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Carbon dioxide exchange and isotopic signature (13C) of an unmanaged 250-year-old deciduous forest (2004)

Knohl, Alexander

Göttingen : Forschungszentrum Waldökosysteme

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Call number: ZS-015(A 188)

In: Berichte des Forschungszentrums Waldökosysteme

Type of Medium: Series available for loan

Pages: IV, 97 S., S. V - VI , graph. Darst.

Series Statement: Berichte des Forschungszentrums Waldökosysteme : Reihe A 188

Classification:

Ecology

Note: Zugl.: Jena, Univ., Diss., 2003

Location: Lower compact magazine

Branch Library: GFZ Library

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Europe-wide reduction in primary productivity caused by the heat and drought in 2003 (2005)

Reichstein, M. ; Viovy, N. ; Granier, A. ; [et al.]

[s.l.] : Nature Publishing Group

Nature 437 (2005), S. 529-533

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ISSN: 1476-4687

Source: Nature Archives 1869 - 2009

Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics

Notes: [Auszug] Future climate warming is expected to enhance plant growth in temperate ecosystems and to increase carbon sequestration. But although severe regional heatwaves may become more frequent in a changing climate, their impact on terrestrial carbon cycling is unclear. Here we report measurements of ...

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1038/nature03972

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Carbon dioxide exchange of a Russian boreal forest after disturbance by wind throw (2002)

Knohl, Alexander ; Kolle, Olaf ; Minayeva, Tatiana Y. ; [et al.]

Oxford, UK : Blackwell Science Ltd

Global change biology 8 (2002), S. 0

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ISSN: 1365-2486

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography

Notes: The exchange of carbon dioxide (CO2) between the atmosphere and a forest after disturbance by wind throw in the western Russian taiga was investigated between July and October 1998 using the eddy covariance technique. The research area was a regenerating forest (400 m × 1000 m), in which all trees of the preceding generation were uplifted during a storm in 1996. All deadwood had remained on site after the storm and had not been extracted for commercial purposes. Because of the heterogeneity of the terrain, several micrometeorological quality tests were applied. In addition to the eddy covariance measurements, carbon pools of decaying wood in a chronosequence of three different wind throw areas were analysed and the decay rate of coarse woody debris was derived.During daytime, the average CO2 uptake flux was −3 µmol m−2s−1, whereas during night-time characterised by a well-mixed atmosphere the rates of release were typically about 6 µmol m−2s−1. Suppression of turbulent fluxes was only observed under conditions with very low friction velocity (u* ≤ 0.08 ms−1). On average, 164 mmol CO2 m−2d−1 was released from the wind throw to the atmosphere, giving a total of 14.9 mol CO2 m−2 (180 g CO2 m−2) released during the 3-month study period.The chronosequence of dead woody debris on three different wind throw areas suggested exponential decay with a decay coefficient of −0.04 yr−1. From the magnitude of the carbon pools and the decay rate, it is estimated that the decomposition of coarse woody debris accounted for about a third of the total ecosystem respiration at the measurement site. Hence, coarse woody debris had a long-term influence on the net ecosystem exchange of this wind throw area.From the analysis performed in this work, a conclusion is drawn that it is necessary to include into flux networks the ecosystems that are subject to natural disturbances and that have been widely omitted into considerations of the global carbon budget. The half-life time of about 17 years for deadwood in the wind throw suggests a fairly long storage of carbon in the ecosystem, and indicates a very different long-term carbon budget for naturally disturbed vs. commercially managed forests.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1046/j.1365-2486.2002.00475.x

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On the separation of net ecosystem exchange into assimilation and ecosystem respiration: review and improved algorithm (2005)

Reichstein, Markus ; Falge, Eva ; Baldocchi, Dennis ; [et al.]

