The effects of Eucalyptus globulus Labill. leaf letter on C and N mineralization in soils from pasture and native forest

The effects of addition of Eucalyptus globulus leaf litter on carbon and ni trogen mineralization in soils from a pasture and a native forest were eval uated using a long-term laboratory aerobic incubation assay (29 weeks at 20 degrees C) in leaching microlysimeters, The amount of added leaf litter si gnificantly influenced microbial respiration, microbial biomass and N turno ver in both the native forest and pasture soils. Cumulative CO2-C respired increased with increasing rate of leaf litter addition when leaf litter was mixed through the soil or placed on the soil surface. These increases were associated with increases in microbial biomass C content. Cumulative net N mineralization declined in ail treatments when litter was added and was lo west when leaf litter was mixed with soil. When leaf litter was added in in creasing amounts to the soil surface, there was a concomitant increase in m icrobial biomass N content (r(2) = 0.79, n = 8), indicating that the reduct ion in net N mineralization was primarily due to immobilization of N in mic robial tissues. In contrast, when litter was mixed with soil in increasing amounts, there was a decrease in microbial biomass N in forest soil and an increase in pasture soil. Consequently, changes in the rate of net N minera lization were not well related to changes in microbial biomass N content. I t is suggested that this may be due to the greater activity and more rapid turnover of microorganisms where litter was incorporated resulting in more of the immobilized N being partitioned into metabolic products or dead micr obial cells. Incorporation of litter may also have enhanced loss N through denitrification, (C) 1999 Published by Elsevier Science Ltd. All rights res erved.