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| Summary |
The study is focusing on the analysis of the competitiveness of young beech and spruce plants as growing in mixed plantations in a phytotron experiment (conducted at the GSF research center). Ten beech and spruce individuals each are grown together in containers (arrangement 4 x 5 plants, soil volume about 0.1 m3, total of 32 containers in 4 phytotrons), where emphasis is being directed to the analysis of the six individuals located in the central area of each container. Disturbants affecting competition are imposed on these systems as analytical tools and driving factors in resource allocation:
(1) chronic exposure throughout two years to ambient or twice-ambient ozone levels for disturbing aboveground interaction. The first year ensures acclimation to the ozone regimes through stimulation of the secondary metabolism. In parallel, the carbon flux into the soil via the sink strength of mycorrhizal roots and soil micro-organisms is being assessed.
(2) During the second growing season, Phytophthora citricola is being employed as an additional disturbant in the root zone (cooperation with OßWALD & FLEISCHMANN/A6). This root pathogen is introduced at the time of the lammas shoot formation in beech which is distinctly more sensitive to this parasite than spruce. With regard to competitiveness, beech is confronted with the conflict between lammas shoot growth (as one strategy of crown extension) and defense against the root parasite. The hypothesis is being examined that chronic ozone stress enhances the resistance of beech against Phytophthora infestation, although the elevated defense capacity is accomplished at the expense of the competitiveness towards spruce.
As a consistent continuation of the concept pursued during phase I of the project, competitiveness is being quantified as an aspect of resource allocation with respect to the efficiencies in space sequestration (resource investment per unit of occupied above and belowground space), resource acquisition (resource gain per investment and occupied space), and "running costs" (transpiration, respiration per resource gain and occupied space). For this purpose, carbon and water balances as well as respiratory costs and biomass production are being assessed for the above and belowground plant organs. The assessment of carbon and nitrogen partitioning within plants is aided through stable-isotope analysis (labelling with 13C via the gas phase, and with 15N through liquid fertilization; cooperation with LÖTSCHER/B13). Phenology and allometric development will be related to hormonal analyses (cytokinins, ABA) by HANKE (Cambridge, UK).
Particular attention is being directed during project phase II to the carbon flux from the foliage to the soil, including the related resource turnover ("13C pulse-chase approach", cooperation with LÖTSCHER/B6). Responses will be determined by species (beech, spruce) and treatments (ozone, Phytophthora), and the respiration of mycorrhizal roots will be compared with that of the soil micro-organisms (cooperation with ANDERSEN, Corvallis/USA, and HARTMANN/B9). Dynamics of root growth are being pursued by means of "in-growth" cylinders, root windows and a camera-based mini-rhizotrone approach (image-processing; cooperation with KAZDA, Ulm).
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