Tannenmistel versus Kiefernmistel: ein morphologisch-ernährungskundlicher Vergleich

The white-berry mistletoe (Viscum album L.), which is spreading more rapidly among silver fir (Abies alba Mill.) and Scots pine (Pinus sylvestris L.) as a result of climate change, is playing an increasingly important role in the forests of Bavaria, as its infestation is causing growth losses and rising mortality rates in the trees. The aim of this study was to determine the behaviour of mistletoe affecting fir (Viscum album spp. abietis (WIESB.) JANCH.) and pine (Viscum album spp. austriacum, (WIESB.) VOLLM.) trees on sites with different degrees of base saturation, as well as to compare both mistletoe subspecies directly with each other. Furthermore, an influence of mistletoe infestation on the needles' nutrient levels and morphological parameters (100-needle-weight, needle-length and shoot-length) of fir and pine trees on the different sites was described. For this purpose, three sites with different base saturation level were selected per tree species. Five trees were sampled per site. Three branches were sampled per tree: two branches with mistletoe and one branch without mistletoe as reference. These branches were divided according to needle age groups. Afterwards, the morphological parameters were recorded and the needles were analysed in the laboratory in order to obtain their nutrient content. The mistletoe was also broken down separately according to its components (leaves and shoots of different age) and analysed in the laboratory. The mistletoe does not show a uniform nutrient element level across the sites; rather, the mistletoe adapts its nutrient supply to the conditions of its host and thus of the sites. Conversely, this means that mistletoe has no distinct regulatory abilities to decouple its nutrient regime from that of the host. There are also clear differences in the nutrient content of mistletoe leaves and shoots, and a decrease in nutrient content with increasing age of the shoots. The values also indicate that the two mistletoe subspecies should be considered separately, as they in part have considerably different nutrient contents. While with increasing mistletoe biomass in pine no significant effects on the needles beyond the mistletoe infestation could be detected, fir reacts much more sensitively. Here mistletoe causes a significant reduction in shoot length and in the P, S and K content of the needles with increasing age and thus increasing size. Thus, nutrient deprivation by mistletoe, at least in silver fir, represents an additional risk factor, in addition to the increased drought stress caused by its water consumption.