In exploring the dynamics of iron and nitrogen cycling in sediments from riparian forests we have observed a redox reaction that has not been previously described. During incubations of soil slurries under strictly anaerobic conditions, we repeatedly measured an unexpected production of both nitrite () and ferrous iron [Fe(II)]. Using this indirect evidence we hypothesize that, under anaerobic conditions, there is a biological process that uses ferric iron [Fe(III)] as an electron acceptor while oxidizing ammonium () to for energy production. This oxidation under iron reducing anaerobic conditions is thermodynamically feasible and is potentially a critical component of the N cycle in saturated sediments.  相似文献   

14.
The clear dependence of N2O production through denitrification on available nitrate in soil has been shown in many studies. Since N availability similarly limits the growth of plants, the resource competition with vegetation limits the activity of denitrifying microbes and may consequently moderate the N2O emissions from peatlands. We used uptake by Eriophorum vaginatum L. as a vegetation competition factor for microbes. The species was selected for the experiment because it has high nutrient use efficiency in low-nutrient conditions and high nutrient uptake efficiency in luxuriant nutrient conditions. We measured gaseous N flux as N2O (end product of denitrifier activity) in a restored peatland in central Finland with acetylene inhibition technique over a growing season from sample plots with varying addition levels and E. vaginatum cover. The resource competition effects were analysed with a model that used exponential decay dependence of N2O flux on the leaf area of E. vaginatum, and saturating response of N2O flux to addition level. The model explained the variation in N2O fluxes well (R2=0.86). The model simulation showed that the increasing nutrient uptake of E. vaginatum decreased the N2O fluxes exponentially. Simultaneously, denitrification appeared to saturate even in conditions with high availability of and low level of competition by vegetation. Thus, E. vaginatum is an effective competitor for in sedge-dominated peatlands that controls the availability of for denitrification, and consequently moderates the N2O emissions from peatlands.  相似文献   

15.
The effect of high nitrogen (N) depositions on forest ecosystems is an important concern in North America and may lead to N saturation of forest ecosystems and contribute to soils and surface water acidification. In this study, nitrogen dynamics in the FH layers of a sugar maple (SM), a balsam fir (BF) and a black spruce (BS) forest was characterized using a short term 15N isotopic pool dilutions approach and mid-term FH material incubation both in situ and in the laboratory. The short term dilutions approach indicated that the mean residence times of and in the FH material of the three sites were low (<1 d). The amount of inorganic nitrogen () recycled annually within the exchangeable forest floor reservoir was between one and two orders of magnitude larger than the annual atmospheric N deposition found at each of the sites. The BS site was clearly distinct than the two other forest types in that net N mineralization was negligible, even in absence of root uptake, suggesting that soil microorganisms were severely N limited. While net nitrification was not observed within the FH material of the BF site, did accumulate in the FH of the SM despite a low pH of 3.72 presumably because of heterotrophic nitrification or as a result of acid-tolerant autotrophic nitrification. The difference in N dynamics between the sites were most probably caused by dominant tree species. Transformation rates of inorganic N were higher in SM, followed by BF and BS stands. Given that the potential to mineralize inorganic N matches with a superimposed N atmospheric deposition gradient in Québec, the sugar maple forest is more likely to be affected by N saturation than coniferous forests.  相似文献   

16.
Several authors have reported that nitrification in acid soils may be restricted to microsites having a more favorable pH. The aim of this study was to propose a conceptual model of the functioning of nitrification in hot-spots, and to test it with the experimental data obtained in laboratory conditions using twelve tropical unamended and -amended soils with a wide range of pH (from 4.2 to 6.9). Nitrification was also measured in two selected soils where the pH was adjusted from 3.5 to 6.2. The model characterizes the relationship between the nitrification rates in unamended and -amended soils as a function of pH. It is based upon the assumption that nitrification of the coming from N mineralization occurs in the hot-spot (RNh), and the nitrification of the added occurs in the hot-spot and also in its adjacent surrounding region (RNs). The experimental design was chosen to be able to estimate both nitrification rates. Soil acidity limited nitrification more in -amended soils than in unamended ones. From our approach, this is due to less favorable conditions for nitrification in the region surrounding the hot-spot. The effect of self-induced acidity on nitrification was not noticeable neither in unamended nor in -amended treatments. The model described well three observations made in the experiments: (i) the minimum pH for nitrification to occur was lower for RNh (pH<4.2) than for RNs (pH<4.7), (ii) the RNh/RNs ratio increased with the decrease of pH (from 1.5 at pH 6 to 8.5 at pH 4), and (iii) for a given pH, the RNh/RNs ratio increased with the decrease of the initial pH of the soil. Among the soil parameters determined in this study (i.e. exchangeable Al, EDTA-extractable Cu and Zn, total C and N), only pH was related to nitrification. However, for a given pH, nitrification varied 3-fold among soils, depending upon their initial pH. This suggests that soil pH as determined on bulk soil is not suitable to predict nitrification in each individual soil, because it is not representative of the acidity level within the hot-spot.  相似文献   

