bluuebunny/crossref_metadata_2025_split huggingface dataset:
Interaction between Heracleum laciniatum and some other plants
Authors: Myrås Harald , Junttila Olavi 
Published: July 2006

The aim of this study was to find out whether the low plant production under a canopy of Heracleum laciniatum Horn was due to competition for water, nutrients or light or to chemical inhibitors produced by H. laciniatum.The main conclusion is that the low plant production observed under the canopy is due to competition for light. There were also indications that the competition for nutrition was larger in the soil under H. laciniatum than in the meadow outside the stand, but it has not been shown that nutrient supply limits the plant growth under the canopy. There were no indications that competition for water was a limiting factor. Water percolated through pots with H. laciniatum plants slightly inhibited growth of Poa pratensis and Phleum pratense, but had no effect on H. laciniatum. In soil samples collected from mid of June to late October seeds of Phleum pratense germinated better in meadow‐soil than in soil collected under H. laciniatum. Allelopathy is suggested to account for a minor part only of the suppressed plant production under a H. laciniatum canopy.
Oxygen and nitrate respiration in a reed swamp sediment from a eutrophic lake
Authors: Andersen Frede Østergaard 
Published: July 2006

Seasonal measurements of the oxygen and nitrate uptake by a reed swamp sediment were carried out in a shallow, eutrophic Danish lake, Arreskov Sø. The oxidation of organic carbon in the sediment by aerobic and nitrate respiration was 290 and 188 g C m−2 yr−1 respectively. During winter, nitrate respiration amounted to 94% of the total carbon oxidation, whereas it was zero during summer. On an annual basis nitrate respiration constituted 39% of total respiration. Sediment nitrate uptake was correlated to nitrate concentration. In consequence of this the nitrate uptake rates varied during the year from zero in summer to 55 mg N m−2 d−1 in spring.Oxygen uptake rates varied from 30 to 250 mg O2 m−2 h−1 during the year, with a maximum uptake in August. The oxygen uptake per year was calculated to 860 g O2 m−2. The oxygen uptake rate was correlated to lake temperature and Kjeldahl nitrogen content of the sediment. The oxygen uptake rate, however, showed no correlation with loss on ignition of the sediment. A Q10‐value of 2.2 was found for lake measurements in the temperature interval of 5–15°C. The corresponding O10‐value in the laboratory was 2.6. A high microbial biomass indicated by the maximum content of Kjeldahl nitrogen and the lowest ratio of loss on ignition on Kjeldahl nitrogen appeared in late August, when the maximum oxygen uptake occurred. The oxygen uptake rate increased during the time interval from sampling to the start of the experiments.
Comparative primary productivity of algal epiphytes on three species of macrophyte in the littoral zone of Lake Ohrid, Yugoslavia
Authors: Allen Harold L. , Ocevski Boris T. 
Published: July 2006

Primary productivity of algal epiphytes on the surfaces of Phragmites, Potamogeton, and Nuphar was measured seasonally from June 1978, through June 1979, in the littoral zone of Lake Ohrid, using 14C methodology. Surface areas of individual macrophytes were determined throughout the study period through the use of a non‐miscible surfactant and a calibration curve of surfactant weight versus known, calculated surface areas.Mean total surface area available for epiphytic colonization during the study period was 1.032 m2 macrophyte surface per m2 of littoral zone for Phragmites, 0.810 m2 for Potamogeton, and 0.167 m2 for Nuphar. Seasonal rates of mean primary productivity of algal epiphytes on Phragmites from the surface to the light‐compensation depth ranged from 84–1406 mg C m−2 littoral zone d−1; ranges for epiphytes on Potamogeton and Nuphar were 77–586 and 69–268 mg C m−2 littoral zone d−1, respectively. Maximum rates were observed typically during June; minimum rates were observed typically during August to December. Mean daily productivity rates over the 12 month period were for epiphytes on Potamogeton 167.0, on Nuphar 100.4 and on Phragmites 671.2 mg C m−2 littoral zone d−1. Calculated annual production for epiphytes on Nuphar was 36.65, on Potamogeton 60.95 and on Phragmites 245.0 g C m−2 littoral zone yr−1. Epiphytic production data were typically considerably higher than production data obtained for littoral and pelagial planktonic algae and compare favorably with published data for epiphytic and periphytic production in Lawrence Lake, Marion Lake, and Borax Lake.
Dynamics of ectomycorrhizae in Abies amabilis stands: The role of Cenococcum graniforme
Authors: Vogt Kristiina A. , Edmunds Robert L. , Grier Charles C. 
Published: July 2006

