MICROBIAL RESPIRATION AND NITROGEN RELEASE PATTERNS OF DECOMPOSING <em>ACACIA</em> <em>MANGIUM</em> LEAF LITTER FROM KEMASUL FOREST RESERVE, MALAYSIA

Abstract

Decomposition trials under laboratory and field conditions with Acacia mangium leaf litter were made over a period of 140 days and several possible factors influencing this process were examined. Resource quality of A. mangium litter varied significantly between plant ages (12, 18 and 24 months) at young stand. The nitrogen content in the leaf litter was lowest at the 18-month-old stand, corresponding to the lower nitrogen concentration in the green leaves. Organic carbon was quite constant while litter production was highest in the drier period. The percentage of polyphenols decreased with increasing age, hemicellulose content remained constant and cellulose increased with the age of plantation. The addition of this litter to the soil enhanced the microbial respiration, measured as the rate of CO₂ evolution under laboratory condition. The pattern of CO₂ release proceeded through two phases, an initial rapid release followed by a slow release. This microbial activity resulted in immobilisation of mineral nitrogen in the litter and mineralisation in the soil. Release of mineral N from decomposing A. mangium litter under field condition followed three phases, i.e. leaching, immobilisation and mineralisation. The leaching period was rather short, producing a release of soluble nitrogen.