Genetische Vielfalt und Vernetzung verschiedener Teilpopulationen von Corylus avellana L. und Prunus spinosa L. an Wald- und Wegrändern des Sollings

Abstract

During the last decades the increasing destruction of habitats by human beings has grown to a global problem. This can lead to displacements of populations or even fast eliminations of species as it is known for many examples in tropical forests. In the Central European cultivated landscape many animal and plant species are endangered especially by the increasing fragmentation of their habitats. The interruption of sexual contacts is followed by a decreasing genetic variation within populations. Today the genetic (intraspecific) variation is seen as the basis for the potential for adaptation and the long-term survival of populations. Therefore the possession of many genetic variants is important for tree and shrub species also with regard to the expected global climatic change in future.In this study, the genetic variation of the two shrub species Corylus avellana L. and Prunus spinosa L. common for Central Europe was investigated within and between different subpopulations in the Solling forest in North Germany by means of genotypic and phenotypic characters. Morphological parameters of leaves and height growth of cultivated offsprings were measured under homogenous site conditions. Morphological investigations on fruits were made in in-situ-populations of both species. Phenological characteristics of different offsprings were observed during flushing and bud set under constant climatic conditions. The analysis of vegetative reproduction, flowering and fructification of P. spinosa should give information about its reproductive strategies. The genetic structures of the in-situ-populations and their offsprings were analysed by Isoenzyme markers. Furthermore it was tested if there is a genetic exchange between separated individuals at the edges of forest and adjacent agricultural areas and if there are differences between wind-pollinated and insect-pollinated species. In addition, eclectors for trapping pollinators were installed at different sites in the study area during the flowering period of P. spinosa.The results of the inventory showed that compared to C. avellana P. spinosa is rare at the edges of the Solling forest but it can establish more often in the fields. In both species the morphology of the fruits was very variable and some parameters even varied multiple. For P. spinosa the variability of the fruits was especially determined by the different characteristics of the stones. The leaf morphology of the offsprings showed a high variability in size and shape for P. spinosa as well as for C. avellana. The biggest part of the evaluated variance of morphological fruit and leaf traits was caused up to 95% by the variation within the populations. But there were still some significant differences between the two provenances Vahle and Hellental. The height growth showed a strong differentiation between some individuals within the offsprings of P. spinosa. When comparing the two provenances of both species, the provenance of the climatically more favourable site Vahle had a better growth in the first two years on average. The results of the phenological observations tend to a later beginning of germination, a later flushing and an earlier bud set of the provenance of the climatically less favourable site Hellental for both C. avellana and P. spinosa. The span between early and late flushing and bud set respectively reached up to three weeks between different offsprings of P. spinosa. The mean growing seasons of offsprings varied in a span of 34 days. In the in-situ-population Hellental the time of flowering of P. spinosa started six days on average later than in Vahle. At the same location there was a difference of 15 days in the peak level of flowering.The allelic variation at isozyme gene loci demonstrated a low differentiation between the populations of both study areas for C. avellana and P. spinosa. Within one area some genetic variants were not detectable at the edges of forest, others were missing in the neighbouring fields. The Isoenzyme analysis of the offsprings illustrated a quantitative decrease of rare alleles which sometimes led to their complete disappearance. The pollinators of P. spinosa seemed to be locally differentiated. Altogether the results indicated a restricted gene flow especially for P. spinosa. While the differentiation in flowering and fruit morphology of the in-situ-populations is probably to a large part environmentally influenced, the variation of different morphological and phenological characteristics of the offsprings cultivated under homogenous site factors is due to genetically differences.The great variability of the analysed parameters suggests a high potential for adaptation of the populations in the study area. With the example of P. spinosa the present results make clear, that the genetic variation of insect-pollinated species with low abundance in a fragmented landscape and predominant dispersal by birds is endangered by a restricted gene flow and less probabilities for seedlings to become established. The genetic variation of wind-pollinated species with a high abundance and a predominant dispersal by mice showed, considering C. avellana as example, a lower endangering.