Decoupling shredder activity and physical abrasion in leaf litter decomposition process: experiments in the Torna-stream (Hungary) affected by red sludge spill

Differences in respiration rates and abrasion losses may muddle attribution of breakdown to macroinvertebrates versus microbes in litterbag experiments

“…Abrasion has also been evaluated by placing stones into coarse-mesh bags; one study found that stones increased leaf fragmentation by 45-93% over bags without stones (Heard et al, 1999). Another approach involved comparing leaf breakdown from coarse-mesh bags between times when macroinvertebrates had been extirpated due to a chemical spill, and a time when macroinvertebrates were present (Hubai et al, 2017). This study estimated that abrasion and drifting of fine particles from bags contributed between 5-47% of leaf mass loss (Hubai et al, 2017).…”

“…The role of abrasion in leaf litter breakdown depends on both environmental and leaf properties. Abrasive flows should have the biggest influence when sediment loads and water velocities are high (Hubai et al, 2017), and softer leaves may be more susceptible to mechanical abrasion (dos Santos Fonseca, Bianchini, Pimenta, Soares, & Mangiavacchi, 2013). Ferreira et al (2006) incubated leaves in artificial channels without macroinvertebrates or sediment and found no effect of velocity, with treatments as high as 2.35 m s −1 .…”

“…The paired litterbag technique also assumes that the difference in breakdown rate between coarse‐ and fine‐mesh bags is attributable primarily to macroinvertebrate consumption. This assumption ignores other mechanisms of mass loss that may be greater in coarse‐ than in fine‐mesh bags, such as physical abrasion (Ferreira, Graça, De Lima, & Gomes, 2006; Heard, Schultz, Ogden, & Griesel, 1999; Hubai et al, 2017). Abrasion effects on leaves may be greater in coarse‐mesh bags, as the wider mesh openings may lead leaves to experience higher water velocities (Moulton, Magalhães‐Fraga, Brito, & Barbosa, 2010) and greater physical fragmentation caused by suspended sediment relative to fine‐mesh bags (Spänhoff, Augspurger, & Küsel, 2007).…”

Traits or habitat? Disentangling predictors of leaf‐litter decomposition in Amazonian soils and streams

“…); (5) abrasion by water flow may increase stream litter breakdown rates (Hubai et al. ); and (6) the upstream‐to‐downstream transport of processed OM and nutrients, which may favor litter species decay in streams (e.g., Graça et al. ).…”

“…This process is generally constrained by the same extrinsic factors (e.g., temperature, water availability, nutrients) in streams and soils (Grac ßa 2001, Lecerf et al 2005, Kaspari et al 2008, Schindler and Gessner 2009, Grac ßa et al 2015, but these two types of habitats differ fundamentally in a number of ways, precluding generalization. The principal differences between these two types of habitat are (1) temperature range, which is buffered in streams; (2) water availability, which may be limited in terrestrial habitats; (3) oxygen levels, which may be limited in Amazonian headwater streams (especially when current is very low and/or litter is buried by sediment) but not in the superficial soil layer of terrestrial systems; (4) resource availability, which is more homogeneous in streams, as water flow favors nutrient dilution and food transportation, and more patchy in soils, with a distribution dependent on winds and rainfall, topography, the underlying parental rock, and nearby plants (e.g., John et al 2007); (5) abrasion by water flow may increase stream litter breakdown rates (Hubai et al 2017); and (6) the upstream-todownstream transport of processed OM and nutrients, which may favor litter species decay in streams (e.g., Grac ßa et al 2015).…”