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491.
Michael Dannenmann Rainer Gasche Astrid Ledebuhr Thomas Holst Helmut Mayer Hans Papen 《European Journal of Forest Research》2007,126(2):331-346
The effect of forest management (thinning) on in situ carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) trace gas exchange between soil and atmosphere was studied in three consecutive years at three beech forest sites, which
differ in aspect [southwest (SW), northeast (NE), northwest (NW)]. At all sites adjacent thinning plots (“T”) and untreated
control plots (“C”) were established. Measurements at the SW and NE sites covered the years 4–6 after thinning while at the
NW site measurements covered the year before and the first 2 years after thinning. Mean N2O fluxes were <3 μg N2O–N m−2 h−1 at all plots except for the newly thinned NWT plot. CH4 uptake was rather low, too. Very low CH4 oxidation rates during dry periods are explained by physiological drought stress for CH4 oxidizers. Heterotrophic litter decomposition constitutes the largest part of total soil respiration. On the whole, no significant
positive or negative effects of the silvicultural treatment on the magnitude of CO2-, CH4- and N2O-trace gas exchange could be observed at the SW site 4–6 years after thinning. Also at the NE site, no effects of thinning
on CO2 and N2O fluxes could be demonstrated. However, at this site a significant moisture-induced lower CH4 uptake could be shown. At the NW site forest management led to a dramatic increase in N2O emissions in the first two summers after thinning and to distinct effects on CO2 emissions and CH4 uptake in the first year after the felling. The unambiguous effects of thinning at the NW site are mainly related to higher
C input by dead residues leading to enhanced mineralization activity, to a shift in the competition for nutrients favoring
microorganisms as compared to trees and to changes in the soil water availability at the thinned plot. Considering the data
obtained from the NE and SW site we expect that with the development of an understorey vegetation at the NW site the observed
effects on the magnitude of trace gas exchange due to thinning will continue to decline in the following years. Our results
implicate that it is indispensable to take account of the effects of forest management in order to accurately calculate trace
gas emission inventories for the investigated forest ecosystem in case thinning took place immediately before. 相似文献
492.
Michael Nahm Thomas Holst Andreas Matzarakis Helmut Mayer Heinz Rennenberg Arthur Geßler 《European Journal of Forest Research》2006,125(1):1-14
We assessed seasonal changes of total soluble nonprotein nitrogen compounds (TSNN) in adult European beech trees (Fagus sylvatica, L.) growing under different local climate during the growing season immediately following a thinning treatment and 3 years
later. In both years, samples of leaves, xylem sap and phloem exudates from beech trees growing in thinned and unthinned (control)
stands on a dry, warm SW exposed and a cooler, moist NE exposed site were collected in May, July and September. In May of
both years, asparagine (Asn) and glutamine (Gln) were most abundant in leaves and xylem, respectively, whereas arginine (Arg)
dominated in the phloem. In July, TSNN concentrations decreased in all tissues and sites, but differences in water availability
between aspects were reflected in TSNN concentrations. In September, differences in the increase of Arg concentration in the
phloem were related to differences in the onset of senescence between treatments. Thinning treatment increased amino compound
concentrations of beech tissues in July on both aspects, particularly at the NE thinned site. It is supposed that, the N balance
of adult beech is favoured by both, the thinning treatments as well as the cool-moist climate prevailing at the NE aspect. 相似文献
493.
Filtering of Sulfur compounds from air by beech forest In a mature beech (Fagus silvatica) forest the amounts of sulfate-S per ha and year in open land precipitation, throughfall, stem flow and seepage in 100 cm soil depth have been measured from 1969 to 1976. From the fluxes measured quantitative data on plant leaching and dry deposition in the form of plant filtering are derived. Dry deposition amounts to 26kg S · ha?1 · y?1 and is of the same size as wet deposition (24 kg). The leaching of sulfate takes place only in autumn and amounts to ca. 3 kg S. The acid soil in the range of Al-buffering increases its sulfate storage annually by ca. 17 kg S/ha. 相似文献
494.
LC Venema JWG Wildoer JW Janssen SJ Tans HLJT Tuinstra LP Kouwenhoven C Dekker 《Science (New York, N.Y.)》1999,283(5398):52-55
Carbon nanotubes provide a unique system for studying one-dimensional quantization phenomena. Scanning tunneling microscopy was used to observe the electronic wave functions that correspond to quantized energy levels in short metallic carbon nanotubes. Discrete electron waves were apparent from periodic oscillations in the differential conductance as a function of the position along the tube axis, with a period that differed from that of the atomic lattice. Wave functions could be observed for several electron states at adjacent discrete energies. The measured wavelengths are in good agreement with the calculated Fermi wavelength for armchair nanotubes. 相似文献
495.
LC GOLLAND DR HODGSON RE DAVIS RJ RAWLINSON MB COLLINS SA McCLINTOCK DR HUTCHINS 《Australian veterinary journal》1995,72(5):161-164
SUMMARY A retrospective study of 46 horses with retropharyngeal lymph node (RPLN) infection presented to the Rural Veterinary Centre between 1977 and 1992 was undertaken. Horses aged less than one year were most commonly represented (46%). Thirty-nine percent of cases had been exposed to horses with confirmed or suspected strangles (Streptococcus equi subsp equi infection) within the previous 8 weeks. Most frequent signs were unilateral or bilateral swelling of the throat region (65%), respiratory stertor/dyspnoea (35%), purulent nasal discharge (20%), inappetence and signs of depression (15%), and dysphagia (9%). All horses had a soft tissue density in the retropharyngeal region on radiographs. Rhinopharyngoscopy, ultrasonography, haematology as well as cytological and microbial analysis of material aspirated from the soft tissue swelling facilitated diagnosis in some horses. Fifteen horses (33%) were treated with procaine penicillin intramuscularly for 4 to 7 days followed by oral trimethoprim-sulphadimidine for 7 to 14 days. Non-steroidal anti-inflammatory drugs were administered to 6 horses. Four required tracheostomy for severe respiratory distress. The 15 horses treated medically responded to treatment and were discharged from hospital. Three horses (6%) with mild signs received no treatment and recovered uneventfully. Twenty-eight horses (61%) underwent general anaesthesia and surgical drainage of a RPLN abscess. Nineteen received procaine penicillin G for 4 to 7 days. Four of the nine horses that did not receive antibiotic treatment after surgery required further surgical drainage 10 days to 7 weeks after the initial surgery . Limited follow-up information was available for 37 horses. Thirty-two horses were considered to have made complete recovery, 3 horses had died through misadventure and 2 had been euthanased because of chronic ill-thrift . 相似文献