The fumigation-extraction method was used for measuring soil microbial biomass of C (BM-C) and N (BM-N) in a red-yellow latosol under different forest types. Soil samples from eucalypt and pine plantations presented higher values of BM-C (223.72 and 207.39 mg kg-1 of C in the soil, respectively) than samples from Piptadenia rigida and regenerating secondary forest (82.94 and 79.47 mg kg-1 of C in the soil, respectively). Similar results were obtained for the litter layer. On the other hand, the rate of the specific respiration of microbial biomass (TR-BM) was the highest in soil samples collected from the Piptadenia rigida plantation and regenerating secondary forest. The BM-N ranged from 8.05 to 16.08 mg kg-1 of N in the soil. The TR-BM was negatively correlated with soil nitrogen content (r = -0.76**) and with the amount of litter layer (r = -0.68*). The BM-N was also negatively correlated with the nitrogen content of the litter layer (r = -0.52*) and with soil mineral nitrogen content (r = -0.71*). BM-C, BM-N and respiration rate (RR) were positively correlated with soil organic carbon content (r = 0.63*, r = 0.71* and r = 0.76*, respectively). Soil nitrogen content showed significant positive correlation with BM-C and RR (r = 0.77* and r = 0.60* respectively). The results showed that BM-C and BM-N associated to soil organic carbon, soil total-N and TR-BM are sensitive indicators of the dynamics of these elements in the soil, indicating the lower potential of organic matter decomposition in soils under eucalypt and pine.
microbial biomass; soil respiration; fumigation-extraction; mineral nitrogen