Riparian plant litter is a major energy source for forested streams across the world and its decomposition has repercussions on nutrient cycling, food webs and ecosystem functioning. However, we know little about plant litter dynamics in tropical streams, even though the tropics occupy 40% of the Earth’s land surface. Here we investigated spatial and temporal (along a year cycle) patterns of litter inputs and storage in multiple streams of three tropical biomes in Brazil (Atlantic forest, Amazon forest and Cerrado savanna), predicting major differences among biomes in relation to temperature and precipitation regimes. Precipitation explained most of litter inputs and storage, which were generally higher in more humid biomes (litterfall: 384, 422 and 308 g m−2 y−1, storage: 55, 113 and 38 g m−2, on average in Atlantic forest, Amazon and Cerrado, respectively). Temporal dynamics varied across biomes in relation to precipitation and temperature, with uniform litter inputs but seasonal storage in Atlantic forest streams, seasonal inputs in Amazon and Cerrado streams, and aseasonal storage in Amazon streams. Our findings suggest that litter dynamics vary greatly within the tropics, but point to the major role of precipitation, which contrasts with the main influence of temperature in temperate areas.

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Aim We evaluated the effect of the presence of Hovenia dulcis Thunb. (Rhamnaceae) in riparian zones on the organic matter dynamics of small subtropical streams. Methods We conducted this study in three subtropical Atlantic Forest streams with different densities of H. dulcis in riparian vegetation located in southern Brazil. In each stream, we quantified the input of allochthonous organic matter for one year using buckets (area: 0.04 m2/bucket) suspended about 1 m from the streambed in three different sections (15 buckets/stretch = 45 buckets/stream). Monthly, the plant material retained in the buckets was collected individually, dried (40±5 °C/72 h), identified (native litter together and H. dulcis litter alone) and weighed. Results The largest input of native organic matter occurred during the winter months (~55 g.m-2), ranging from ~31 g.m-2 (summer) to ~46 g.m-2 (spring) over the year. The input of H. dulcis organic matter was concentrated in the autumn (~56 g.m-2) and summer (~28 g.m-2), being scarce in the other seasons (~3 g.m-2 in the spring and winter). Only the contribution of native organic matter was associated with precipitation. Contrary to that observed with native vegetation (input of organic matter related with rainfall), H. dulcis input was related to the phenology of the species, which is deciduous, with leaf fall strongly marked, occurring especially during the autumn. Conclusions When present at high densities (dominant), the presence of H. dulcis in riparian stream vegetation makes the supply of allochthonous plant resources scarce at some periods of the year, altering the energy availability in these ecosystems and, potentially, the functioning of subtropical streams.

Context In headwater streams, allochthonous litterfall input is an essential process to maintain the ecosystem functioning. The presence of non-native species in the riparian vegetation, with phenological characteristics distinct from those of most native tree species, can alter this process. Aims We evaluated the effect of the phenology of a non-native species (Hovenia dulcis) on the temporal patterns and biomass of litterfall input into streams by comparing one stream with (Hovenia stream) and another without (Native stream) H. dulcis in their riparian vegetation. Methods We quantified the litterfall input from native tree species and H. dulcis for 1 year by using buckets suspended above the streambeds. Key results The temporal pattern of litterfall input changed between streams, with quantitative differences between them during autumn and winter. In the Native stream, litterfall input was slightly higher in spring (∼79 g m−2 month−1), followed by winter (∼68 g m−2 month−1) and autumn (∼54 g m−2 month−1), whereas in the Hovenia stream, it was concentrated in autumn (∼126 g m−2 month−1). Conclusions and implications Our results indicated that the presence of H. dulcis in the riparian vegetation, when in high density, changes the temporal pattern and biomass of litterfall input into subtropical streams.

Neste estudo, avaliamos o efeito da presença de agricultura na zona ripária de riachos sobre o processo de decomposição foliar e a estrutura e composição da comunidade de invertebrados aquáticos. Este estudo foi realizado em três riachos subtropicais de Mata Atlântica com diferentes níveis de perturbação agrícola (baixa, média e alta). Em cada riacho foram incubados litter bags de malha fina e grossa contendo folhas de Nectandra megapotamica (Spreng.) Mez. Após 7, 15 e 30 dias, um conjunto de litter bags foi retirado para a quantificação das taxas de decomposição e remoção dos invertebrados associados. As taxas de decomposição foram semelhantes para a malha fina. Para a malha grossa, entretanto, as taxas de decomposição foram maiores no riacho de baixa agricultura. A riqueza de invertebrados foi semelhante entre os riachos, enquanto a abundância de invertebrados foi maior nos riachos de baixa e alta agricultura. A composição taxonômica e a abundância de alguns grupos tróficos funcionais diferiram entre os riachos. Embora estudos sejam necessários para verificar a manutenção desses padrões, os resultados deste estudo indicaram que a presença de agricultura na zona ripária dos riachos pode afetar o processo de decomposição foliar e as comunidades de invertebrados aquáticos

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