The growth and development of the predominant mycorrhizal fungus infecting the root systems of subalpine Pacific silver fir was examined seasonally in 23 and 180 yr old stands. All data was obtained by sorting roots from intact soil cores separated into forest floor and mineral soil horizons.The predominant mycorrhizal fungus infecting the root systems of 23 and 180 yr old Pacific silver fir was Cenococcum graniforme. C. graniforme comprised 36–97% and 40–96% of the total mycorrhizal root tips in the soil profile in the young and old stands, respectively. C. graniforme root biomass reached a maximum in autumn in the young stand, and in winter in the old. Dual mycorrhizal associations were commonly observed on the same root tip during the spring and autumn periods of root elongation in both stands. Over 80% of the C. graniforme roots were located in the forest floor and A‐horizon throughout the study in both stands, Sclerotia were predominantly located in the A‐horizon (38‐70%) in both stands.
Spatial differentiation of ectoparasites on small mammals
Authors: Nilsson Anders 
Published: July 2006

Different ectoparasitic species occur on different areas on the small mammal host: chiggers in the ear muzzle, ticks on the ears and other parts of the head, fleas and lice on the back and most gamasid mites on the posterior part of the host body.The distribution might be affected by (1) the mechanical interference of the host. Thus attached species such as ticks and chiggers occur in areas where direct predation is limited and small and/or very mobile species are found on other parts of the body. (2) interaction between parasitic species. In areas where species meet, there might be a segregation in time or in space. Species such as Laelaps agilis (C. L. Koch) and Haemogamasus nidi Michael are most frequently found within a restricted area on the host, but differ in their seasonal occurrence. In other combinations of species, such as in fleas, there are marked differentiations in body areas used. These differentiations may be evolutionary fixed or manifested at first when species meet. (3) Abundance, where an increasing abundance enlarge the habitat used.
Litterfall in two Canadian deciduous woods: quality, quantity and timing
Authors: Merriam Gray , Dwyer Lianne , Wegner John 
Published: July 2006

Litterfall in two deciduous woods in Ontario, Canada, was caught in bag traps and by new screen traps for two years. The beech‐maple wood produced 818 g m−2 (8.2 t ha−1) and the poplar wood produced only 450 g m−2 (4.5 t ha−1). Of these totals, canopy leaves alone made up 386 g m−2 for the beech‐maple wood and 270 g m−2 for the poplar wood leaving 47% and 34%, espectively, for other litter components. Data are presented for seven types of litter in addition to canopy leaves.Redistribution of litter on the ground causes spatial heterogeneity of substrate and of habitats for decomposers and hence of decomposition.Temporal distributions of various types of litterfall differ between the two woods in relation to their vegetation structure. The diversity of litter types combines with extensive temporal distribution of litterfall in the beech‐maple woodland to give that wood the potential for nearly continuous decomposition activity. In contrast, the poplar woodland has low diversity of litter and short duration of litterfall.
Inputs and transformation of allochthonous particulate organic matter in a headwater stream
Authors: Iversen Torben Moth , Thorup Jens , Skriver Jens 
Published: July 2006

Inputs and outputs of allochthonous particulate organic matter were measured during 15 months in the upper part of a beech forest headwater stream. Inputs were estimated to 716 g m−2 yr−1, and leaves made up 71%. Outputs were estimated to 535 g m−2 yr−1 and consisted mainly of FPOM (92%). Therefore, a significant transformation of CPOM into FPOM took place. The mean FPOM concentration varied between 0.6 and 3.4 mg 1−1, but the daily variations greatly surpassed the seasonal variations. As discharge was rather constant, the observed variations were due to external disturbances, especially precipitation.A tentative scheme for leaf processing is established from the present data and previous studies in the area, indicating that a significant part takes place in the MPOM pool and that microbial and invertebrate processing make up about 50% each of total intra‐system processing.
Nitrogen fixation by free‐living microorganisms in the soil of a mature oak‐stand in Uppland, Sweden
Authors: Nohrstedt Hans‐Örjan 
Published: July 2006

