Integrated analysis of relationships between 3D-structure, leaf photosynthesis, and branch transpiration of mature Fagus sylvatica and Quercus petraea trees in a mixed forest stand
Identifying the relevance of forest structure for stand photosynthesis and transpiration is one of the remaining challenges in plant physiological ecology. This thesis uses the historically new chances for the description of 3D-complexity of beech and oak forests that come along with the rapid developments in information technology: It gives a comprehensive description of measured structural features of both species and evaluates and visualizes them with a branch-oriented polyhedra-based 3D-representation (CRISTO). This allows for the first time the proof of a naturally layered structure of Fagus sylvatica and Quercus petraea canopies, as well as the quantification of gap volumes of horizontal layers. The structure description is combined with the measured variability of physiologically relevant leaf parameters throughout the single canopies. A historical trend towards increasing leaf mass per area (LMA)-values is detected from literature. Using LMA and nitrogen content as drivers, a new nitrogen dependent leaf photosynthesis model is designed and validated from A/Ci curves and daily courses of leaf photosynthesis. These measurements have been perormed on standing trees using a high-lift. The program RACCIA allows for the automated derivation of photosynthesis parameters for this model from A/Ci-curves. Leaf properties and 3D-structure are used in the 3D-light model STANDFLUX-SECTORS, which is capble to use a 3D-simulation of the same stand in an unprecedented high resolution and was validated with the LMA-light relationship from another stand. The combined evaluation of the simulated radiation distribution with sapflow measurements on single branches indicates a typical pattern of light sensitivity of transpiration that is interpreted in terms of species-specific ecological specialization.
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