Occurrence and Distribution of Soil Organisms I. Geographical distribution A. Isolates of almost all taxa can be found in your backyard B. Worldwide distribution due to transport via wind, aerosols, dust particles, in ocean currents, precipitation, by animals. D. However in general, similar soil biota are found in similar environments, regardless of geographical location.
Older studies indicate that microbial numbers generally decrease with depth in soil profile.
Also certain groups drop off and activity of populations decrease with depth. Older studies used rich nutrient medium that selects for eutrophs. Recent studies using lower nutrient levels suggest that populations in subsurface are sometimes equal to, although frequently slightly lower than, those in soil. Numbers are much more variable in subsurface than soil, suggesting much greater spatial variablility. B. Soil matrix 1.