Future increase in temperature may stimulate litter decomposition in temperate mountain streams: evidence from a stream manipulation experiment

Abstract

Summary Small woodland streams constitute the majority of water courses in many catchments. Given their generally low water temperature, high surface : volume ratio and primarily heterotrophic nature, such streams can be strongly affected by increases in temperature. It is therefore important to assess how stream communities and processes respond to the global warming projected for this century. We assessed the effects of a c. 3 °C experimental warming of stream water on decomposition of Quercus robur leaf litter and on the associated fungal biomass (ergosterol concentration), sporulation rates of aquatic hyphomycetes, and total macroinvertebrate and shredder abundance in spring, autumn and winter. A mountain stream reach in central Portugal was divided longitudinally over 22 m with local stones. The study followed a before‐after control‐impact design, with both stream halves at ambient temperature during 1 year and one stream half being experimentally warmed in the second year. Experimental warming of stream water stimulated litter decomposition only in winter, probably because at that time, the low natural temperature limited microbial activities. The effect of experimental warming did not depend on the presence of macroinvertebrates. Contrary to expectations, no significant effect of experimental warming was found on fungal biomass accrual, sporulation rate of aquatic hyphomycetes or macroinvertebrate abundance on decomposing litter. Although the stimulation of litter decomposition in winter could lead to food depletion, this is unlikely when streams are subsidised by more recalcitrant leaves such as oak, which enter the stream in later winter and decompose slowly.

Gammarus pulex (Crustacea: Amphipoda) avoids increasing water temperature and intraspecific competition through vertical migration into the hyporheic zone: a mesocosm experiment

“…This result expands on recent studies suggesting that leaf litter decomposition will increase with rising water temperatures due to enhanced microbial decomposition and invertebrate activity rates (e.g., Ferreira and Canhoto 2015;Mas-Martí et al 2015). Our results suggest decomposition rates will be reduced when temperatures and/or competition increase beyond thresholds that cause a behavioral response of shredding invertebrates to enter the hyporheic zone.…”

Leaf litter traits predominantly control litter decomposition in streams worldwide

“…First, the positive impacts of high stream water temperature are counteracted by low water dissolved O 2 at low latitudes (Iñiguez‐Armijos et al, ; Lopes, Martins, Silveira, & Alves, ). High temperature usually stimulates litter decomposition (Ferreira & Canhoto, ; Ferreira, Chauvet, et al, ). However, water dissolved O 2 in streams usually decreases significantly with increasing water temperatures (Gonçalves et al, ; Iñiguez‐Armijos et al, ; Pettit et al, ).…”

“…Generally, the decomposition of leaf litter in streams is mainly driven by both extrinsic (e.g., environmental factors and water characteristics of streams; Rosemond et al, ; Woodward et al, ) and intrinsic factors (e.g., litter traits; Gonçalves et al, ; Jinggut & Yule, ; Lecerf & Chauvet, ; Leite‐Rossi et al, ). Of the dozens of extrinsic factors that can influence litter decomposition in streams, such as temperature, dissolved nutrients, pH and dissolved oxygen (O 2 ), temperature has undoubtedly captured more than its fair share of attention (Ferreira & Canhoto, ; Ferreira, Chauvet, & Canhoto, ; Follstad Shah et al, ). For example, many studies have found a positive temperature–decomposition relationship, with faster decomposition in tropical compared with temperate streams, mainly attributable to higher water temperatures favouring increased biological activity (e.g., Ardón, Pringle, & Eggert, ; Ferreira & Canhoto, ; Ferreira & Chauvet, ).…”

“…Of the dozens of extrinsic factors that can influence litter decomposition in streams, such as temperature, dissolved nutrients, pH and dissolved oxygen (O 2 ), temperature has undoubtedly captured more than its fair share of attention (Ferreira & Canhoto, ; Ferreira, Chauvet, & Canhoto, ; Follstad Shah et al, ). For example, many studies have found a positive temperature–decomposition relationship, with faster decomposition in tropical compared with temperate streams, mainly attributable to higher water temperatures favouring increased biological activity (e.g., Ardón, Pringle, & Eggert, ; Ferreira & Canhoto, ; Ferreira & Chauvet, ). Conversely, other studies have found higher litter decomposition rates in temperate compared with tropical streams (Ferreira, Encalada, & Graça, ; Gonçalves, Graça, & Callisto, , ), largely attributable to favourable conditions, such as cool, well‐aerated, flowing water preferred by aquatic hyphomycetes.…”

A decomposição de detritos foliares de espécies nativas e exótica e a colonização de macroinvertebrados em um riacho tropical localizado na Floresta Nacional de Ipanema, SP, Brasil

“…Outro fator importante da decomposição foliar é a temperatura que influencia no desenvolvimento de organismos gerando condições ótimas para estes. Em menores temperaturas, a colonização pode ser mais lenta ou a ação de bactérias e fungos mais baixa, sendo seu metabolismo mais lento, e isto pode modificar o processo de decomposição não acondiçoando os detritos dispostos (Ferreira & Canhoto, 2015;Mas-Martí et al, 2015; A densidade da fauna nas diferentes datas do experimento, tiveram diferenças por fatores já mencionados (físicos, químicos, biológicos e climáticos), e estes relacionados com as perturbações físicas, presença de predadores e disponibilidade de alimento entre outras, estas variações além de ser em escala temporal, também apresentou diferenças nas densidades nos três tratamentos testados. Alguns grupos (Odonata, Diptera, Coleoptera, Ephemeroptera e Trichoptera), são organismos muito importantes, sendo diversos e sensíveis (Maloney et al 2009;Wagenhoff et al, 2012).…”