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| Hypothesis |
The hypothesis is being examined that beech with high turnover of resources responds more sensitively to disturbance than does spruce with lower turnover.
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| Experimental Design: |
To quantify competition, allocation of carbon, water and nutrients are analysed at the branch and whole plant level of 50 to 60 year old spruce and beech trees growing in a mixed forest (research station "Kranzberg Forest", Freising/ Germany). One branch of the sun and one in the shade crown in each of 10 spruce and 10 beech trees were selected, covering the entire range of branch and foliage differentiation in each individual. By means of detailed phenological assessments, structural and functional relationships are scaled from the branches across the crown to the whole-tree level. For unravelling the regulation of resource allocation (Fig.5) , ozone released from a 'free air' canopy exposure system is used as an experimental tool: 5 spruce and 5 beech trees are exposed to 2 x ambient O3 levels (150 ppb maximum; see B2 ) and compared in terms of their regulatory responsiveness with 'control' trees in unchanged air. Occupied canopy volume per unit of resource investment (Fig.1) , carbon returns from these investments per unit of occupied canopy volume (Fig.2), and the costs by transpiration (Fig.3) and respiration (Fig.4) in relation to the occupied volume express the competitive efficiencies of the trees. Such ratios enable for comparisons of competitiveness between and within trees (sun/shade), across ontogenetic stages (see companion Poster B5) and species (coniferous/deciduous). The assessment of belowground efficiency ratios will be intensified during SFB-phase II to complete this whole tree approach (see B4 concept poster).
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| Conclusions: |
In the sun crown spruce was 3 x as efficient in space occupation as beech (Fig.1) and at the same time only had a slightly higher carbon gain per unit of occupied volume (Fig.2) . It is to be expected that structural differences in space occupation determine competitiveness among neighbouring plants rather than primary production (SFB Hypothesis II).
Loss of leafmass and area through herbivory is not correlated to the C/N ratio of according leaves (not shown) (SFB Hypothesis V).
The shade branch of the beech operates near the zero-balance (Fig.2) , but has a very efficient space occupation (Fig.1) and low costs for respiration (Fig.3) and transpiration (Fig.4) in relation to the occupied volume, showing higher adaptation to low light levels compared to spruce.
Ozone is a reliable tool to interfere with the regulation of carbon allocation in mature trees (chlorotic mottling (not shown), senescence (Fig.5) ).
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