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  • 1
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 309 (1984), S. 728-728 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] TROELSTRA ET AL. REPLY—We agree with McCoy and Stanley's view that the age at the bottom of the Tyro Basin core must be considerably younger than we had assumed in our papers, which were mainly based on shipboard observations. Shore-based analyses, still in progress, have produced different data. ...
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  • 2
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The mode of accumulation of organic-rich sediments within the deep marine environment is of great interest in determining the controls of hydrocarbon source rock formation. Modern examples of the formation of these sediments have been encountered in the Black Sea, the California Borderland basins, ...
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 76 (1988), S. 313-320 
    ISSN: 1432-1939
    Keywords: Ammophila arenaria ; Calammophila baltica ; Sand dunes ; Soil sterilization ; Soil pathogens
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary To study the origin of replant disease of Ammophila arenaria (L.) Link the growth and development in sand originating from the rhizosphere of a natural Ammophila vegetation was compared with the growth in sand from the sea-floor. In a greenhouse experiment, the growth of Ammophila seedlings in rhizosphere sand, when compared with that in sea sand, was significantly reduced. As sterilization by means of gamma-irradiation increased the biomass production of Ammophila seedlings significantly, it was concluded that the rhizosphere sand contained biotic factors that were harmful to Ammophila. In rhizosphere sand the roots of Ammophila were brown and poorly developed, and the specific uptake rates of N, P and K were reduced. The shoot weight proportion of the total plant dry matter was hardly influenced. In an outdoor experiment with Ammophila seedlings and cuttings, using both sands, the mortality was high and the plants were feeble in rhizosphere sand whereas plants in sea sand grew vigorously. It seems plausible that the plants in rhizophere sand were dessicated because the root system was shallow and badly developed. In the greenhouse experiments, Ammophila cuttings were less sensitive to the inhibiting factors in the rhizosphere than seedlings. This was confirmed in the outdoor experiment. Calammophila baltica (Fluegge ex Schrader) Brand, however, was hardly affected by the harmful biotic factors in the greenhouse. These results are discussed with reference to the ecology of Ammophila. It is assumed that the catching of fresh windblown sand provides Ammophila with a way to escape from harmful biotic soil factors, and it was concluded that degeneration of Ammophila is caused mainly by self-intolerance due to these biotic soil factors.
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  • 4
    ISSN: 1432-0789
    Keywords: Lime ; Forest soil ; Nitrification ; N mineralization ; Nitrate leaching ; Pinus sylvestris ; Pseudotsuga menziesii ; Quercus robur
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The effect of liming on in-situ N transformations was studied in two stands of different ages of each of Scots pine (Pinus sylvestris L.), Douglas fir [Pseudotsuga menziesii (Mirb.) Franco], and common oak (Quercus robur L.). The stands were located on acid sandy soils in an area with high atmospheric N input. The organic matter of the upper 10-cm layer of the soil, including the forest floor, had a relatively high N content (C: N ratio 〈25) in all stands. Using a sequential core technique, N transformations were measured in both control plots and plots that had been limed 3 years previously with 3 t ha-1 of dolomitic lime. Limed plots had a higher net NO inf3 sup- production and a higher potential for NO inf3 sup- leaching than the controls in all stands except that of the younger oak. Net N mineralization did not differ significantly between limed and control plots in oak stands and younger coniferous stands but was significantly lower in the limed plots of the older coniferous stands. It is concluded that long-term measurements of net N mineralization in limed forest soils are needed to evaluate the effect of liming with respect to the risk of groundwater pollution.
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  • 5
    ISSN: 1573-5036
    Keywords: ambient concentration ; exponential nutrient-addition ; nitrate compensation point ; nitrate uptake ; Plantago lanceolata
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Some water-culture experiments were carried out to measure the ambient nitrate concentration under conditions of exponential addition of nitrate. Juvenile plants ofPlantago lanceolata were therefore grown on an agitated nutrient solution. Nitrate was continually added to the culture vessels during the experimental period. The amount added per plant increased exponentially with time, in accordance with the formula: $$NO_3 - N = N_0 .(e^{(RAR.t)} - 1)$$ (N0=initial content of N in the seedling, RAR=relative addition rate, t=time in days). There were three treatments corresponding to RAR's of 0.20, 0.15 and 0.10 d−1. All of them were suboptimal forP. lanceolata. Nitrate concentrations of the culture solution were measured weekly. In all cases plants were in steady state after two weeks. The relative growth rate was about equal to the RAR within treatments. The root weight ratio was inversely proportional to the RAR, and the internal N concentration proportional. Ambient nitrate concentrations were relatively high during the first two weeks. Ambient concentrations in the second half of the culture periods ranged from 0.35 to 1.8 μM. Linear and multiple regressions of the external nitrate concentration on the specific absorption rate (SAR), and on SAR and some other variables, respectively, were carried out. Most of its variation could be explained by the SAR (r2=0.9827); root size had a minor effect. The experimental results lead to the conclusion that ambient concentrations in culture experiments with exponential nutrient-addition are a result of the treatment. They also indicate which external concentrations may be expected to create strongly suppressed growth. Furthermore, the experiments suggest that the lower limit for nitrate absorption is a zero concentration.
