Summary
Phytotron experiment 2005
During the last experimental phase (2004-2007) we integrate the competition related investigations on juvenile and adult trees under phytotron and field (Kranzberg Forest) conditions, respectively. The main focus is on the C allocation within the plants and to associated soil organisms. The overall goal is to capture the dynamics and to quantify the C allocation as well as the ontogenetic comparison between the evergreen Norway spruce ( Picea abies ) and deciduous European beech ( Fagus sylvatica ). The hypothesis is tested weather reduction of primary metabolism (experimentally generated by O 3 exposition) is limiting the C allocation to below ground (roots, mycorrhizae, soil organisms). In addition, we quantify the consequences of a limited C allocation below ground for the competitiveness for soil resources such as nitrogen.
During summer 2005, we analyze the established competition system (20 plants together in one soil container) under controlled conditions in the GSF phytotrons. Mono- and mixed cultures of juvenile beech and spruce are subjected to CO 2with changed 13d C t o study the C allocation as a function of intra-and interspecific competition under ambient and elevated O 3 concentrations. Stem and soil respiration is pursued after the change of the d13 C signal in the atmosphere to monitor changes in C allocation. Carbon isotope analyses of root and mycorrhizal fungal biomass (cooperation with B9 Pritsch/Hartmann) as well as to soil microbes (cooperation with B12 Munch/Schloter) is used to quantify belowground C-allocation. 15 N-labelling with ammonium nitrate allows the quantification of belowground competitiveness for N. In addition, the phytotron study under controlled conditions has a preparing character for the following field study in Kranzberg Forest.
During the following summer we work with adult beech and spruce trees in the field (Kranzberger Forst). Similar to the free-air O 3 exposure system, project B2 (Werner/Menzel) established a tube system for the application of 12C-labeled CO 2 in the canopy of the adult trees. Besides sampling of phloem sap, the C allocation will be monitored via the respiration signal from stems, coarse roots and soil. A 2-3 week d 13 CO 2 -labeling in August 2006 will allow the quantification of C allocation to roots and mycorrhizae (cooperation with B7 Raidl/Agerer).
In the field, 15 N allocation will be studied in cooperation with B4 (Häberle/Matyssek). Together with a similar 13 C- and 15 N-labeling in the lysimeter experiment (cooperation with B12 Munch/Schloter), the planned investigations will enable the ontogenetic scaling of C- und N allocation under various O 3 concentrations and competition set-ups
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