Microflora distributions in quaternary paleosols on Mount Kenya, East Africa

Abstract

When numbers of microorganisms in profiles of ground and buried soils on Mount Kenya were estimated by plate counting they were found to be consistently lower than those observed for other soils in different geographical regions. Numbers declined successively in deeper horizons and no evidence was obtained of irregular patterns of distribution controlled by soil forming processes, as observed frequently in certain Mollisols and Spodosols. The lower numbers and patterns of vertical distribution appear characteristic of younger Inceptisols and Entisols usually found in the alpine zone, and older Alfisols located in the Bamboo Forest region of Mount Kenya. The A horizons of the soils studied contain proportionately fewer of the total number of organisms in the A, B and C horizons than are observed in most soils. Estimates of organic matter suggest that this may be limiting since profile TV4a, with the highest counts, also had the highest organic matter content. However, extreme climatic conditions, such as severe drought and diurnal frosts, or unknown soil parameters, may also regulate the numbers of micro- and macroorganisms. Organic and inorganic horizons of buried soils often exhibit higher counts of micro-organisms than adjacent horizons of ground soils. However, bacteria and fungi do not appear to differ qualitatively from those in surface horizons. Taken in conjunction with other evidence obtained from the profiles we conclude that they are not indigenous, but introduced by root systems, or by upward movement of the water table contaminated with microorganisms. This appears to provide a means of determining which buried horizons are likely to be contaminated by biogeochemical processes, thus possibly affecting their radiocarbon ages.