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  • 1
    Electronic Resource
    Electronic Resource
    Seasonal net carbon dioxide exchange of a beech forest with the atmosphere (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Global change biology 2 (1996), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: The seasonal carbon dioxide exchange of a beech forest of Central Italy was studied by means of the eddy covariance technique. Additional measurements of biomass respiration with cuvettes and relationship of carbon dioxide exchanges with temperature and light were used to interpolate missing data during the dormant and part of the growing season.The net ecosystem production of the forest equals 472 g C m−2 y−1 while the gross ecosystem production 1016 g C m−2 y−1 and respiration 544 g C m−2 y−1. These estimates are compared with the net primary production determined by direct biomass sampling which amounts to 802 g C m−2 y−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2486.1996.tb00072.x
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  • 2
    Electronic Resource
    Electronic Resource
    Long-term exposure to elevated [CO2] in a natural Quercus ilex L. community: net photosynthesis and photochemical efficiency of PSII at different levels of water stress (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 19 (1996), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Naturally grown trees of Mediterranean evergreen oak (Quercus ilex L.), representing the climax species of the region, were enclosed in six large open-top chambers and exposed to ambient and elevated CO2 concentrations during a 3 year period. Maximum daily net photosynthetic rates measured at the two different CO2 concentrations were from 30 to 100% higher in elevated than in ambient [CO2] throughout the experimental period. The increase in maximum daily photosynthesis was also accompanied by a 93% rise in the apparent quantum yield of CO2 assimilation, measured during periods of optimum soil moisture conditions. Hence, no clear evidence of down-regulation of net photosynthetic activity was found. Interactions between atmospheric CO2 concentration and plant water stress were studied by following the natural evolution of drought in different seasons and years. At each level of water stress, the maximum rate of carbon assimilation was higher in elevated than in ambient [CO2] by up to 100%.Analysis of in vivo chlorophyll fluorescence parameters in normal (21%) and low (2%) oxygen concentrations provided useful insights into the functioning and stability of the photosynthetic processes. The photochemical efficiency of PSII (Fv/Fm) progressively decreased as drought conditions became more evident; this trend was accentuated under elevated [CO2]. Thermal de-excitation processes were possibly more significant under elevated than under ambient [CO2], in a combination of environmental stresses.This research suggests two possible conclusions: (i) a ‘positive’ interaction between elevated [CO2] and carbon metabolism can be obtained through relief of water stress limitation in the summer months, and (ii) elevated [CO2], under drought conditions, may also enhance the significance of slow-relaxing quenching.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1996.tb00399.x
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  • 3
    Electronic Resource
    Electronic Resource
    Applications of a thermal imaging technique in the study of the ascent of sap in woody species (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 16 (1993), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: We present applications of infrared thermograph to the direct observation of water transport in stems of woody species. Presently, the method gives only qualitative information on the path of sap movement along the stem, and therefore, does not replace any of the common quantitative methods of sap flow measurement. Nevertheless, the thermal imaging technique provides a novel approach to the study of the ascent of sap and could have a role in supporting more quantitative methods. Thermography permits visualization of the thermal variations of a fairly large area of the stem in real time, and hence, is well suited for spatial analysis of sap movement. Three experiments were carried out during the summers of 1991 and 1992, with the following objectives: to define the sap flow distribution in the active annual rings; to identify grain anomalies in the sap wood; and to study the consequences of induced embolism on the path of sap flow. Altogether, we tested more than 10 woody species (broad-leaves and conifers) either in natural conditions or in the nursery. We found considerable differences in the spatial distribution of sap flow not only between species and individuals but also within a single tree. Grain anomalies or embolized zones in the xylem, which are easily demonstrated, often further modify the path of sap flow. The irregularity of sapwood dimensions and of sap flow among tree rings requires careful evaluation of the positioning of the probes when using methods for quantitative measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1993.tb00524.x
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  • 4
    Electronic Resource
    Electronic Resource
    An experimental test of the eddy correlation technique over a Mediterranean macchia canopy (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 14 (1991), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. Flux densities of water vapour and carbon dioxide were measured for a Mediterranean macchia canopy. Results show good agreement between the measured available energy and the sum of latent sensible and heat flux densities determined with the eddy correlation technique. Joint evaluation of the Bowen ratio, aerodynamic resistance, canopy resistance and the ‘omega factor’ suggests that the macchia canopy is intermediate in aerodynamic roughness between coniferous and deciduous canopies. Maximum daytime carbon flux densities ranged from -14 to -22(μnol m−2 s−1 on a ground area basis. The ratio of transpiration to assimilation (E/A) was a function of incident photo-synthetic photon flux density below about 400 μmol m−2s−1 and above it was fairly constant at 272 mol mol−1 (H2O/CO2). The relationship between carbon influx and canopy conductance was linear. Results show promising applications of the eddy correlation technique for evaluating physiological features of canopies, treated as unitary functional systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1991.tb00969.x
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  • 5
    Electronic Resource
    Electronic Resource
    In situ estimation of net CO2 assimilation, photosynthetic electron flow and photorespiration in Turkey oak (Q. cerris L.) leaves: diurnal cycles under different levels of water supply (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 18 (1995), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Diurnal time courses of net CO2 assimilation rates, stomatal conductance and light-driven electron fluxes were measured in situ on attached leaves of 30-year-old Turkey oak trees (Quercus cerris L.) under natural summer conditions in central Italy. Combined measurements of gas exchange and chlorophyll a fluorescence under low O2 concentrations allowed the demonstration of a linear relationship between the photochemical efficiency of PSII (fluorescence measurements) and the apparent quantum yield of gross photosynthesis (gas exchange). This relationship was used under normal O2 to compute total light-driven electron fluxes, and to partition them into fractions used for RuBP carboxylation or RuBP oxygenation. This procedure also yielded an indirect estimate of the rate of photorespiration in vivo. The time courses of light-driven electron flow, net CO2 assimilation and photorespiration paralleled that of photosynthetic photon flux density, with important afternoon deviations as soon as a severe drought stress occurred, whereas photochemical efficiency and maximal fluorescence underwent large but reversible diurnal decreases. The latter observation indicated the occurrence of a large non-photochemical energy dissipation at PSII. We estimated that less than 60% of the total photosynthetic electron flow was used for carbon assimilation at midday, while about 40% was devoted to photorespiration. The rate of carbon loss by photorespiration (R1) reached mean levels of 56% of net assimilation rates. The potential application of this technique to analysis of the relative contributions of thermal de-excitation at PSII and photorespiratory carbon recycling in the protection of photosynthesis against stress effects is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1995.tb00564.x
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  • 6
    Electronic Resource
    Electronic Resource
    Bridging a Transected Rat Optic Nerve with a Semipermeable Guidance Channel (1987)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 495 (1987), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1987.tb23743.x
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