Oxford, UK : Blackwell Science Ltd

Global change biology 11 (2005), S. 0

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ISSN: 1365-2486

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography

Notes: This paper discusses the advantages and disadvantages of the different methods that separate net ecosystem exchange (NEE) into its major components, gross ecosystem carbon uptake (GEP) and ecosystem respiration (Reco). In particular, we analyse the effect of the extrapolation of night-time values of ecosystem respiration into the daytime; this is usually done with a temperature response function that is derived from long-term data sets. For this analysis, we used 16 one-year-long data sets of carbon dioxide exchange measurements from European and US-American eddy covariance networks. These sites span from the boreal to Mediterranean climates, and include deciduous and evergreen forest, scrubland and crop ecosystems.We show that the temperature sensitivity of Reco, derived from long-term (annual) data sets, does not reflect the short-term temperature sensitivity that is effective when extrapolating from night- to daytime. Specifically, in summer active ecosystems the long-term temperature sensitivity exceeds the short-term sensitivity. Thus, in those ecosystems, the application of a long-term temperature sensitivity to the extrapolation of respiration from night to day leads to a systematic overestimation of ecosystem respiration from half-hourly to annual time-scales, which can reach 〉25% for an annual budget and which consequently affects estimates of GEP. Conversely, in summer passive (Mediterranean) ecosystems, the long-term temperature sensitivity is lower than the short-term temperature sensitivity resulting in underestimation of annual sums of respiration.We introduce a new generic algorithm that derives a short-term temperature sensitivity of Reco from eddy covariance data that applies this to the extrapolation from night- to daytime, and that further performs a filling of data gaps that exploits both, the covariance between fluxes and meteorological drivers and the temporal structure of the fluxes. While this algorithm should give less biased estimates of GEP and Reco, we discuss the remaining biases and recommend that eddy covariance measurements are still backed by ancillary flux measurements that can reduce the uncertainties inherent in the eddy covariance data.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1365-2486.2005.001002.x

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Forest and agricultural land-use-dependent CO2 exchange in Thuringia, Germany (2004)

Anthoni, P. M. ; Knohl, A. ; Rebmann, C. ; [et al.]

Oxford, UK : Blackwell Science Ltd

Global change biology 10 (2004), S. 0

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ISSN: 1365-2486

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography

Notes: Eddy covariance was used to measure the net CO2 exchange (NEE) over ecosystems differing in land use (forest and agriculture) in Thuringia, Germany. Measurements were carried out at a managed, even-aged European beech stand (Fagus sylvatica, 70–150 years old), an unmanaged, uneven-aged mixed beech stand in a late stage of development (F. sylvatica, Fraxinus excelsior, Acer pseudoplantanus, and other hardwood trees, 0–250 years old), a managed young Norway spruce stand (Picea abies, 50 years old), and an agricultural field growing winter wheat in 2001, and potato in 2002. Large contrasts were found in NEE rates between the land uses of the ecosystems. The managed and unmanaged beech sites had very similar net CO2 uptake rates (∼−480 to −500 g C m−2 yr−1). Main differences in seasonal NEE patterns between the beech sites were because of a later leaf emergence and higher maximum leaf area index at the unmanaged beech site, probably as a result of the species mix at the site. In contrast, the spruce stand had a higher CO2 uptake in spring but substantially lower net CO2 uptake in summer than the beech stands. This resulted in a near neutral annual NEE (−4 g C m−2 yr−1), mainly attributable to an ecosystem respiration rate almost twice as high as that of the beech stands, despite slightly lower temperatures, because of the higher elevation. Crops in the agricultural field had high CO2 uptake rates, but growing season length was short compared with the forest ecosystems. Therefore, the agricultural land had low-to-moderate annual net CO2 uptake (−34 to −193 g C m−2), but with annual harvest taken into account it will be a source of CO2 (+97 to +386 g C m−2). The annually changing patchwork of crops will have strong consequences on the regions' seasonal and annual carbon exchange. Thus, not only land use, but also land-use history and site-specific management decisions affect the large-scale carbon balance.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1365-2486.2004.00863.x

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Productivity of forests in the Eurosiberian boreal region and their potential to act as a carbon sink –- a synthesis (1999)

Schulze, E. -D. ; Lloyd, J. ; Kelliher, F. M. ; [et al.]

