Progress in phenological modelling on the basis of metabolomic approaches

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Modelling of phenological stages, such as the flowering of fruit trees, is based on temperature sums for many decades, describing both the chilling and the forcing requirements of woody plants until the beginning of flowering. These approaches go back to Reaumur (1735), who originally proposed the concept of Growing Degree Days. Recently, there is a growing body of opinion that asks for new methods in phenological modelling and more in-depth studies on the dormancy of woody plants. This requirement is easily understandable if we consider the wide application of phenological models, which even can affect the results of climate models.To this day in phenological models, still a number of parameters must be optimized on observations, although some basic physiological knowledge of the chilling and forcing requirement of plants is already considered (semi-mechanistic approaches). Limiting, for a fundamental improvement of these models, is the lack of knowledge about the course of dormancy in woody plants, which cannot be directly observed and which is also insufficiently described in the literature. Modern metabolomic methods provide a solution for this problem and allow both the exact validation of currently used phenological models as well as the development of new mechanistic approaches. For this reason it is necessary to track changes in the concentration of selected phytohormones (abscisic acid) and their precursors (carotenoids) in high temporal resolution, in order to replace the currently optimized dates for the release of dormancy and the beginning of ontogenetic development by analytical results. Furthermore, the context of free amino acids with dormancy and the subsequent growth and development processes of flower buds will be derived. For new phenological modelling approaches changes of these metabolites (concentration, temporal course) must be set in relation to the variability of environmental parameters (weather, day length, etc.). This necessarily requires multi-year and high-resolution data of the dependency of the relevant substances on controlling environmental parameters. These studies are now feasible, but scientifically not implemented, yet. The feasibility of this approach has already been tested in a 2-year pilot-study on sweet cherries and should be continued and intensified in the planned project. The suggested methodology is not only limited to the flowering of fruit trees, it can also be applied to tree species of the natural vegetation, where even greater deficits in phenological modelling exist.