Nutrient addition does not enhance leaf decomposition in a Southeastern Brazilian stream (Espinhaço mountain range)

Abstract

A decomposition experiment using eucalyptus leaves was carried out in a Southeastern Brazilian mountain stream located at the transition between the Cerrado and the Atlantic Forest to test whether nutrient addition increases microbial and invertebrate colonisation and accelerates breakdown rates. The results show that none of the tested variables was significantly affected by nutrient addition, despite the average increase in ATP concentrations and invertebrate colonisation observed in the fertilised leaf bags. This could mean that breakdown in the stream was already at its maximum due to the relatively high water temperature and nutrient content, or that the breakdown rate of eucalyptus leaves was too fast to allow the detection of any effects of nutrient addition. Breakdown rates of eucalyptus leaves were much faster than the values reported in literature for most species in Brazilian Cerrado streams, suggesting that the replacement of the natural vegetation by eucalyptus may affect nutrient dynamics in the region.Keywords: eucalyptus leaf breakdown, nutrients, ATP concentrations, macroinvertebrates, tropical stream. A adição de nutrientes não acelera a decomposição de folhas em um riacho do Sudeste do Brasil ResumoUm experimento de decomposição de folhas de eucalipto foi efetuado em um riacho do sudeste do Brasil, localizado na transição entre o Cerrado e a Mata Atlântica para testar se a adição de nutrientes aumenta a colonização das folhas por microrganismos e por invertebrados e se acelera a sua taxa de decomposição. Nenhuma das variáveis testadas foi significativamente afetada pela adição de nutrientes, apesar do aumento médio verificado nas concentrações de ATP e na colonização por invertebrados dos sacos contento detritos fertilizados. Isto pode significar que a decomposição no riacho já ocorria à taxa máxima devido à temperatura e concentração de nutrientes relativamente elevadas da água ou que a taxa de decomposição das folhas de eucalipto foi demasiado rápida para permitir detectar qualquer efeito da adição de nutrientes. Os coeficientes de decomposição das folhas de eucalipto (0,1127 -0,1192 dia -1 ) foram mais elevados que os verificados na literatura para a maioria das espécies em riachos do Cerrado, sugerindo que o reflorestamento com eucalipto pode alterar a dinâmica dos nutrientes na região.Palavras-chave: decomposição de folhas de eucalipto, nutrientes, concentração de ATP, macroinvertebrados, riacho tropical.

Leaf traits induce the feeding preference of a shredder of the genusTriplectidesKolenati, 1859 (Trichoptera) in an Atlantic Forest stream, Brazil: a test with native and exotic leaves

“…However, when enriched and non-enriched discs of the same species were offered together, the larvae showed no preference, indicating that nutrient enrichment had a secondary effect on the behaviour of Triplectides sp. Abelho et al (2010) did not observe differences in the breakdown rates of enriched leaves of E. camaldulensis in a tropical stream and suggested that the rapid decomposition of this species was due to the relatively high temperature and nutrient concentrations in the water.…”

“…Given the importance of riparian vegetation to the detritus pool in low-order stream ecosystems (Gregory, Swanson, McKee, and Cummins 1991), human-induced alterations in riparian zones are likely to indirectly affect both the structure and function of aquatic decomposers (Dangles, Jonsson, and Malmqvist 2002). The invasion of riparian communities by exotic species changes leaf-litter availability and diversity in streams, influencing the activity of detritivores and the stream metabolism at the same time (Abelho, Moretti, França, and Callisto 2010). Schulze and Walker (1997), evaluating the effects of the exotic weeping willow Salix babylonica Linnaeus, 1753 in Australia, observed that these leaves decomposed faster than the native Eucalyptus camaldulensis Dehnhardt, 1832 and found different invertebrate assemblages on leaf packs of these species.…”

A meta‐analysis of the effects of nutrient enrichment on litter decomposition in streams

“…Nutrient enrichment at the litter bag scale, on the other hand, was often attempted by using diffusing substrates (e.g. fertilizer pellets or agarized media), which do not provide uniform controllable nutrient release at either temporal or spatial scales (Abelho & Graça, ; McKie et al , ; Abelho et al , ). Therefore, we suggest that this approach to address the effect of nutrient enrichment on litter decomposition should be abandoned.…”

Contrasting effects of functionally distinct tadpole species on nutrient cycling and litter breakdown in a tropical rainforest stream

“…Several studies have indicated that the effects of dissolved nutrients on litter breakdown and microbes colonising the litter strongly depend on the water background (e.g., concentrations in nitrogen and phosphorus). In some streams with relatively high background nutrient concentrations, neither litter breakdown rates (Royer & Minshall, ) nor fungal biomass were affected by nutrient enrichment (Abelho & Graça, ; Abelho, Moretti, França, & Callisto, ). In contrast, breakdown rate, microbial respiration, fungal and bacterial biomass, and the sporulation rate of aquatic hyphomycetes associated with decomposing leaf material were significantly higher in nutrient‐enriched streams than in relatively oligotrophic streams (Gulis & Suberkropp, ; Suberkropp & Chauvet, ).…”