Response of major soil decomposers to landslide disturbance in a Puerto Rican rainforest

To understand the relationship between soil biota and soil disturbance, we sampled an upper and a lower transect within each of two landslides and their adjoining forests, during both the wet and dry season in Puerto Rico. We found that the distribution of earthworms and soil microbes (e.g., fungi and bacteria) showed considerable spatial difference in these tropical landslides. We also found that endogenic earthworms (Pontoscolex corethrurus) occurred in all habitats (upper landslide 9.5 +/- 4 No. m(-2), lower landslide 43.8 +/- 11 No. m(-2), upper forest 35.7 +/- 8 No. m(-2), and lower forest 30.5 +/- 14 No. m(-2)), but anecic earthworms (Amynthas rodericensis) were only found in the undisturbed forests (3.4 +/- 0.6 No. m(-2)). Total bacterial and fungal biomasses were significantly higher in the forests than in the landslides. Active bacterial and fungal biomasses were significantly higher in the lower landslide area than in the upper landslide area. For all sampled soil parameters there was a dominance of microsite variation within landslides compared with seasonal changes or differences between landslides and adjacent forests. Earthworm density and biomass correlated positively with leaf litter, light-carbon fraction, and total bacteria and negatively with fine roots, suggesting that earthworm abundance and composition in landslides were regulated by carbon pools. Earthworm abundance and community structure as well as active and total fungal and bacterial biomass may reflect soil disturbance history and soil development processes over geological time in the Puerto Rican rainforest.