Two microcrustaceans affect microbial and macroinvertebrate‐driven litter breakdown

Abstract

Summary Leaf litter degradation in fresh waters is a fundamental ecosystem process performed by a wide array of decomposers. The meiofauna is an important component of aquatic heterotrophic assemblages, which can provide a trophic link between plant detritus and associated microbial and macroinvertebrate communities, but their contribution to leaf breakdown remains poorly understood. We hypothesised that, through their feeding activity, microcrustaceans influence the structure of fungal assemblages and consequently microbially mediated litter breakdown. Litter‐associated microcrustaceans were predicted to change the pathways of energy transfer in the food web according to the positive (e.g. complementarity) or negative (e.g. predation) interactions with macroinvertebrate detritivore taxa. We evaluated experimentally in the laboratory, over 6 and 13 days, the potential contribution of two freshwater microcrustaceans (a cladoceran and a copepod) to litter breakdown in the presence of microfungi (aquatic hyphomycetes), with and without macroinvertebrate detritivores (a trichopteran and a gammarid amphipod). The presence of microcrustaceans enhanced leaf mass loss by 62 and 22% in treatments with fungi or trichopteran alone, respectively, while no significant effect was observed for treatments with the amphipod. Microcrustaceans strongly increased the production of fine particulate organic matter, particularly in treatments with fungi alone (+637%). The leaf consumption rate by the amphipod significantly decreased (−61%) at 13 days in the presence of microcrustaceans, likely due to predation on cladocerans. Our study supports the potential role of microcrustaceans in the detrital food web of streams and rivers. Interestingly, microcrustaceans may interact with microbial and macroinvertebrate decomposers in either positive or negative ways. Therefore, microcrustaceans add complexity to detrital food webs by increasing vertical diversity and modulating biotic interactions with important consequences for carbon and energy transfers in stream ecosystems.

Meiofauna promotes litter decomposition in stream ecosystems depending on leaf species

“…For instance, fungivorous nematodes (e.g., from the Aphelenchida) have very specific fungal diets (Dighton, Zapata, & Ruess, 2000). The selective feeding of meiofauna could reduce the growth of some fungi taxa, while promoting others, thereby reducing the competition for resources between different fungi species (Chambord et al, 2017). Indeed, the meiofauna reduced the relative abundance of Alatospora acuminata and T. Marchalianum but increased T. elegans and Penicillium italicum that showed specific ligninolytic activities (Hofmann et al, 2016;Osono, 2007).…”

“…litter decomposition process, macrofauna, meiofauna, microbes, trophic complexity While the contributions of fungi and shredding macroinvertebrates in litter decomposition have been well documented, the role of the meiofauna is rarely reported in the decomposition process (Palmer, 1997;Swan & Palmer, 2000). Indeed, growing evidence suggests the potential importance of meiofauna in litter decomposition (Ágoston-Szabó, Schöll, Kiss, & Dinka, 2016;Chambord, Tackx, Chauvet, Escolar, & Colas, 2017;Perlmutter & Meyer, 1991).…”

“…Some meiofauna, such as rotifers and nematodes, feed on the associated biofilms. The grazing may alter the microbial abundance and/or the community structure, increasing or decreasing the microbial decomposition activity of microbes (Chambord et al, 2017).…”

“…While the contributions of fungi and shredding macroinvertebrates in litter decomposition have been well documented, the role of the meiofauna is rarely reported in the decomposition process (Palmer, 1997; Swan & Palmer, 2000). Indeed, growing evidence suggests the potential importance of meiofauna in litter decomposition (Ágoston‐Szabó, Schöll, Kiss, & Dinka, 2016; Chambord, Tackx, Chauvet, Escolar, & Colas, 2017; Perlmutter & Meyer, 1991). Meiofauna, regarded as an important component of the benthic community, include diverse species that are associated with leaf detritus (Hakenkamp & Morin, 2000).…”

“…Some meiofauna, such as rotifers and nematodes, feed on the associated biofilms. The grazing may alter the microbial abundance and/or the community structure, increasing or decreasing the microbial decomposition activity of microbes (Chambord et al., 2017). Also, the bioturbation effect of meiofauna can indirectly affect the process of microbial decomposition by changing the microenvironment associated with decomposition (oxygen, organic concentration, etc.)…”