Monday, August 2, 2010

PS 13-104: Environmental vs. genetically-based foliar traits and resistance to herbivores in Patagonian southern beeches

Lucas A. Garibaldi1, Enrique J. Chaneton2, Thomas Kitzberger1, and C. Noemí Mazía3. (1) CONICET - Universidad Nacional del Comahue, (2) IFEVA - Facultad de Agronomía, Universidad de Buenos Aires, (3) Facultad de Agronomía


Spatial environmental heterogeneity can drive different plant syndromes within the habitat of one species. Tree species forming natural monospecific stands along wide habitat distribution, such us the southern beech Nothofagus pumilio, can be useful to understand the influence of abiotic and biotic factors on constitutive plant traits and genotypic × environmental interactions without the confounding effects of plant species composition changes among sites.

Our objectives were to: 1) identify plant constitutive syndromes in terms of growth rates, leaf phenology, and leaf traits; 2) evaluate the association between these syndromes and the characteristics of their site of origin (precipitation, temperature, and folivory); 3) understand the consequences of these syndromes on plant survival and resistance to herbivory in contrasting environments. We collected juvenile plants (c.a. 30cm high) originated from six different environments in terms of precipitation, temperature, and herbivory within N. pumilio monospecific forests of northern Patagonia (Argentina). Each population was planted at two contrasting sites, one dry and warm forest (40º36’S, 71º05’W, annual precipitation: 1150mm year-1) with high abundance of insect folivores and mammals herbivores, and one wet and cold forest (40º37’S, 71º50’W, 2750mm year-1) with low abundance of both types of herbivores. In each plant, we measured survival, growth, leaf phenology, leaf size, leaf toughness, leaf density of trichomes, folivory by different insect guilds, and browsing by mammals.


We found differences in plant syndromes associated to the annual precipitation and mean temperature of the site of origin. At both contrasting planting sites, the three populations originated from drier and warmer forests showed lower trichome density, smaller leaf size, and earlier bud breaking and leaf expansion than the three origins from wetter and colder forests. All origins showed earlier leaf phenology and higher leaf toughness when planted in the dry/warm forest compared to the wet/cold forest, but we found no difference between forest sites in trichome density. In general, folivory received by each plant population was negatively associated with the mean annual precipitation of the site of origin, and positively associated with mean temperature. Plant populations did not differ in survival so far, but all origins showed lower survival in the dry/warm forest site. Our results suggest that trichome density is under genetic control, showing no plastic responses to contrasting environmental conditions. We conclude that N. pumilio populations show constitutive traits associated with climatic conditions of the site of origin that provide differential resistance to herbivory.