GUADARRAMA, PATRICIA C. & JAVIER F. ALVAREZ-SANCHEZ.
Universidad Nacional Autonoma de Mexico, MEXICO.
Earlier pioneer species modify environmental conditions and soil resources. Due to their ability to facilitate the development of mycorrhizae, mid and late-successional species can establish later in time. The objective of this study was to analyze the effects of mycorrhizal fungi regarding the growth and survival, and to assess the importance of mycorrhizal colonization on the competition between seedlings of an early pioneer species (Heliocarpus appendiculatus) and a late pioneer species (Stemmadennia donnell-smithii) in a tropical rain forest in Mexico. These species coexist in gaps, edges and riparian corridors. Two growing experimental conditions were used: in presence of a neighbor of the same species and of a neighbor of different species, with and without mycorrhizae inoculum. An ANOVA test was used to analyze the dry weight; survival curves were analyzed with Peto and Peto test while competition intensity was analyzed with Wilson and Tilman test. H. appendiculatus does not need mycorrhizal fungi for growth and survival, but this association helps in competition conditions. S. donnell-smithii improves growth, survival and competition with mycorrhizal fungi. We conclude that plant life histories and the association with mycorrhizal fungi modify competition among plants.