Oxford, UK : Blackwell Science Ltd

Global change biology 5 (1999), S. 0

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ISSN: 1365-2486

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography

Notes: Based on review and original data, this synthesis investigates carbon pools and fluxes of Siberian and European forests (600 and 300 million ha, respectively). We examine the productivity of ecosystems, expressed as positive rate when the amount of carbon in the ecosystem increases, while (following micrometeorological convention) downward fluxes from the atmosphere to the vegetation (NEE = Net Ecosystem Exchange) are expressed as negative numbers. Productivity parameters are Net Primary Productivity (NPP=whole plant growth), Net Ecosystem Productivity (NEP = CO2 assimilation minus ecosystem respiration), and Net Biome Productivity (NBP = NEP minus carbon losses through disturbances bypassing respiration, e.g. by fire and logging). Based on chronosequence studies and national forestry statistics we estimate a low average NPP for boreal forests in Siberia: 123 gC m–2 y–1. This contrasts with a similar calculation for Europe which suggests a much higher average NPP of 460 gC m–2 y–1 for the forests there. Despite a smaller area, European forests have a higher total NPP than Siberia (1.2–1.6 vs. 0.6–0.9 × 1015 gC region–1 y–1). This arises as a consequence of differences in growing season length, climate and nutrition. For a chronosequence of Pinus sylvestris stands studied in central Siberia during summer, NEE was most negative in a 67-y old stand regenerating after fire (– 192 mmol m–2 d–1) which is close to NEE in a cultivated forest of Germany (– 210 mmol m–2 d–1). Considerable net ecosystem CO2-uptake was also measured in Siberia in 200- and 215-y old stands (NEE:174 and – 63 mmol m–2 d–1) while NEP of 7- and 13-y old logging areas were close to the ecosystem compensation point. Two Siberian bogs and a bog in European Russia were also significant carbon sinks (– 102 to – 104 mmol m–2 d–1). Integrated over a growing season (June to September) we measured a total growing season NEE of – 14 mol m–2 summer–1 (– 168 gC m–2 summer–1) in a 200-y Siberian pine stand and – 5 mol m–2 summer–1 (– 60 gC m–2 summer–1) in Siberian and European Russian bogs. By contrast, over the same period, a spruce forest in European Russia was a carbon source to the atmosphere of (NEE: + 7 mol m–2 summer–1 = + 84 gC m–2 summer–1). Two years after a windthrow in European Russia, with all trees being uplifted and few successional species, lost 16 mol C m–2 to the atmosphere over a 3-month in summer, compared to the cumulative NEE over a growing season in a German forest of – 15.5 mol m–2 summer–1 (– 186 gC m–2 summer–1; European flux network annual averaged – 205 gC m–2 y–1). Differences in CO2-exchange rates coincided with differences in the Bowen ratio, with logging areas partitioning most incoming radiation into sensible heat whereas bogs partitioned most into evaporation (latent heat). Effects of these different surface energy exchanges on local climate (convective storms and fires) and comparisons with the Canadian BOREAS experiment are discussed. Following a classification of disturbances and their effects on ecosystem carbon balances, fire and logging are discussed as the main processes causing carbon losses that bypass heterotrophic respiration in Siberia. Following two approaches, NBP was estimated to be only about 13–16 mmol m–2 y–1 for Siberia. It may reach 67 mmol m–2 y–1 in North America, and about 140–400 mmol m–2 y–1 in Scandinavia. We conclude that fire speeds up the carbon cycle, but that it results also in long-term carbon sequestration by charcoal formation. For at least 14 years after logging, regrowth forests remain net sources of CO2 to the atmosphere. This has important implications regarding the effects of Siberian forest management on atmospheric concentrations. For many years after logging has taken place, regrowth forests remain weaker sinks for atmospheric CO2 than are nearby old-growth forests.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1046/j.1365-2486.1999.00266.x

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Pan-European δ13C values of air and organic matter from forest ecosystems (2005)

Hemming, Deborah ; Yakir, Dan ; Ambus, Per ; [et al.]

