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Pathogens and seed mortality in neotropical soils.
Gallery, Rachel*,1, Dalling, James1, 1 University of Illinois Urbana-Champaign, Urbana, IL
ABSTRACT- Successful recruitment for many light demanding tree species is dependent upon seed survival in the soil seed-bank. Seed-bank experiments conducted to date implicate soil-borne fungi as predominant mortality agents of small-seeded tropical tree species. To investigate the sources of variation in seed susceptibility to pathogenic fungi, we conducted reciprocal transplant experiments between populations of common light demanding tree species in lowland Neotropical forests. Seeds were collected from individuals of five species from La Selva Biological Station, Costa Rica, and at Barro Colorado Island (BCI), Panama and incubated in the soil for five months. We have found that: (1) fungi significantly limit survival in the soil-seed bank for these species; fungicide experiments at both sites increased seed survival by 28-50% (2)overall seed mortality is significantly higher at La Selva than at BCI (F=49.0, df=1, p<.0001), and (3) higher seed mortality for one species, Cecropia insignis (Cecropiaceae), buried beneath conspecific versus heterospecific crowns (F=28.53, df= 1, P <.0001). We also found evidence for differences in seed survival among individuals, meaning seed source and burial location contributed significant variation to overall seed mortality. These results indicate the potential for host-specificity of soil-borne fungi in this system, which could influence local species composition through host-specific recruitment limitation. These preliminary results suggest that sources of variation in fungal-mediated seed mortality are evident across multiple scales.
Key words: tropical, soil-seed bank, recruitment