The nitrogenase activity of free‐living microorganisms was investigated in a brown forest soil beneath a mature oak‐Stand outside Uppsala, Central Sweden. The effect of season, air temperature, soil depth and some soil parameters on nitrogenase activity was studied.Only heterotrophic nitrogenase activity was detected. The main activity occurred in the upper 5 cm of the soil profile. The amount of nitrogen fixed during the growth season was calculated to 0.73 kg ha−1. There was a strong seasonal variation of the nitrogenase activity with the highest level in July, August and September. The activity, when the soil was incubated at 25°C, was significantly correlated with the mean air temperature at the field site.
Regeneration of Scots pine Pinus sylvestris at a natural tree‐line in the Cairngorm Mountains, Scotland
Authors: Miller G. R. , Cummins R. P. 
Published: July 2006

The age, density, distribution and reproductive capacity of Scots pine Pinus sylvestris L. were investigated along an altitudinal gradient through the only undisturbed tree‐line remaining in the Cairngorm Mountains. Saplings at 300–410 m a.s.l. were unlikely to develop to reproductive maturity because of repeated browsing by red deer Cervus elaphus L. By contrast, pines were regenerating successfully in scrub at 531–590 m, where the population included individuals of all ages up to 300 yr. Above 590 m, there grew only saplings aged less than 30 yr and these declined in density with increasing altitude up to 730 m.The climate at 531–590 m was not so severe as to prevent pines from growing to reproductive maturity. However, it may have been severe enough to restrict the activities of large herbivores and so the pine saplings there escaped the heavy browsing suffered by plants at lower altitude. Presumably zones of successfully regenerating pine scrub might occur more widely in the Cairngorms but for a shortage of seed‐bearing trees.
Seasonal changes in census efficiency of birds at marshes and fen mires in southern Sweden
Authors: Nilsson Sven G. 
Published: July 2006

Sixteen fens and marshes with areas between 10 and 285 ha was censused at least six times in the period 11 April to 10 June. The proportion of the number of resident species observed on a visit increased from the beginning of the census period up to the end of May. Thereafter it decreased. Variability in the census of the number of species was lowest in the end of May and the beginning of June. Throughout the seasons studied there were frequent visits of non‐resident species. The proportion of non‐resident, but not the proportion of resident species, observed on a visit, increased as the number of resident species at a locality increased.Census efficiencies per ten‐day periods are given for 14 species. Census efficiency of a species correlated positively with the body weight of the species. The highest census efficiency for most species occurred in the period 21 April to 31 May. It is suggested that if two visits are made in that period about 80% (S.D. = 9.8) of the resident species will be observed.
Effects of freshwater outflows on microbial populations in the Tvärminne archipelago, southern Finland
Authors: Väätänen Pentti 
Published: July 2006

The effects of freshwater outflows were evaluated in three ways: (1) microbial populations in the outflow area (mainly Tvärminne Storfjärd) were compared with populations outside the area, (2) direct counts were made at three sites to monitor the abundance of bacteria along the seaward course of the outflows, and (3) a survey was made of the distribution of microorganisms in the archipelago. The indices used for the presence of freshwater outflows in the archipelago were low salinity, increased amounts of humic matter, and increased temperatures in the winter.In the outer archipelago, the effects of the outflows were most evident in the low‐salinity surface layer below the ice and were also distinguishable in spring and late autumn, but were noted only sporadically in the summer. The outflows were traced as far seaward as the border of the sea zone. The outflows transported various types of bacteria, bacterial spores and yeasts, but did not significantly affect the community respiration. Many of the microorganisms flowing with the fresh water in the winter evidently originated from sewage. During the other seasons, the roles of outflows from the firth of Pojoviken and runoff from the land became evident, but their contributions could not be estimated because fresh water and sewage move together. However, most of the bacterial spores seemed to originate from the land.The archipelago east of Tvärminne Storfjärd proved to be appropriate for inshore brackish‐water investigations being undisturbed by freshwater outflows.
Nutrient effect on maximum photosynthesis in arctic plants
Authors: Bigger C. Mollie , Oechel Walter C. 
Published: July 2006

