The growth of beech and spruce – representative for trees in general -, as well as their interspecific competition, are influenced by a range of natural factors such as weather, water and nutriments. These dependences are investigated within the interdisciplinary SFB 607, for ambient and elevated ozone regimes. Ozone largely represents an abiotic stress factor, but also provides a key for the quantification of chronic ozone effects. For this purpose, a novel Free-Air-Ozone-Fumigation system was deployed in 10 canopies of approximately 60 years old beech and spruce trees, at the KBF experimental site. The fumigation mode was adjusted for continuously doubling actual ozone levels within the fumigation zone, with maximum values being limited to 150 ppb.
One purpose of the present work was to document, with high spatial resolution, the ozone distribution within the entire intensive measuring area (about 50 x 50 m) and to control the fate of the artificial “ozone cloud”. This monitoring thus implied numerous measuring points (over 100 )which was realized through an economic system of passive samplers. High priced UV ozone monitors (8 during the last development phase) provided continuous measurements of the controlled variable in the Free-Air-Ozone-Fumigation, as well as for calibration of the passive samplers. They were also used for the investigation of concentration processes of high temporal resolution. For the passive sampler measurement, a new diffusion sampler, based on a deposition sampler, was designed (labeled type D). With its help, the integrative ozone concentration could be defined during the time of exposure.
This diffusion sampler constitutes a “multi tube sampler” which provides wind-independent measurements. This is achieved by a diffuser consisting of approximately 320 glass capillaries fixed in front of the sensor surface. Its high functionality which is almost independent of incedent flow velocities and ambient meteorological parameters could be proved in tests in wind tunnels and climate chambers.
Comparative measurements with UV ozone monitors operating in parallel, persistently showed a high correlation of r² ≥ 0.82. The passive samplers were fixed at cords and pulled into the right position like a flag on a flagstaff. The mounting brackets consisted of high-grade steel clamps developed for this purpose. On the one hand, they allowed a simple and fast exchange, and on the other hand, they ensured a horizontal alignment of the passive sampler system. To protect the samplers from solar radiation and rain, they were exposed in a specially designed and well aerated security box. Over several vegetation periods, the measurements by means of the passive samplers provided data on the dispersion and homogeneity of the ozone cloud, documented as horizontal and vertical isoplots of weekly averages. The enhancement factor of “2” was persistently achieved throughout the artificial ozone fumigation zone, whereas the surrounding reference trees remained untouched by the administered ozone.
By means of the diffusion passive sampler measurements, it was possible to determine the actual SUM0 values, which enable to estimate the ozone flux into the plants. As passive sampler measurements do not cover the underlying temporal dynamic of the ozone concentration, the determination of AOT40 values was difficult. However, this problem could be solved with an AOT40 forecasting model. In comparison with the values evaluated with UV ozone monitor measurements, the predicted AOT40 values showed a correlation of r² = 0.71 for the year 2005 and of r² = 0.82 for the year 2006. These results are considered as “good”.
The ozone distribution could be documented by means of the 8 UV ozone monitors and 100 ozone passive samplers used during the last stage of development at the KBF. However, to exactly determine the plant-effective assimilation of ozone into the leaves, the stomatic resistance, the boundary layer resistance, and its reciprocal values, i.e. its respective conductivity have to be known. Different from the stomatic conductivity, which can precisely be determined by using a diffusion porometer, the conductivity of the boundary layer depends on the incident flow and other factors that are difficult to measure. Therefore, model calculations for the estimation of stomatic ozone flux do not consider the variability of the boundary layer conductivity or its resistance. On the basis of these considerations, another purpose of this work was to develop a “micro passive sampler”, which, due to its geometry, enables to directly measure the ozone deposition on the leaf surface. Thus, the disposition of the temporarily variable boundary layer resistance necessary for modeling the ozone transport rate, could be omitted. The development of the “micro passive samplers” however, proved to be extremely difficult and considerably more time consuming and cost intensive than originally planned. Based on a multitude of development attempts, the most promising development direction points to the use of a standard printer in combination with a standard printer foil as carrier layer. A reproducible, homogeneous and ozone-sensitive layer could be applied to the foil via inkjet print technology. The ink thereby used consisted of a specially developed Indigo ink. The imprinted layer of Indigo showed a spectrometically detectable reduction of the Indigo peak, which proved to be dependent of the ozone application rate. Because of the low ozone concentrations expected directly at the leaf surfaces, the achieved signal change, however, is too marginal for conducting ozone deposition measurements with sufficient accuracy. Nevertheless, the feasibility could be shown by the development of the ozone sensitive foil, which is a kind of prototype of a micro passive sampler.
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The growth of beech and spruce – representative for trees in general -, as well as their interspecific competition, are influenced by a range of natural factors such as weather, water and nutriments. These dependences are investigated within the interdisciplinary SFB 607, for ambient and elevated ozone regimes. Ozone largely represents an abiotic stress factor, but also provides a key for the quantification of chronic ozone effects. For this purpose, a novel Free-Air-Ozone-Fumigation system was...
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