Erdbeerbäume

Die kugeligen, rot-orange gefärbten Früchte der Erdbeerbäume (Arbutus) erinnern auf den ersten Blick an Erdbeeren, haben aber weder geschmacklich noch anatomisch oder systematisch etwas mit diesen gemein. In der Neuen sowie der Alten Welt gibt es insgesamt 11 Arbutus-Arten, die vor allem im Mittelmeerraum und Mexiko vorkommen. Es handelt sich um immergrüne Sträucher und Bäume mit meist auffällig roter Rinde, die sich schuppenartig vom Stamm löst. Im Palmengarten vertreten sind recht große Exemplare des Amerikanischen Erdbeerbaums (Arbutus menziesii) und des Westlichen Erdbeerbaums (Arbutus unedo).

Genetic structure and mating system of northern Arbutus menziesii (Ericaceae) populations

Arbutus ( Arbutus menziesii Pursh. (Ericaceae)) is the only broadleaved evergreen tree native to Canada. It occurs in three red-listed (endangered) plant communities in British Columbia (BC), threatened by urban encroachment, fire suppression, grazing, and exotic invasive species. Its growth is sensitive to environmental changes: more severe summer drought caused by climate change could further threaten this species. Amplified fragment length polymorphisms (AFLPs) were assayed in 10 populations in BC and 1 in Washington to obtain baseline population genetic and mating system data. We found that genetic diversity within populations was low (mean H = 0.094) for a woody perennial. Genetic variation among populations (FST = 0.15) was comparable to woody perennials on average (0.19). Pairwise kinship coefficients were significantly associated with distance (p < 0.01). The multilocus outcrossing rate for one BC island population was high (tm = 0.97), but inbreeding due to consanguineous matings was also quite high (tm – ts = 0.10). These data can be used to guide conservation strategies and future research priorities for arbutus.

Diversity and host specificity of ectomycorrhizal fungi retrieved from three adjacent forest sites by five host species

Seedlings of Abies grandis (Dougl.) Lindl. (grand fir), Lithocarpus densiflora (Hook. & Arn.) Rehd. (tanoak), Pinus ponderosa Dougl. ex Laws. (ponderosa pine), Pseudotsuga menziesii (Mirb.) Franco (Douglas-fir), and Arbutus menziesii Pursh (madrone) were planted in mixture and monoculture in soil collected from three adjacent forest sites in southwestern Oregon (a clearcut area, a 25-year-old Douglas-fir plantation, and a mature 90- to 160-year-old Douglas-fir - pine forest) to determine the effect of host tree diversity on retrieval of ectomycorrhizal morphotypes. In this greenhouse bioassay, 18 morphotypes of mycorrhizae were recognized overall from all soils with a total of 55 host-fungus combinations: 14 types with ponderosa pine, 14 with Douglas-fir, 10 with tanoak, 10 with grand fir, and 7 for madrone. Four genus-specific morphotypes were retrieved (three on ponderosa pine and one on Douglas-fir), even in mixture situations, demonstrating selectivity of some fungal propagules by their respective host. Five types were detected on all hosts, but not necessarily in soils from all sites. The remaining nine types were associated with two, three, or four hosts, which indicates a wide potential for interspecific hyphal linkages between trees. More morphotypes were retrieved from the monoculture treatments compared with the mixture treatments, although the differences were not significant. Several examples of acropetal replacement of one fungus by another (interpreted as succession) were recorded on all hosts during the course of the experiment. These results illustrate the importance of different host species in maintaining ectomycorrhizal fungus diversity, especially fungi with restricted host range, and the strong potential for fungal linkages between trees in forest ecosystems.Key words: fungal succession, fungal communities, compatibility, Arbutus menziesii, Pseudotsuga menziesii, Pinus ponderosa, Abies grandis, Lithocarpus densiflora.