Leaf litter decomposition in a tropical peat swamp forest in Peninsular Malaysia

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It has long been assumed that the peat underlying tropical peat swamp forests accumulates because the extreme conditions (water logged, nutrient poor, anaerobic and acidic—pH 2.9-3.5) impede microbial activity. Litterbag studies in a tropical Malaysian peat swamp (North Selangor peat swamp forest) showed that although the sclerophyllous, toxic leaves of endemic peat forest plants (Macaranga pruinosa, Campnosperma coriaceum, Pandanus atrocarpus, Stenochlaena palustris) were barely decomposed by bacteria and fungi (decay rates of only 0.0006-0.0016 k day-1), leaves of M. tanarius, a secondary forest species were almost completely decomposed (decay rates of 0.0047-0.005 k day-1) after 1 year. Thus it is intrinsic properties of the leaves (that are adaptations to deter herbivory in the nutrient poor environment) that impede microbial breakdown. The water of the peat swamp was very high in dissolved organic carbon (70-84 mg l-1 DOC). Laboratory studies revealed initial rapid leaching of DOC from leaves (up to 1,720 mg l-1 from 4 g of leaves in 7 days), but the DOC levels then fell rapidly. The leaching of DOC resulted in weight loss but the physical structure of the leaves remained intact. It is suggested that the DOC is used as a substrate for microbial growth hence lowering the concentration of DOC in the water and transferring energy from the leaves to other trophic levels. This would explain how nutrient poor tropical peatswamps support diverse, abundant flora and fauna despite low nutrient levels and lack of rapid litter cycling such as occurs in other types of tropical rainforests.

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