The effect of converting tropical native savanna to Eucalyptus grandis forest on soil microbial biomass

The aim of this work was to investigate the effect of converting native savanna to Eucalyptus grandis forest on soil microbial biomass in tropics. Soil samples were collected from three sites: undisturbed native savanna (savanna), the site of a 1-year-old E. grandis forest (1 y), and the site of a 2-year-old E. grandis forest (2 y). Soil microbial biomass C (MBC), basal respiration, substrate induced respiration (SIR), soil organic carbon (SOC), microbial, and respiratory quotients were evaluated in soil samples collected from 0–20 cm depth. One year converted forest caused a significant reduction in MBC, SIR, and microbial quotient (about 70, 65 and 75 per cent, respectively). However, after 2 years of E. grandis forest growth, there was recovery of these variables. Soil basal respiration and respiratory quotient were significantly higher in 1 y forest (about 4 and 14 times, respectively) than in savanna. The results showed a significant decrease, after 2 years, in soil respiration and respiratory quotient, suggesting a recovery of soil microorganisms as time passes. In the short term, our results showed negative changes in soil microbial biomass following the conversion of native savanna to E. grandis. Copyright © 2010 John Wiley & Sons, Ltd.