Leaf litter decomposition in tropical freshwater swamp forests is slower in swamp than non‐swamp conditions

Abstract

Decomposition is a key ecosystem function, and the rate of decomposition in forests affects their carbon storage potentials. Processes and factors determining leaf litter decomposition rates in dry-land and temperate forests are well understood, but these are generally poorly studied in tropical wetland forests, especially freshwater swamp forests (FSF). The home-field advantage (HFA) hypothesis predicts that soil microbes specialize in decomposing leaf litter produced by the tree species in their immediate vicinity. However, empirical support for the HFA is equivocal, and the HFA has never been tested in the highly heterogeneous and biodiverse ecosystems of tropical FSFs.We collected leaf litter from swamp and non-swamp tree species in a tropical FSF in Singapore and monitored the decomposition rates of these in swamp and non-swamp plots for a period of eight months. Leaf litter decomposed 3.7 times more slowly in swamp plots. Leaf litter from swamp tree species were significantly poorer in quality (higher C:N ratio) than those of non-swamp FSF tree species, but this had only a weak effect on decomposition rates. There was also only weak evidence for the HFA and only in non-swamp conditions. Our results show that while the leaf litter of tropical FSF swamp and non-swamp tree species differ significantly in chemical traits, litter decomposition rate is ultimately determined by local abiotic conditions, such as hydrology. Additionally, the high FSF tree diversity may prevent decomposer communities from specializing on any group of leaf litter types and thus limit the extent of HFA observed in such heterogeneous forests.

Leaf decomposition and flammability are largely decoupled across species in a tropical swamp forest despite sharing some predictive leaf functional traits

“…Leaf litter for decomposition experiments, flammability experiments and litter trait measurements was collected between July 2020 and January 2021 from 10 replicate 400 m 2 long-term vegetation plots (from a total of 40 plots) established in 2013 (described in Chong et al, 2021;Lam et al, 2021Lam et al, , 2022. Freshly fallen leaf litter was collected from 1 m long × 1 m wide litter traps suspended at least 1 m above the ground on a fortnightly basis (Lam et al, 2021).…”

“…Leaf litter for decomposition experiments, flammability experiments and litter trait measurements was collected between July 2020 and January 2021 from 10 replicate 400 m 2 long-term vegetation plots (from a total of 40 plots) established in 2013 (described in Chong et al, 2021;Lam et al, 2021Lam et al, , 2022. Freshly fallen leaf litter was collected from 1 m long × 1 m wide litter traps suspended at least 1 m above the ground on a fortnightly basis (Lam et al, 2021). Leaf litter was sorted within 24 h of collection and identified to species from which 21 canopy tree species were selected for the present study based on collection of sufficient leaf material for filling litterbags (to be described later; Table S1).…”

“…For tropical swamp forests, some studies have shown decomposability to be related to plant economic traits, for instance higher carbon : nitrogen ratios (CNR) slow decomposition (Lam et al ., 2021). Yet for tree species adapted to anoxic swamp environments, decomposability can also be impacted by physical traits; for example, species with thicker leaves can decompose faster (Yule & Gomez, 2009; Lam et al ., 2021). Tropical swamp forest traits have evolved in low decomposability–low flammability environments, but habitat degradation via clearing and draining transforms such environments into high decomposability–high flammability environments, and, thus, an important testing ground for potential trait‐driven decoupling between decomposability and flammability.…”

“…In contrast to flammability, decomposability generally varies along a plant economic spectrum governed by nutrient stoichiometry, morphology and physiology, for instance plant litter with low nutrient concentrations and thicker leaves generally have slower rates of decomposition (Santiago, 2007;Freschet et al, 2012Freschet et al, , 2013. For tropical swamp forests, some studies have shown decomposability to be related to plant economic traits, for instance higher carbon : nitrogen ratios (CNR) slow decomposition (Lam et al, 2021). Yet for tree species adapted to anoxic swamp environments, decomposability can also be impacted by physical traits; for example, species with thicker leaves can decompose faster (Yule & Gomez, 2009;Lam et al, 2021).…”

Waterlogging and soil but not seedling competition structure tree communities in a catchment containing a tropical freshwater swamp forest

“…However, non-peat freshwater swamp forests of the Asian tropics perform similar ecosystem functions such as carbon sequestration (Lam et al, 2021) and face similar pressures from land conversion or in-filling as other wetland vegetation (Corner, 1978;Chong et al, 2018), and yet are particularly understudied.…”