The distribution and abundance of soil nematodes in East African savannas

Abstract

Nematodes were sampled from sites under and between tree canopies in Tsavo National Park, Kenya. We tested the hypothesis that more nematodes would be present in the generally moister soil, under the canopy, with a larger biomass of green grass prevailing for many months of the year. We found that microbivorous nematodes comprised the bulk of the populations, approximately 90% of the total. Bacterivores were more numerous (approximately 3×105 on average) versus fungivores (approximately 5×104 on average) per m2, to 10 cm depth. All four trophic groups (plant parasites and omnivore/predators in addition to the microbivore groups mentioned above) were significantly higher under acacia than baobab in a drier site, but not significantly different under the two tree species in a wetter site. Only bacterivores were significantly different with respect to distance from the tree, with higher numbers associated with the higher microbial biomasses under the tree canopies. These higher microbial biomasses were reflected in 2.5 times more potentially mineralizable N under the tree canopies at the drier site. We suggest that belowground detrital and microbivorous food webs in savannas may be similar to those in temperate grasslands. Further proof of this idea awaits more extensive research.