At Kranzberg Forest near Freising/Germany the competitive interaction between beech and spruce trees of a 40 to 60-year-old mixed forest stand is being analyzed through ecophysiological methodology. Major emphasis is on the carbon and water relations of the trees. Since the competitiveness of a plant is determined by the integral across structure and function, efficiency ratios have been defined for quantifying this synergy, i.e. in space sequestration (resource investment per unit of crown and soil volume), resource acquisition (resource gain per unit of resource investment and occupied volume), and resource costs (transpiration, respiration) for sustaining structure-related resource gains. In addition, regulatory responsiveness towards disturbance is crucial for maintaining competitiveness. As an experimental agent of disturbance, ozone has been selected which is being applied through a novel "free-air" ozone fumigation system, successfully brought into operation by FABIAN/B2 during phase I of the experiment. By means of this system, the common canopy of a group of 10 neighboring, adult trees (five per species) is being exposed to an elevated ozone regime by computer-aided, feedback control: Through doubling (up to a maximum of 150 ppb O3) of the prevalent, ambient ozone regime, a chronic disturbance of the carbon and water relations is generated in a site-relevant way. Another group of 10 trees in unchanged, ambient air serves as a "control". For analyzing the chronic impact, assessments of carbon balances at the branch and up-scaling to the whole-tree and stand level (cooperation with PRETZSCH, B1 & C3) is being continued throughout phase II of the experiment; research on belowground processes is being intensified.
The hypothesis is that beech responds more sensitive in its competitiveness to the enhanced ozone regime with respect to resource turnover than does the more conservative spruce. This hypothesis is being extended in phase II in that beech tends to compensate, via lammas shoot formation, for the ozone effect on the remainder of the foliage. This kind of compensation is expected to be accomplished at the expense of root development.
In consistency with the approach pursued on the branches, carbon turnover (biomass development, respiration) and water uptake is being followed by means of gas exchange and sap flow measurements (cooperation with B7, B9, B10 and KAZDA/Ulm). For reaching the stand level, a novel geo-radar approach for assessing, in a non-destructive way, the coarse-root system will be employed, along with core-sampling for estimating the fine-root biomass. In the canopy, measurements of leaf gas exchange, sap flow through stem and branches, branch and stem respiration and increment, space sequestration and (bio)chemical composition are being continued (cooperation with A1, RENNENBERG/Freiburg, GRILL/Graz, HANKE/Cambridge, UK) in order to distinguish alterations in the carbon and water relations relative to findings of the preceding years. Stable isotope analysis (12C/13C) of leaves and wood will aid assessments of changes in the water-use efficiency (cooperation with B6). In addition, the influence of phytophages and pathogens on the production and metabolic defense capacity is determined, as naturally occurring at the site. In comparison with the experiment on the young beech and spruce trees conducted in the GSF-phytotrons (see B5), "ontogenetic scaling" becomes accessible of processes which are crucial for the balance between competitiveness towards neighboring plants and parasite defense.
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Individuelle Unterschiede in herbstlicher Laubfärbung von Buchenkronen
Im Versuchsbestand sind 3 Gerüsttürme mit 4 Plattformen zwischen 17 und 25m Höhe miteinander verbunden.
Meßkopf des Porometers LICOR 6400 in einer Fichtenkrone
Annette Jungermann (Dipl.Ing.Forst (FH)) und Ilja Reiter (Dipl. Biol.) bei Gaswechselmessungen an Fichte
Die Plattformen zwischen den Gerüsttürmen sind vom Boden aus erst nach dem Laubfall zu sehen
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