Variation of microbial community along a chronosequence of age in Eucalyptus grandis forest plantation and some other land uses in the intermediate zone of Sri Lanka

Abstract

Population variation of fungi and bacteria in different aged Eucalyptus grandis plantation forest soil was studied. Plantations aged 7, 13, 22 and 30 years and adjacent tea estate, abandon Eucalyptus planted site (without plants) and natural forest were selected as study sites from Passara, Uva Province area. Necessary parameters were considered to minimize microclimatic variations among the field sites. Soils were collected using a soil auger cleaned with 90 % alcohol from top layer (0-15 cm layer). The soil extractions were prepared in dilution series and cultured using Potato dextrose agar and nutrient agar and microbial count was taken. Eucalyptus plantations showed lower amount of fungal populations compared to other sites. The 30 years old Eucalyptus plantation had the highest amount of fungal population (953±122 MPN g -1 ) compared to other Eucalyptus plantations. There were significant relationship between fungal population and stand age of Eucalyptus plantation (p<0.0001; R2 = 98.44 %). But the stand age is not significantly affected to bacterial population (p > 0.05). So mainly because of fungal population, fungi to bacteria ratio (F: B) in soil varied with plantation‟s stand age. The low F : B indicated that Eucalyptus plantation forests are bacteria dominant. This study suggest that fungal population is more sensitive than bacterial population to the stand age related factors in soil such as nutrient content and understory, which could be important in sustainable management and restoration of Eucalyptus plantation soils for a better yield.