| Summary: | Plant litter represents a major basal resource in streams, where its decomposition is partly regulated by litter traits. Litter-trait variation may determine the latitudinal gradient in decomposition in streams, which is mainly microbial in the tropics and detritivore-mediated at high latitudes. However, this hypothesis remains untested, as we lack information on large-scale trait variation for riparian litter. Variation cannot easily be inferred from existing leaf-trait databases, since nutrient resorption can cause traits of litter and green leaves to diverge. Here we present the first global-scale assessment of riparian litter quality by determining latitudinal variation (spanning 107°) in litter traits (nutrient concentrations; physical and chemical defences) of 151 species from 24 regions and their relationships with environmental factors and phylogeny. We hypothesized that litter quality would increase with latitude (despite variation within regions) and traits would be correlated to produce ?syndromes? resulting from phylogeny and environmental variation. We found lower litter quality and higher nitrogen:phosphorus ratios in the tropics. Traits were linked but showed no phylogenetic signal, suggesting that syndromes were environmentally determined. Poorer litter quality and greater phosphorus limitation towards the equator may restrict detritivore-mediated decomposition,contributing to the predominance of microbial decomposers in tropical streams. Fil: Boyero, Luz. Basque Foundation for Science; España. James Cook University; Australia. Universidad del País Vasco; España Fil: Graça, Manuel A. S. Universidad de Coimbra; Portugal Fil: Tonin, Alan M. Universidade do Brasilia; Brasil Fil: Pérez, Javier. Universidad del País Vasco; España Fil: Swafford, Andrew J. University of California; Estados Unidos Fil: Ferreira, Verónica. Universidad de Coimbra; Portugal Fil: Landeira Dabarca, Andrea. Universidad de Coimbra; Portugal. Universidad de Vigo; España Fil: Alexandrou, Markos A. Wildlands Conservation Science; Estados Unidos Fil: Gessner, Mark O. Department of Experimental Limnology, Leibniz Institute of Freshwater Ecology and Inland Fisheries; Alemania. Berlin Institute of Technology; Alemania Fil: McKie, Brendan G. Swedish University of Agricultural Sciences; Suiza Fil: Albariño, Ricardo Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; Argentina Fil: Barmuta, Leon A. University of Tasmania; Australia Fil: Callisto, Marcos. Universidade Federal do Minas Gerais; Brasil Fil: Chará, Julián. Centro para la Investigación en Sistemas Sostenibles de Producción Agropecuaria (CIPAV); Colombia Fil: Chauvet, Eric. Université de Toulouse; Francia Fil: Colón Gaud, Checo. Georgia Southern University; Estados Unidos Fil: Dudgeon, David. The University of Hong Kong; China Fil: Encalada, Andrea C. Universidad de Coimbra; Portugal. Universidad San Francisco de Quito; Ecuador Fil: Figueroa, Ricardo. Universidad de Concepción; Chile Fil: Flecker, Alexander S. Cornell University; Estados Unidos Fil: Fleituch, Tadeusz. Polish Academy of Sciences; Polonia Fil: Frainer, André. UiT The Arctic University of Norway; Noruega Fil: Gonçalves Jr., José F. Universidade do Brasilia; Brasil Fil: Helson, Julie E. University of Toronto; Canadá Fil: Iwata, Tomoya. University of Yamanashi; Japón Fil: Mathooko, Jude. Egerton University; Kenia Fil: M' Erimba, Charles. Egerton University; Kenia Fil: Pringle, Catherine M. University of Georgia; Estados Unidos Fil: Ramírez, Alonso. Universidad de Puerto Rico; Puerto Rico Fil: Swan, Christopher M. University of Maryland; Estados Unidos Fil: Yule, Catherine M. Monash University; Australia Fil: Pearson, Richard G. James Cook University; Australia
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