The effect of a 1976 nitrogen, phosphorus, and nitrogen‐phosphorus‐potassium fertilization at Eagle Creek, Alaska, on photosynthetic rates was investigated in 1978 in eight vascular and three nonvascular plant species. While NPK fertilization increased the growth rate of shoots of most vascular plant species, this treatment depressed photosynthetic rates in all vascular species. Therefore, it appears that nutrient limitation of growth is a direct limitation and not mediated through nutrient effect on carbon uptake rates and levels of available photosynthate. The reason for the reduction in photosynthetic rates with fertilization is not known. It is speculated that increases in growth with fertilization causes a dilution of other nutrients or factors, the effect of which is to depress photosynthesis.Moss photosynthesis is stimulated with fertilization, High NPK fertilizer levels stimulate photosynthesis more than low NPK fertilizer levels. This may indicate basic differences in the ecology or physiology of the two growth forms. It is not yet known if the growth of mosses in this area is stimulated by NPK fertilization.
Profundal chironomid populations during a fertilization experiment in Langvatn, Norway
Authors: Aagaard Kaare 
Published: July 2006

Populations of Heterotrissocladius subpilosus and Phaenopsectra (Sergentia) coracina were studied from 1974 to 1978 in Langvatn, South‐Trøndelag, Norway. During 1975 and 1976 the lake was fertilized respectively by 1600 kg and 1000 kg fertilizer, (20% N, 4,8% P).Fertilization had a positive effect on primary production and zooplankton. The effect on the two chironomid species, which both need more than one year for development, was ambiguous. However, there was a positive relationship between the density of H. subpilosus larvae and the primary production.The number of P. (S.) coracina larvae steadily increased during the investigated period. Production estimates gave values in the range 0.6–1.5 g w.w. m−2 yr−1 for H. subpilosus and ca 2.3 g w.w. m−2 yr−1 for P. (S.) coracina.
The geology of Kaldvelladalen
Authors: Andersen A. B. , Rueslåtten H. G. 
Published: July 2006

Langvatn lake is a large waterfilled kettle hole in glaciofluvial deposits developed during the last deglaciation. The main outflow from the lake occurs by percolation through the permeable sediments at the shoreline.The sedimentary rocks and sediments (calcite bearing) within the watershed influence the quality of the lake waters.
Residue levels of organochlorine and mercury compounds in unhatched eggs and the relationships to breeding success in white‐tailed sea eagles Haliaeetus albicilla in Sweden
Authors: Helander Björn , Olsson Mats , Reutergårdh Lars 
Published: July 2006

Eighty‐five unhatched eggs from 68 white‐tailed sea eagle clutches were collected during 1965–1978 along the Baltic coast and in Lapland. The eggs were analysed individually for residue levels of DDT and its metabolites, PCB and mercury. Pooled samples were analysed for levels of dieldrin and hexachlorobenzene (HCB). The variations in residue levels within and between clutches were studied before the material was grouped for investigations of relationships between reproduction and contamination.Levels of DDE, PCB and mercury were significantly higher in the Baltic as compared to the Lapland material. In the Baltic, the reproductive success on a clutch basis and on a nest basis was significantly and negatively correlated to the egg residue levels of DDE and PCB; no correlation was found with mercury. Critical ranges were estimated to 500–600 mg kg1of DDE and/or 800–900 mg kg−1of PCB (lipid basis). The levels of dieldrin and HCB in the pooled samples were not considered important to reproduction. In a comparative study including six sea eagle and six bald eagle populations, productivity showed the strongest correlation with DDE.
Loss‐on‐ignition and carbon content in a beech forest soil profile
Authors: Christensen Bent Tolstrup , Malmros Per Åkesson 
Published: July 2006