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  • 6
    ISSN: 1573-5036
    Keywords: acid-tolerantversus acid-sensitive ; chemolithotrophic nitrification ; heathland humus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The nature of nitrification in the organic horizons (FH) of two heathland soils was studied. Two types of chemolithotrophic nitrification but no heterotrophic nitrification were detected in the acid heathland humus. One type was predominant in slow nitrate producing humus. It was acid-sensitive but could be stimulated by urea at low pH. The other type was acid-tolerant, it was not stimulated by urea. The latter type was predominant in fast nitrate producing humus. The occurrence of acid-tolerant chemolithotrophic nitrification provides indirect evidence for the existence of previously unknown acid-tolerant, chemolithotrophic, ammonium-oxidizing bacteria. Nitrification by these micro-organisms may be an important source of soil acidification in acid soils that are exposed to high levels of ammonium deposition.
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  • 7
    ISSN: 1573-5036
    Keywords: ammonium ; labile organic P ; nitrate ; N mineralization ; phosphorus ; Plantago major L. ssp. pleiosperma ; soil nutrient availability ; soil nutrient pools ; spatial variation ; temporal variation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract As part of a research project on the variation in life-history characteristics within a population of Plantago major L. ssp. pleiosperma, seasonal and spatial variability in the availability of macronutrients (N, P, and K) were examined on a small scale in the 0–25 cm soil depth at a primary beach plain site, embanked since 1966. On the basis of distinct differences, among other things, in plant biomass, an a priori division into three different types of microhabitat occurring in a mosaic distribution pattern was made: an overall low-lying area (subsite 1) with slightly elevated patches of 0.5 to 1.5 m in diameter (subsite 2) and rather large patches, 20 to 40 m in diameter, of sea buckthorn shrubs, with small and relatively open spots (subsite 3) in the transitional zone from lower area into scrub. All three subsite types were studied within a total area of approximately 2000 m2. Three methods of analysis were applied: an inventory survey (sampling once at the start of the growing season), an analysis of the seasonal variation (sampling at approximately monthly intervals during the period April-November), and an assessment of nitrogen mineralization potentials in the laboratory (sampling once at the beginning of the growing season). All three procedures clearly demonstrated the occurrence of differences in the availability of nutrients over very short distances, i.e. a pronounced spatial variability among subsites. Particularly the availability of N and P appeared to have increased at the subsites 2 and 3, when compared to subsite 1. This small-scale differentiation in soil properties has occurred in an essentially homogeneous parent material (e.g. in texture and carbonate content) over a period of about 20 years. Besides a spatial variability, statistically significant temporal fluctuations were observed in the availability of N, P, and K. Relative fluctuations of mineral N (as indicated by the range/mean ratio) were especially large at the subsites 2 and 3.
