Document: ADL-3-58-35

What is the extent of niche diversity in soil protozoa?

ADL, S.M.* and D.C.COLEMAN

Institute of Ecology, University of Georgia, Athens GA 30602-0002 USA ¹

Abstract:
Soil protozoa species diversity can be in the hundreds for a few grams of soil. A considerable number of species are ubiquitous and common in most soils. This tremendous diversity of biochemical and ecological function is theoretically sustainable because of niche separation in time and space through the soil. But it is unclear to what extent this niche separation exists. Some argue that there is considerable niche overlap and protozoa are best grouped into broad functional groups. In general the literature tends to represent the protozoa grouped by size or locomotion. To estimate the extent of niche separation in natural systems, three sets of experiments were conducted. The first was an assay of the mobility of a soil protozoa assemblage, using 15 by 2 cm soil columns under various abiotic conditions, with varied soil types. Migration through each column resembled chromatography for chemical separation. Here protozoa were separated by their mobility against an abiotic gradient. Increasing clay content inhibited proliferation and mobility. The second set of experiments consisted of 75 cm holes dug in an agricultural field and in a more heterogeneous forest soil. Each experimental hole was re-filled with autoclaved soil or sand (free of organic matter) with different litter additions, and plots were kept free of new roots or litter. Control plots contained soil that was dug out and returned. Re-colonisation of the plots by protozoa was monitored monthly. These results distinguished early colonisers from later successional species, as distinct from fast moving species. Treatments with different litter types (representing various decay rates and nutritional parameters) promoted distinct re-colonisation patterns. Lastly, we investigated 3g soil microcosms supplemented with a variety of powdered leaf litter, in a range of moisture content and temperature fluctuations. Each treatment promoted a distinct succession pattern over 1-6 weeks, as the nutrients were used up. Later stages promoted a variety of less common species. Conclusions from these lend support to the emergence in succession, of abiotic and biotic conditions, promoted by fluctuations in temperature and moisture, which promote particular species. Osmotrophy as well as bacterivory must be considered to appreciate the extent of niche separation in flagellates.

Keywords: soil protozoa, diversity, succession, colonisation

This abstract is being presented at: 8:30 AM in session:
Oral Session #23: Soil Ecology.