The use of loss‐on‐ignition (LOI) and carbon content (C‐content) in estimating soil organic matter is examined. To evaluate the assumptions behind the use of these methods, the conversion factor (LOI/C‐content) is examined as a function of depth and spatial variability.Due to increasing variability with depth no general relationship between LOI and C‐content can be established for horizons below 60 cm. For horizons above 60 cm it is demonstrated, that more than one conversion factor is needed.The application of a regression equation to correct for inorganic losses is shown to be problematical. This is due to the variability in inorganic losses and the varying C‐content of the organic matter.
The climate of a Danish beech wood, Hestehaven, eastern Jutland
Authors: Rasmussen Søren , Nielsen Mogens Klitgaard , Hansen Jens P. N. 
Published: July 2006

The wind profile in the IBP beech stand and the vertical temperature distribution in the same beech stand and in a neighbouring clearing were investigated. In addition the temperature and humidity conditions in the trunk space of the beech stand and in the clearing were compared. The precipitation components were investigated during two periods.Because of the topography and the small extent of the wood the wind profile depends strongly on the wind direction. Maximum temperatures were found to occur in the upper part of the canopy during in‐leaf periods. During leafless periods the temperature distribution indicates the presence of two distinct levels of energy exchange, Advection of airmasses from the adjoining bay strongly influences the climate of the wood. Because of the density of trees and the narrow fanshaped canopies, yearly throughfalls amount to 55–60% of the total precipitation, while stemflows amount to as much as 12%.
Life histories, microdistribution and drift of two mayfly (Ephemeroptera) species in the Pembina River, Alberta, Canada
Authors: Ciborowski Jan J. H. , Clifford Hugh F. 
Published: July 2006

Ephemerella inermis Eaton is a univoltine species that emerges in July. Eggs hatch in August and larvae grow rapidly in autumn and spring, but not during winter. Baetis tricaudatus Dodds produces three cohorts per year. Emergence periods occur in early June, July and early September. Only one cohort overwinters as larvae.Microdistribution of both species is controlled largely by the discharge pattern of the river. During 1978, a year of frequent floods, animals were equally distributed among slow and fast water portions of the river. Nocturnal drift densities of both species were much greater in slow than in fast water areas. During 1979, a year of relatively stable flow, benthic larval densities were significantly greater in fast water than in slow water.Early instar E. inermis larvae are most abundant in nearshore areas, but move to deeper water in late autumn. Baetis tricaudatus larvae are seldom numerous in near‐shore areas.Densities of both species were positively associated with concentrations of detritus and of other invertebrates, but only when relationships were considered in areas of similar current velocity independently of season.
A two‐year study of leaf litter decomposition as related to macroclimatic factors and microarthropod abundance in the southern Appalachians
Authors: Seastedt T. R. , Crossley D. A. , Meentemeyer V. , Waide J. B. 
Published: July 2006

Chestnut oak Quercus prinus L. litter in the southern Appalachian Mountains of the United States decomposes slowly during winter and more rapidly in other seasons. This pattern differed from other studies of litter decomposition in more northern environments where decomposition rates were relatively constant throughout the year or more rapid beneath a winter snow cover. The pattern observed can be approximated by using monthly actual evapotranspiration estimates as a correction factor for the decomposition constant, k, in the commonly‐used negative exponential decomposition model.Mean microarthropod densities increased from a seasonally weighted estimate of 18.2 ind. g−1 litter during the first year of decomposition to 73.6 ind. g−1 litter during the second year. In spite of this increase, no difference in the rate of weight loss of the litter was observed between the first and second year of the study.
Changes in Danish farmland habitats and their populations of breeding birds
Authors: Møller Anders Pape 
Published: July 2006

Habitat changes and the breeding bird populations were studied at Kraghede, N Jutland the years 1970–1980. Generally, agricultural practice was intensified leading to an increase in the area used permanently for growing barley, and the abandonment of grasslands and meadows. Animal husbandry decreased, until it was restricted to a small number of farms.These habitat changes were the largest ones to occur in the Danish landscape for some 150–200 yr and had a significant influence on the breeding birds. Species confined to the meadows, such as the lapwing Vanellus vanellus, meadow pipit Anthus pratensis and others, decreased by 50–80% or even more. Species associated with the grassland when feeding, like the swallow Hirundo rustica, starling Sturnns vulgaris and magpie Pica pica, all had lower population levels at the end of the 1970's compared to those at the beginning of the decade.