Forests of the south: biogeographic history in complex landscapes

A.C. PREMOLI

Congreso; International Workshop: Mycorrhizal simbiosis in the southern cone of South America; 2017

The physical setting of Patagonia consists of heterogeneous landscapes along steep environmental gradients occurring even at short spatial distances. Trees and shrubs of subgenus Nothofagus are widely distributed in Patagonia and were used to analyze variations in the physical environment along different time scales that affect their genetic makeup and thus to study past, present, and future evolutionary potential. We combined distinct molecular markers as well as modeling and experimental approaches. Conserved DNA sequences of the chloroplast (cpDNA) were used to analyze past responses related to the influence of geologic forces in all five species of the subgenus: the evergreen Nothofagus betuloides, N. dombeyi, and N. nitida and the deciduous N. antarctica and N. pumilio. They are commonly found in pure stands although they can also coexist in sympatry/parapatry where hybrids can be produced. Concordant geographic cpDNA patterns suggested a shared evolutionary history maintained by cycles of hybridization/introgression. Variation in biparentally inherited markers on the two widespread most deciduous species, yet ecologically distinct, showed that the habitat restricted N. pumilio yielded an impoverished gene pool probably related to genetic bottlenecks suffered along its range. This is in contrast to the high genetic diversity found in the N. antarctica that inhabits diverse habitat types. Ecological genetic studies showed that the spatial distribution of genotypes at short spatial scales depended on the regeneration strategy of species (seeders vs. resprouters) and type of disturbance, postfire stands yielded a more homogeneous genetic structure while mature stands undergoing gap-phase regeneration were genetically structured. Common garden and reciprocal transplant experiments of N. pumilio from contrasting elevations showed that ecomorphological traits have a genetic basis which may limit potential responses under climate change. The southern tip of South America varies in climates and history that result in a combination of adaptive and plastic responses of plants.