Leaf Litter Decomposition of Three Riparian Tree Species and Associated Macroinvertebrates of Eswathu Oya, a Low Order Tropical Stream in Sri Lanka

Abstract

Leaf decomposition, an important component of the organic matter dynamics in streams, has been widely examined in temperate regions but much less documented in tropical regions. We report here the first study of leaf decomposition in a Sri Lankan stream. The litterbag technique was used. Coarse (8 mm) and fine (100 μm) litterbags, that included or excluded macroinvertebrates respectively, were used to enclose leaves of three dominant riparian tree species: native Ochlandra stridula (bamboo), and the introduced Alstonia macrophylla and Hevea brasiliensis (rubber). A fourth set of litterbags contained a mixture of these three species. Leaf colonization by macroinvertebrates was highest in the early stages of the decomposition process on Hevea leaves but invertebrate densities declined later. The opposite colonization effect was observed on the native Ochlandra leaves: slow colonization with continuing low densities from the beginning to the end of the process. Decomposition of all three species was significantly faster in the coarse than in the fine mesh bags. Alstonia, which has the softest leaf tissue, was most rapidly decomposed while Ochlandra, with its tough structure, was the slowest. Among the invertebrates, insects were the most important leaf colonizing animals, with Diptera, Coleoptera and Trichoptera the most dominant. The invertebrate variety in the mixed bags was higher than in the singlespecies leaf bags, where Chironomidae dominated the colonizing assemblages. This study has shown that toughness, indicated by the 'specific weight of leaf tissue', and the quality of the leaves was more important in determining breakdown rates than their origin.

Colonization by oligochaetes (Annelida: Clitellata) in decomposing leaves ofEichhornia azurea(SW.) Kunth (Pontederiaceae) in a neotropical lentic system

“…Higher values of these variables accelerate the decomposition process, through the increase of the decomposer organisms' metabolism (Gulis and Suberkropp, 2003;Swan and Palmer, 2004). Besides this, the experimental design can influence the results, such as the use of senescent versus green leaves, the quantity of leaves used and the mesh size of the litter bags (Boulton and Boon, 1991;Walpola et al, 2011).…”

A conceptual model of litter breakdown in low order streams

“…The role of shredders is, however, variable in tropical climatic zones. Shredders have been reported as locally abundant and/or important for litter breakdown in Puerto Rico (Crowl et al, ; Cross et al, ), the Australian wet tropics (Cheshire et al, ; Camacho et al, ), Hong Kong (Li and Li, ), Malaysia (Yule et al, ), montane Ecuador (Encalada et al, ), Costa Rica (Benstead, ), Sri Lanka (Walpola et al, ) and the Colombian Andes (Chará‐Serna et al, ). However, they seem to be absent or scarce in other regions, mostly in tropical rain forests and savannas in Costa Rica (Irons et al, ; Rosemond et al, ), Colombia (Mathuriau and Chauvet, ; Rueda‐Delgado et al, ), the Brazilian Cerrado (Wantzen and Wagner, ; Gonçalves et al, ), Hong Kong (Li et al, ; Dudgeon and Gao, ), Papua New Guinea (Yule, ) and Hawaii (Larned et al, ), and in some Mediterranean streams of the Iberian Peninsula (Gonçalves et al, ; Pérez et al, ).…”

Leaf litter traits predominantly control litter decomposition in streams worldwide

“…Second, high microbial activities at low latitudes are counteracted by low invertebrate activities (Haapala, Muotka, & Markkola, ; Walpola, Leichtfried, Amarasinghe, & Füreder, ). Irons et al () explored litter decomposition processes in streams across a latitudinal gradient and concluded that the contribution of the invertebrates to litter decomposition increases with latitude, whereas the proportion attributable to microbes concomitantly decreases with increasing latitude (Haapala et al, ; Leite‐Rossi et al, ; Mathuriau & Chauvet, ; Tonin, Hepp, Restello, & Gonçalves, ; Walpola et al, ). Consistent with our results, for example, Boyero et al () reported unchanged decomposition rates driven by both microbes and invertebrates in an experiment across 22 sites along a latitudinal gradient (0.37–47.8°).…”