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  • 8
    ISSN: 1573-5036
    Keywords: ammonium ; Hippophaë rhamnoides ; hydroxyl-ion efflux ; ionic balance ; ion uptake ; nitrogen fixation ; nitrate ; nitrate reductase activity ; proton efflux ; rhizosphere pH
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Growth of 2-month-old nonnodulatedHippophaë rhamnoides seedlings supplied with combined N was compared with that of nodulated seedlings grown on zero N. Plant growth was significantly better with combined N than with N2 fixation and, although not statistically significant for individual harvests, tended to be highest in the presence of NH 4 + , a mixture of NH 4 + and NO 3 − producing the highest yields. Growth was severely reduced when solely dependent on N2 fixation and, unlike the combined-N plants, shoot to root ratios had only slightly increased after an initial decrease. An apparently insufficient nodule mass (nodule weight ratio 〈5 per cent) during the greater part of the experimental period is suggested as the main cause of the growth reduction in N2-fixing plants. Thein vivo nitrate reductase activity (NRA) of NO 3 − dependent plants was almost entirely located in the roots. However, when grown with a combination of NO 3 − and NH 4 + , root NRA was decreased by approximately 85 per cent.H. rhamnoides demonstrated in the mixed supply a strong preference for uptake of N as NH 4 + , NO 3 − contributing only for approximately 20 per cent to the total N assimilation. Specific rates of N acquisition and ion uptake were generally highest in NO 3 − +NH 4 + plants. The generation of organic anions per unit total plant dry weight was approximately 40 per cent less in the NH 4 + plants than in the NO 3 − plants. Measured extrusions of H+ or OH− (HCO 3 − ) were generally in good agreement with calculated values on the basis of plant composition, and the acidity generated with N2 fixation amounted to 0.45–0.55 meq H+. (mmol Norg)−1. Without acidity control and in the presence of NH 4 + , specific rates of ion uptake and carboxylate generation were strongly depressed and growth was reduced by 30–35 per cent. Growth of nonnodulatedH. rhamnoides plants ceased at the lower pH limit of 3.1–3.2 and deterioration set in; in the case of N2-fixing plants the nutrient solution pH stabilized at a value of 3.8–3.9 without any apparent adverse effects upon plant performance. The chemical composition of experimental and field-growing plants is being compared and some comments are made on the nitrogen supply characteristics of their natural sites.
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  • 9
    ISSN: 1573-5036
    Keywords: acidic soils ; ammonium ; Deschampsia flexuosa (L.) Trin. ; nitrate ; nitrification ; N-mineralization ; NRA ; seasonal variation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Two Dutch heathland sites Hoorneboeg (HB) and Ede, dominated by Deschampsia flexuosa and differing in nitrate production, were sampled for an entire growing season. A large number of soil and plant parameters were monitored in an attempt to assess the contribution of nitrate in the N supply and its assimilation by Deschampsia. Average NO3 − and NH4 + concentrations (mg kg−1) in the top 10-cm depth were 0.03 and 2.2, respectively, for HB, and 2.1 and 6.7, respectively, for Ede. Laboratory incubations of intact cores and experiments with FH-layer suspensions showed significantly higher mineralization and nitrification rates for the Ede site during most of the season. Nitrification was largely controlled by the rate of net N-mineralization, which in turn was highly affected by soil moisture. Nitrate production was virtually zero at HB and accounted for 25% of the net N-mineralization at Ede. Shoot chemical composition showed no essential differences for the two sites, but mean in vivo (current) foliar NRA was almost 2-fold higher at Ede than at HB, indicating some utilization of nitrate at the former location. At the HB site with essentially no nitrate production, however, enzyme activities were clearly higher than ‘basal’ constitutive levels in NH4 +-fed plants. Apparently, shoot NRA at the HB site became positively affected by factors other than nitrate availability and/or showed disproportional increases in response to atmospheric nitrate inputs. Root NRA displayed the same low basal level at the two sites. Nitrate fertilization (100 kg N ha−1) yielded maximally induced foliar NRAs similar to levels found in hydroponic nitrate plants. Although no accumulation of free NO3 − was observed in shoots from fertilized plots, increases in foliar concentrations of both organic N and carboxylates clearly indicated nitrate assimilation. Root NRA showed no response to nitrate addition. It is concluded that current NRA measurements in Deschampsia at heathland sites are of limited value only, especially when interpreted ‘in isolation’. A combined approach, using concurrently conducted soil and plant analyses, will allow the extent of nitrate utilization in the field to be best characterized.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Plant and soil 127 (1990), S. 193-200 
    ISSN: 1573-5036
    Keywords: acetylene ; heathland ; humus ; nitrification patterns ; pH ; urea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Some characteristics of nitrification in 41 humus samples of Dutch heathlands were studied. Most of the acid humus samples (30) showed accumulation of nitrate during a 4-week incubation of field-moist material. In these samples net nitrate production was completely blocked by 0.06% acetylene indicating that nitrification was probably of a chemolithotrophic nature. From a comparison of the net production of nitrate in humus suspensions at pH 4 and pH 6 a differentiation into four patterns could be made: I. No nitrate production at either pH value studied (12 samples) II. Acid-sensitive nitrate production (3 samples) III. Acid-tolerant, pH-dependent nitrate production (10 samples) IV. Acid-tolerant, pH-independent nitrate production (16 samples) The results show that acid-tolerant, chemolithotrophic nitrification is widespread among Dutch heathland soils. Absence of potential net nitrate production in humus samples is most likely caused by limitations in the supply of ammonium or oxygen.
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