Fungal pathogens are increasingly recognized as an important source of adult-plant and seedling mortality in tropical forests, influencing tree demography, distributions, and diversity. However, very little is known regarding hidden effects of seed-infecting fungi, which influence seed survival. Seed-infecting fungi are likely to be especially important for tree species depending upon seed survival in soil (seed banks) for successful recruitment. We will undertake a detailed ecological and molecular characterization of seed-infecting fungi (endophytes, saprophytes, pathogens) associated with focal seed-bank-dependent tropical trees (Cecropia, Urticaceae) in three tropical forests (Costa Rica, Panama, Ecuador). Using field experiments, we will assess seed mortality attributable to fungi for 12 species, and the roles of local vs. foreign fungi in seed survival for three old-growth forest species. We will use molecular sequence data to identify fungi, and re-inoculation trials to assess pathogenicity of seed-infecting species. In so doing, we will test three primary hypotheses: (i) seed persistence in soil differs among tree species, reflecting differential susceptibility to fungal infection; (ii) tropical seed-infecting fungi are diverse and adapted to local hosts; (iii) nonpathogenic fungi protect seeds against disease.
This project promises a deeper understanding of factors underlying recruitment by a diverse and abundant group of tropical tree species, which in turn has important implications for management and restoration of forest ecosystems and maintenance of tropical biodiversity. Broader impacts include training for a doctoral student in field ecology and molecular techniques, improved collaborative links at an international level, and dissertation support and training for U.S., Ecuadorian, Panamanian and Costa Rican undergraduate students. We anticipate that this study will provide the first insights to the complexity of seed-fungal interactions in any natural system, and will provide much-needed training for young researchers in tropical molecular ecology.
