Abstract
Plant litter decomposition is an essential ecosystem function that contributes to carbon and nutrient cycling in streams. Aquatic shredders, mainly macroinvertebrates, can affect this process in various ways; they consume leaf litter, breaking it down into fragments and creating suitable habitats or resources for other organisms through the production of fine particulate organic matter (FPOM). However, measures of litter‐feeding traits across a wide range of aquatic macroinvertebrates are still rare. Here, we assessed the contributions of 11 species of freshwater macroinvertebrates to litter decomposition, by measuring consumption rate, FPOM production, and assimilation rate of highly decomposable (Alnus glutinosa) or poorly decomposable (Quercus robur) leaf litter types. In general, an increase in the quality of litter improved the litter consumption rate, and fungal conditioning of the leaf litter increased both the litter consumption rate and FPOM production. Macroinvertebrates specializing in leaf litter consumption also appeared to be the most sensitive to shifts in litter quality and the conditioning process. Contrary to expectations, the conditioning process did not increase the assimilation of low‐quality litter. There was a strong correlation between the relative consumption rate (RCR) of the two litter types, and the relative FPOM production (RFP) was strongly correlated to the RCR. These findings suggest a consistent relationship between RCR and macroinvertebrate identity that is not affected by litter quality, and that the RFP could be inferred from the RCR. The varying responses of the macroinvertebrate feeding traits to litter quality and the conditioning process suggest that the replacement of a shredder invertebrate species by another species could have major consequences for the decomposition process and the detritus‐based food web in streams. Further studies onto the importance of invertebrate identity and the effects of litter quality in a variety of freshwater ecosystems are needed to understand the whole ecosystem functioning and to predict its response to environmental changes.
Highlights
Leaf litter decomposition is an essential ecosystem function controlling the carbon and nutrient cycles in both terrestrial and aquatic ecosystems (Cadish & Giller, 1997; Gessner et al, 2010; Handa et al, 2014)
This study showed that leaf consumption and fine particulate organic matter (FPOM) production rates are mainly dependent on the macroinvertebrate species identity and the conditioning process, whereas the assimilation rate is strongly affected by the litter quality
Macroinvertebrates specializing in leaf litter consumption appeared to be the most sensitive to shifts in litter quality and the conditioning process
Summary
Leaf litter decomposition is an essential ecosystem function controlling the carbon and nutrient cycles in both terrestrial and aquatic ecosystems (Cadish & Giller, 1997; Gessner et al, 2010; Handa et al, 2014). This study tested (1) whether macroinvertebrate species differ in their litter-feeding traits; and how their feeding traits changes according (2) to the litter quality and (3) to the leaf fungal conditioning To answer these questions, a highly decomposable alder leaf litter (Alnus glutinosa, hereafter referred to as Alnus) and a poorly decomposable oak leaf litter (Quercus robur, hereafter referred to as Quercus) (Cornelissen, 1996; Foucreau, Puijalon, et al, 2013) were selected. It was predicted that the effects of the conditioning process would be higher in Quercus litter compared to Alnus litter, as Alnus litter is already a highly decomposable leaf litter
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