Leaf Nutrients and Macroinvertebrates Control Litter Mixing Effects on Decomposition in Temperate Streams

• Published in: Ecosystems (New York) Vol. 23; no. 2; pp. 400 - 416
• Main Authors: Santonja, Mathieu, Rodríguez-Pérez, Héctor, Le Bris, Nathalie, Piscart, Christophe
• Format: Journal Article
• Language: English
• Published: New York Springer Science + Business Media 01.03.2020; Springer US; Springer; Springer Nature B.V; Springer Verlag
• Subjects: Biodiversity and Ecology; Biological activity; Biomedical and Life Sciences; Calcium; Communities; Complementarity; Decomposition; Ecological function; Ecology; Environmental Management; Environmental Sciences; France; Geoecology/Natural Processes; Hydrology/Water Resources; Hypotheses; Invertebrates; Leaf litter; Leaves; Life Sciences; Macroinvertebrates; Magnesium; Microbial activity; Microorganisms; Niches; Nutrient concentrations; Nutrient content; Nutrients; Original Articles; plant litter; Plant Sciences; Plant species; Riparian vegetation; Streams; Temperate forests; trees; Zoology; France; litter nutrients; biodiversity–ecosystem functioning; litter traits; litter decomposition; temperate stream; community-weighted mean; functional trait dissimilarity; Biodiversity - ecosystem functioning; Functional trait dissimilarity; community weighted means
• ISSN: 1432-9840; 1435-0629
• DOI: 10.1007/s10021-019-00410-9

Plant litter decomposition is an essential ecosystem function in temperate streams. Both riparian vegetation and decomposer communities are major determinants of the decomposition efficiency and the interactions occurring within litter mixtures. However, the extent to which such litter mixture interactions are affected by combined shifts in litter traits and decomposer community is not well understood. We used leaf litter from 10 European tree species in order to study litter decomposition and litter mixture effects occurring in two-species litter mixtures in a temperate forested stream of northwestern France. The study distinguished between (1) decomposition involving microorganisms alone or together with invertebrates, and (2) decomposition involving litter mixtures of similar or dissimilar nutrient content. Increasing mean litter nutrient concentration favored both microbial activity and litter decomposition rate. Surprisingly, the highest litter mixture effects occurred in mixtures containing two nutrient-rich litters and occurred mainly in macroinvertebrate presence. Both the “mass ratio hypothesis,” expressed as the community-weighted mean traits (TraitCWM), and the “niche complementarity hypothesis,” expressed as the functional dissimilarity of litter traits (TraitFD), contributed to explain litter mixture effects. However, Trait CWM was found to be a better predictor than TraitFD. Finally, when evaluating the individual contributions of litter nutrients, calcium and magnesium appeared as important drivers of litter mixture effects. Our findings suggest that the mass ratio hypothesis overrules the niche complementarity hypothesis as a driver of litter diversity effects. Our study highlights the key importance of macroinvertebrates and of leaf nutrients, such as Ca and Mg, which are often neglected in decomposition studies in streams.