Effects of litter size and quality on processing by decomposers in a tropical savannah stream

Abstract

Litter fragment size and quality can have profound effects on ecosystem functioning and global biogeochemical cycling due to differential utilization by decomposers. Here we study the influence of these factors on decomposers from two guilds found in a tropical savannah stream: invertebrate shredders of the genus Phylloicus and microorganisms. Containers (16 × 16 × 12 cm, ~ 3L) with either Phylloicus (cases removed; N = 16) or stream water containing microorganisms (N = 16) were supplied with litter from the species Inga laurina, Maprounea guianensis, and Richeria grandis, and cut into disks of 18.7, 13.2, and 8.1 mm in diameter (3 sizes × 3 species = 9 disks per container). Relative decomposition was greater for smaller leaf disks and disks of higher quality in microbial‐only cultures. Phylloicus preferentially harvested large fragments for case building, also preferring the leaves of M. guianensis and R. grandis, likely due increased robustness for case formation. Microbial decomposition resulted in ~20% litter mass loss compared to 30% in Phylloicus (of which 8% was used for case building and 24% for food). Thus, changes to input litter size, such as a decrease in leaf size after drought, may alter microbial decomposition and potentially affect shredder populations by limiting the availability of casing material.

Effects of Drying and Re-Wetting on Litter Decomposition and Nutrient Recycling: A Manipulative Experiment

“…Results of the statistical analyses suggest that these three factors are sometimes interplaying, as indicated by significant interaction terms (e.g., macrofauna:leaf size for oxygen demand and N content in residual biomass or macrofauna:drying on P percentage in residual biomass). Our results confirm findings from different studies addressing single factors as regulators of decomposition rates [10,17,40]. In particular, highest rates of biomass loss during the nearly 40 days of incubation of the litter material were recorded in microcosms permanently submerged containing leaves with larger diameter and macrofauna.…”

“…Our results may be realistic for the litter material we employed and for the macrofauna species we selected but not always. In fact, other studies report higher soluble compounds release and faster degradation in small litter fragments characterized by high surface-area-to-volume ratio, due to higher microbial colonization [17,53]. Overall, results from this study are relevant as under climate change scenario drying events will be more frequent and more prolonged [1,45] and the understanding of their consequences for low order stream metabolism is central.…”

“…Organic matter breakdown may also be influenced by leaf size [17,18]. Leaf size and geometry (e.g., flat, large surfaces) may facilitate the conditioning action that macrofauna produces on leaves and result in higher colonization by a biofilm of bacteria, fungi and algae [17,19]. During skeletonization of large leaves, the lignin to cellulose ratio may increase significantly and influence the residual organic matter breakdown [19].…”

Food preference of Phylloicus sp. (Insecta: Trichoptera): experimental study with plant species from the Cerrado

“…In the Gallery Forest vegetation of the Cerrado, some species have low-quality leaves with high concentrations of lignin, cellulose, tannins, and polyphenols (De Sousa-Neto, Lins & Martins 2017, Rezende, Leite, & Ramos 2018), making consumption by shredders challenging (Rezende et al 2021). To date, only seven articles have conducted experimental studies using shredder aquatic insects from Cerrado streams in laboratories (Ferreira et al 2015, Rezende, Leite, & Ramos 2018, Reis et al 2018, Moretti & Santos 2019, Sena et al 2020, Rezende 2021. It is known that the genera Phylloicus (Mueller 1880), Tipula (Linnaeus 1758), Simulium (Latreille 1802), and Chironomus (Meigen 1803) can be used for such purposes.…”