Observations On The Ecology Of Earthworms And Its Effect On The Population Dynamics Of Cellulolytic Bacteria In Soils Across Selected Habitats In Imo State University Main Campus Owerri, Nigeria

Abstract

This study was aimed at investigating the relationship between the population dynamics of earthworms and the populations of total and cellulolytic bacteria in the soil across selected sites within the Imo State University main Campus Owerri, Nigeria. Four habitats, namely, land with trees and grass cover, lawn with total grass cover, lawn with scanty grass cover and abandoned farmland where selected and composite soil samples were collected from them. After analyzing some physico-chemical properties of soil samples, the total number of bacteria in nutrient-agar and aerobic cellulolytic bacteria in cellulose-agar were counted. Assessment of bacterial cellulolytic activity was performed via measurement of clear zone around of colony. Also, earthworms were collected from the study sites and their population density, biomass, length, proportion of adults and juveniles and taxonomic features were compared among the four habitats. Result showed that the land with trees and grass cover recorded the highest total bacteria, aerobic cellulolytic bacteria, proportion of cellulolytic bacteria, worm density, worm biomass, and worm length (241.4x10 4 cfu/g, 123.8x10 4 cfu/g, 51.28%, 37.5+10.8m -2 , 5.2+2.1gm -2 and 20.4+8.1cm), followed by the lawn with total grass cover (203.6x10 4 cfu/g, 96.8x10 4 cfu/g, 47.54%, 23.5+6.4m -2 , 3.3+1.8gm -2 and 13.4+6.2cm), the lawn with scanty grass cover (127.3x10 4 cfu/g, 34.7x10 4 cfu/g, 27.26%, 16.7+5.3m -2 , 2.3+0.5gm -2 and 11.9+2.3cm) and the abandoned farmland (106x10 4 cfu/g, 23.8x10 4 cfu/g, 22.37%, 11.8+4.4m -2 , 1.6+0.3gm -2 and 12.8+3.1cm). Mean ratio of clear zone diameter to colony were 1.60+0.42, 1.3+0.36, 0.8+0.22 and 1.93+0.25 for the land with trees and grass cover, the lawn with total grass cover, the lawn with scanty grass cover and the abandoned farmland, respectively. Higher ability of the cellulolytic bacteria in the abandoned farmland and the land with trees and grass cover may be due to species diversity. All four habitats had a higher proportion of adult earthworms than juvenile earthworms in an approximate ratio of 3:1, adult: juvenile. Finally, the taxonomic status of the earthworms in all four habitats suggested that they may belong to the same species. However, species identification was not attempted.