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Silver birch leaves.

Intraspecific variation in silver birch leaf spectral reflectance and surface secondary metabolites

Natural variation within a species facilitates adaptation to changing environment. In this study, variation in silver birch leaves due to the genotype and provenance of origin on the spectral reflectance, ecophysiological leaf traits, surface secondary metabolites and their relation to  herbivore resistance are reported. Thus, this study gives insights into the inherited genetic diversity of silver birch. 

Leaf spectral reflectance varied more prominently by provenance and secondary metabolites by genotype. The chlorophyll content showed clear provenance variation and the discrimination of genotypes and provenances were influenced by it and related spectral features around the red edge of the reflectance spectrum. Both study years showed similar patterns of variation in spectral profile and chlorophyll content. These results and the consistent patterns of genotype-related leaf surface secondary metabolite abundances indicate a strong genetic influence on the optical properties of silver birch leaves, foliar chlorophyll content, and secondary metabolite accumulation. The secondary metabolite contents of the leaves were associated with foliar herbivory, in line with their likely role in chemical defense of the trees to insect herbivores. The provenance-related variation in all of these traits may also reflect adaptive differences to environmental conditions among the sites of origin or differences in acclimation to the common garden site. 

There was also variation in spectral reflectance within silver birch trees so that the leaves on the upper and lower parts differed clearly from each other. Other leaf traits, such as chlorophyll content and specific leaf area showed also significant variation within the tree crown. The results imply that within-tree variation should be taken into account in studies on tree spectral reflectance and designing representative leaf sampling for research. 

Boreal forest comprises 30% of the global forest area and boreal forest are undergoing extensive climate change. It is essential to understand the genetic diversity. In this study, genetic difference in the silver birch tree leaves, originating from southern, central and northern parts of Finland and growing in a common garden study in central Finland (Joensuu Botanical garden) were investigated. 

The doctoral dissertation of MSc Maya Deepak, entitled Intraspecific variation in silver birch leaf spectral reflectance and surface secondary metabolites will be examined at the Faculty of Science and Forestry o the 15th of December online. The opponent in the public examination will be University Researcher, Docent Matthew Robson, University of Helsinki, and the custos will be Professor Elina Oksanen, University of Eastern Finland. The public examination will be held in English.

Link to the event

Link to the dissertation