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

Abstract

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.

Impact of Simulated Changes in Water Table Depth on Ex Situ Decomposition of Leaf Litter from a Neotropical Peatland

“…3 Response supports the view that litter properties are the overriding influence on decomposition (Enriquez et al 1993;Yule and Gomez 2009). However, as shown here, a lowering of the water table may increase mass loss in some litter types by c. 10 % over longer timescales (>15 months).…”

“…Importantly, although a substantial quantity of mass was lost from both C. panamensis and Cyperus sp. litters, decay rates were much lower than those observed in situ in Micronesia (Chimner and Ewel 2005;Yule and Gomez 2009), suggesting that variation in the lability of litter may strongly influence C sequestration in peat. However, it is plausible that higher in situ degradation rates are linked to the field environment (e.g.…”

“…The relative contributions of carbon to peatlands from fine litter, including leaves, coarse woody debris and roots are broadly similar, with fine litter input being marginally greater (Mahli et al 2011). Decomposition of leaf litter is important for the rapid return of nutrients to the ecosystem (Schreeg et al 2012) and may also make an important contribution to peat formation (Brady 1984;Yule and Gomez 2009).…”

“…Site conditions and litter quality, defined here as a combination of organic matter chemistry and nutrient concentration, are well established determinants of litter decomposition (Miyajima et al 1997;Rejmánková and Houdkova 2006;Guo et al 2008;Yule and Gomez 2009;Cheesman et al 2010). Thus, litter containing easily degradable material decomposes more rapidly than that from species containing more recalcitrant material (Kao et al 2003;de Neiff et al 2006;Crawford et al 2007).…”

“…Low nutrient concentrations in leaves may also limit decomposition rate (DeBusk and Reddy 2005;Rejmánkova and Sirova 2007;Fennessy et al 2008;Wang et al 2010). However, little is currently known regarding the influence of species composition and variation in site conditions on litter decomposition rates in forested tropical peatlands (but see Brady 1984;Yule and Gomez 2009). Furthermore, the trajectory from the chemistry of the initial litter to that of the organic material present in peat and the rate at which a more stable humified residue is formed remain poorly understood (Baumann et al 2009).…”