ECTOMYCORRHIZAS ... DOES AGE MATTER?

FERNÁNDEZ NATALIA; FONTENLA SONIA; GALLO LEONARDO; MARCHELLI PAULA

Pucón, Chile

Simposio; 5th International Symposium of Interactions of Soil Minerals with Organic Components and Microorganisms (ISMOM); 2008

Soil microorganisms play a significant role in regulating ecosystem processes, ranging from nutrient cycling to plant health. Studies on the interactions between plants and rhizospheric microbes are important for understanding ecosystem dynamics and because it would be interesting to find out how these microorganisms could be used in agriculture and forestry management. Mycorrhizas are mutualistic associations between soil fungi and plant roots, and form a key component of soil microbial populations. They influence plant growth and nutrient uptake, and provide a greater area for interactions with other soil microbes. In temperate and boreal forests, the establishment, growth and survival of different tree species are usually dependent on colonization by ectomicorrhizas (ECM). Nothofagus nervosa (Raulí) is an ecologically and economically important species of South American temperate forests. In Argentina, this species has a reduced natural distribution area, in part due to its overexplotation in the past because of its high wood quality. This critical situation led to the implementation of conservation and domestication programs. Among the different aspects that should be considered in these programs are the ECM associated with this species, which are of great importance for plant growth and for their subsequent implantation in the field. The general aim of the project is to analyze the abundance and diversity of ECM in N. nervosa, to compare them between native and nursery cultivated individuals and finally to select some ECM strains which would have significant application in domestication processes. In this context, the starting point is the quantification and characterization of ECM in N. nervosa. Hence, the first step was to analyze the percentage of root tips colonized by ECM in N. nervosa individuals and to compare it among plants of different ages belonging to four categories: seedlings, young and old native individuals and young nursery cultivated individuals. During spring 2007, 5 trees of each category were randomly selected from a native forest and from a field trial established in this forest in Patagonia, Argentina. Seedlings with complete root systems were carefully removed with a shovel and the rest of the plants were sampled by taking 3 soil cores per tree. Samples were wrapped in plastic bags and stored at 4°C. Roots were sieved from the soil cores, carefully washed and then ECM were quantified. ECM were observed in every sample. At least 95% of the root tips examined per plant had formed ECM. There were no significant differences in the percentage of root tips colonized by ECM among the four analyzed plant categories or within each of them. These results agree with some authors which have suggested that the development of ECM do not depend on the age of the tree. It might be possible to find different ECM morphotypes in different plant categories, but this fact needs to be further studied. This work constitutes the first description of the influence of tree age on ECM colonization in a forest of Patagonia. Besides, this study constitutes the initial step in the analyses of ECM in N. nervosa and provides the basis for further investigations, such as the interactions of ECM with other soil microbes, their influence in plant fitness and their possible application in conservation and domestication programs.