17.
The potential impact of timber harvesting in the boreal forest on aquatic ecosystem water quality and productivity depends in part on the production of nutrients within the soil of the harvested catchment. Nitrogen supplied by organic matter decomposition is of particular interest because of the important role that N plays in biotic processes in surface waters, and in forest nutrition in general. Logging slash quality and input to the forest floor has the potential to influence N availability after harvest on clearcut sites. Net production of organic and inorganic-N and microbial biomass C and N concentrations were determined during a 90-day laboratory incubation at constant temperature and moisture. Incubated soils included F horizon and shallow mineral soil horizons (0-5 cm) from unharvested and full-tree harvested (2 and 12 growing seasons since harvest) boreal forest sites at the Esker Lakes Research Area (ELRA), in northeastern Ontario, Canada. In an ancillary experiment, black spruce foliage was added to unharvested forest floor material after 30 days during a 90-day laboratory incubation to simulate the influence of logging slash from full-tree harvesting on C and N dynamics. Twelve-year old clearcut F horizon material released on average 75 and 5 times more -N and 3 and 2 times as much inorganic-N than soil collected from unharvested and 2-year-old clearcuts, respectively. This increase in -N accumulation during the incubation was accompanied by decreases in both exchangeable -N and microbial biomass C and N levels. Net daily changes in microbial biomass N were significantly related to organic and inorganic-N accumulation or loss within the F horizon. Mineral soil release of inorganic-N was lower than release from the forest floor. Nitrate-nitrogen accumulation was lower, and -N accumulation was higher in mineral soil from unharvested sites when compared to 12-year-old clearcuts. Calculated harvest response ratios indicated that incubated mineral soil from the 12-year-old clearcut sites released significantly greater amounts of -N than 2-year-old clearcuts. Incorporation of black spruce needles into F horizon material reduced the production of organic and inorganic-N and increased microbial biomass N. Laboratory incubations of F horizon and shallow mineral soil from 12-year-old clearcuts suggested that these boreal soils have the capacity for increased inorganic-N production compared to uncut stands several years after harvesting. This has the potential to increase N availability to growing boreal forest plantations and increase N leaching due to greater -N levels in the forest soil.  相似文献   

18.
High and low affinity methane oxidation potentials were measured for soils under five fully replicated land-use treatments over an entire calendar year. Simultaneous measurements of soil nitrification potential in replicate soil samples were also made. Both high and low affinity CH4 oxidation were significantly reduced in the nitrate-rich soils under alder, compared to the other four vegetation treatments (oak, Norway spruce, Scots pine and grass). However, the effect of land-use was less for high affinity methanotrophy than for low affinity CH4 oxidation. Nitrification rates were highest in alder soils, with the greatest potential for oxidation occurring in the top 5 cm of the soil. No significant relationship between potential nitrification rate and low affinity CH4 oxidation was seen. However, a significant negative relationship between nitrification and high affinity CH4 oxidation was identified. We found vegetation type to be a key determinant of soil-mediated CH4 and oxidation, but found no evidence for significant CH4 oxidation by nitrifying bacteria.  相似文献   

19.
We studied the effects of varied collembolan numbers on three compensatory mechanisms of nutrient uptake: fine root mass, endomycorrhizal development, and physiological uptake capacity. We grew ash (Fraxinus pennsylvanica) with or without the arbuscular mycorrhizal fungus Glomusintraradices, with 0, 10 or 50 initial Collembola (Folsomia candida). After 83 d root and uptake rates, endomycorrhizal development, and plant biomass were determined. Plant mass increased with Collembola number. Collembola interacted with mycorrhizae in their effects on N uptake and leaf N. Collembola in the absence of mycorrhizal roots were associated with lower N uptake and leaf N at 10 than at 0 or 50 initial Collembola. In contrast, Collembola in the presence of mycorrhizal roots were associated with the highest rate of N uptake and leaf N at 10 versus 0 or 50 initial Collembola. Hence as initial Collembola number increased, the relative importance of root system traits that determined N uptake changed from root physiological uptake capacity, presence of mycorrhizal roots, to fine root biomass.  相似文献   

20.
To study the effects of short-term fluctuation of nitrate concentrations on the nitrate-reducing community, repacked soil cores were amended with 0, 100 and soil and incubated for 3, 7 and 14 days, respectively. The nitrate reductase activity was determined in a laboratory-based enzyme assay. In parallel, the community structure of nitrate-reducing microorganisms was characterised by RFLP-PCR using the functional gene narG, which encodes the catalytic site of the membrane-bound nitrate reductase. The community structure remained constant over the experimental period indicating that this functional community is characterised by a high resistance towards fluctuating nitrate concentrations. Decreases in nitrate concentration as well as increase in pH values indicated a very active nitrate-reducing community under nitrate addition. Surprisingly, inhibition of nitrite reductase by 2,4-dinitrophenol, which is a precondition for the measurement of nitrate reductase activity, could not be achieved in the treatment despite increased concentrations of the inhibitor. However, comparison of the nitrate reductase in the control and the treatment showed a significant increase in the latter at day 3. No further differences were observed at days 7 and 14, which suggests a high resilience of the nitrate reductase activity.  相似文献   

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