Oxford, UK : Blackwell Science Ltd

Global change biology 11 (2005), S. 0

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ISSN: 1365-2486

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography

Notes: We present carbon stable isotope, δ13C, results from air and organic matter samples collected during 98 individual field campaigns across a network of Carboeuroflux forest sites in 2001 (14 sites) and 2002 (16 sites). Using these data, we tested the hypothesis that δ13C values derived from large-scale atmospheric measurements and models, which are routinely used to partition carbon fluxes between land and ocean, and potentially between respiration and photosynthesis on land, are consistent with directly measured ecosystem-scale δ13C values. In this framework, we also tested the potential of δ13C in canopy air and plant organic matter to record regional-scale ecophysiological patterns.Our network estimates for the mean δ13C of ecosystem respired CO2 and the related ‘discrimination’ of ecosystem respiration, δer and Δer, respectively, were −25.6±1.9‰ and 17.8 ±2.0‰ in 2001 and −26.6±1.5‰ and 19.0±1.6‰ in 2002. The results were in close agreement with δ13C values derived from regional-scale atmospheric measurement programs for 2001, but less so in 2002, which had an unusual precipitation pattern. This suggests that regional-scale atmospheric sampling programs generally capture ecosystem δ13C signals over Europe, but may be limited in capturing some of the interannual variations.In 2001, but less so in 2002, there were discernable longitudinal and seasonal trends in δer. From west to east, across the network, there was a general enrichment in 13C (∼3‰ and ∼1‰ for the 2 years, respectively) consistent with increasing Gorczynski continentality index for warmer and drier conditions. In 2001 only, seasonal 13C enrichment between July and September, followed by depletion in November (from about −26.0‰ to −24.5‰ to −30.0‰), was also observed. In 2001, July and August δer values across the network were significantly related to average daytime vapor pressure deficit (VPD), relative humidity (RH), and, to a lesser degree, air temperature (Ta), but not significantly with monthly average precipitation (Pm). In contrast, in 2002 (a much wetter peak season), δer was significantly related with Ta, but not significantly with VPD and RH. The important role of plant physiological processes on δer in 2001 was emphasized by a relatively rapid turnover (between 1 and 6 days) of assimilated carbon inferred from time-lag analyses of δer vs. meteorological parameters. However, this was not evident in 2002. These analyses also noted corresponding diurnal cycles of δer and meteorological parameters in 2001, indicating a rapid transmission of daytime meteorology, via physiological responses, to the δer signal during this season.Organic matter δ13C results showed progressive 13C enrichment from leaves, through stems and roots to soil organic matter, which may be explained by 13C fractionation during respiration. This enrichment was species dependent and was prominent in angiosperms but not in gymnosperms. δ13C values of organic matter of any of the plant components did not well represent short-term δer values during the seasonal cycle, and could not be used to partition ecosystem respiration into autotrophic and heterotrophic components.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1365-2486.2005.00971.x

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Hyperfeinstruktur des 82P3/2-Terms von Cäsium 134 (1968)

Knohl, U. ; Putlitz, G. zu ; Schenck, A.

Springer

The European physical journal 208 (1968), S. 364-366

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ISSN: 1434-601X

Source: Springer Online Journal Archives 1860-2000

Topics: Physics

Notes: Abstract The electric quadrupole interaction constantB of the 8p2P3/2 state of Cs134 has been determined by an optical double resonance measurement of the hyperfine structure transition vF=11/2−F=9/2=47.84(12) Mc/s. The results are: B 8P 134 =8.06(20) Mc/s and Q 8P 134 =+ 0.427(8) · 10−24cm2. Comparison is made between the measurements in the 7p and 8p electronic states: Q 8P 134 /Q 7P 134 =0.977(20). The ratio of the corresponding Sternheimer correction factors yields the value C7p/C8P=0.982.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01382698

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Elektrisches Kernquadrupolmoment von Cäsium 134 (1968)

Heinzelmann, G. ; Knohl, U. ; Putlitz, G. zu

Springer

The European physical journal 211 (1968), S. 20-34

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ISSN: 1434-601X

Source: Springer Online Journal Archives 1860-2000

Topics: Physics

Notes: Abstract The hyperfine structure splitting of the 72 P 3/2 state of Cs134 has been measured by optical double resonance spectroscopy in zero magnetic field. The following interaction constants have been obtained: Magnetic hfs constantA(72 P 3/2, Cs134)=16.851 (16) MHz. Quadrupole coupling constantB(72 P 3/2, Cs134)=18.07 (12) MHz. Then the electric quadrupole moment of Cs134 can be calculatedQ hfs(Cs134)=+0.436 (3) barn without Sternheimer correction, andQ(Cs134)=+0.356(2) barn with Sternheimer correction. A method for the production of alkali resonance cells with quantities of less than 1014 atoms of the radioactive isotope is described.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01421337

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