Population dynamics of soil microorganisms in termite mounds in Kenya

Abstract

The effect of termite activity on physical and chemical properties was examined in this study. Mainly the genus M. michelseni was investigated on six ’live' and six ’dead' mounds at a site belonging to International Centre for Insect Physiology and Ecology at Kajiado. A few other mounds were selected from Kibini, Emali, Magadi and Ruaraka. The soil analysis indicated that cation exchange capacity, calcium, magnesium and clay contents in the mound soil resembled those of the subsoil. The findings support earlier reports that the genus Macrtotermes uses the subsoil for mound construction. Carbon, clay, moisture contents and cation exchange capacity increased with depth of mound, attaining the highest levels in nursery and queen chambers of the ’open’ and ’closed' mounds. As a contrast to the adjacent soil profile, carbon content decreased with depth while clay and moisture content were almost uniform. Microbial activity measured as co2 evolution were studied in termite ’modified’ soils, sampled at varying distances of 0 m, 1 m, 3 m, 5 m, 10 m, 15 m and 20 *u respectively from the mound. Evolution of mg. C0o/g soil indicated that maximum microbial activity occurred between 3 - 10 m from the mound. The highest carbon content was measured in the same area. Dilution and plate count method was used to estimate the numbers of bacteria, fungi and actinomycete. A study of seasonal fluctuation of microbial population with respect to mound proximity showed that bacteria and fungi responded significantly (p 0.01) to seasonality. The highest bacterial counts corresponded to highest soil moisture content while fungi showed an opposite response to soil moisture. The population of actinomycete showed little or no response to both seasonality and mound proximity. In both ’open’ and 'closed' mounds built by M. subhyalinus and M. michelseni respectively, microbial populations were estimated in different chambers. ~ The three microbial groups namely, bacteria, fungi and actinomycete increased in depth of th^ mound towards the queen chamber. They then declined rapidly in the subsoil. In an adjacent soil profile the microbial populations depicted a significant negative correlation co-efficient (0.01) with depth. Different groups of bacteria were enumerated using most probable number technique (MPN). Soil samples were taken at 0 m, 3m, 20 m from the mounc to a depth of 13 cm. It was found that cellulose decomposers, denitrifiers, nitrifiers mainly Nitrobacter and Nitro- semonas sdp. were higher in the termite ’modified’ soils than in the surrounding top soil.. Using the MPN method the soil protozoa were shown to be mere numerous in the 'dead' than in the 'live' mound soils. It is suggested that cellulose decomposers and denitrifiers in the mound soils indicated presence of easily decomposable organic matter in the top soil. The high pH, Ca, Mg in the mound soil accounted for higher population of nitrifiers in the mound affected soils than in the surrounding soil. The moisture content was shown to influence bacterial and fungal numbers. Therefore during the dry season fungi and to a lesser extent actinomycete were major organic matter decomposers, while at the period of high soil moisture content bacterial activity was most important. Although activity of microorganism was shown to increase in termite modified soils, an indication of improved soil fertility, the foraging habits of termites might outweigh their use-fulness of improving soil physical and chemical properties .