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Alder (Alnus glutinosa) and oak (Quercus robur) are dominant tree species in European Atlantic mixed forests, and their leaf litter is a key resource for stream ecosystems. While alder litter has higher nutrient content and palatability than other species and is rapidly processed in the stream by detritivores and microorganisms, oak litter is a tougher and less nutritious but more persistent resource. Given that both species are declining due to the spread of the fungal pathogens Phytophthora alni and Phytophthora cinnamomi, respectively, we investigated how their reduction or loss might alter stream ecosystem functioning through changes in litter decomposition, invertebrate detritivore (Sericostoma pyrenaicum) growth and stoichiometry, and fungal decomposer assemblage characteristics.We conducted a microcosm experiment where we incubated litter mixtures representing different scenarios of alder and oak reduction or loss (and a concomitant increase in the other species), compared to a control that contained the four most common species in the study area (alder, oak, hazel [Corylus avellana] and willow [Salix atrocinerea]) in the same proportions as found in nature. The experiment lasted for 9 weeks, with the above variables measured every 3 weeks.Decomposition rates changed depending on which species was lost. Rates decreased as a result of alder loss and increased following oak loss. Sericostoma nutrient assimilation also responded to species loss, increasing and decreasing following alder and oak loss, respectively, possibly due to compensatory assimilation. Differences in Sericostoma nutrient concentrations among treatments decreased with time in the case of nitrogen, whereas they increased for phosphorus, probably due to microbial colonisation.The presence of oak also constrained microbial activity at the end of the experiment, reducing sporulation rates and causing differences in assemblage structure, probably due to inhibitory traits such as tannins or phenolic compounds.Treatments examining the loss of both species did not differ from the control, either in decomposition or sporulation rate, since loss of both alder and oak counteracted their effects. However, sporulation rates were higher for the scenario with loss of both species than for treatments with either alder reduction or loss, whereas sporulation rate and assemblage structure in the treatment with loss of both species were similar to the scenarios with oak reduction and loss, indicating that oak loss is more important for microbial activity.Changes in nutrient assimilation throughout the experiment suggested that effects of plant species reduction and loss can alter ecosystem functioning depending not only on litter palatability, but also on detritivore life stage. Overall, our results provide evidence for the importance of maintaining native riparian vegetation to preserve various ecosystem functions. [ABSTRACT FROM AUTHOR]

Leaf litter decomposition is a key process in stream ecosystems, the rates of which can vary with changes in litter quality or its colonization by microorganisms. Decomposition in streams is increasingly used to compare ecosystem functioning globally, often requiring the distribution of litter across countries. It is important to understand whether litter sterilization, which is required by some countries, can alter the rates of decomposition and associated processes. We examined whether litter sterilization with gamma irradiation (25 kGy) influenced decomposition rates, litter stoichiometry, and colonization by invertebrates after weeks of instream incubation within coarse-mesh and fine-mesh litterbags. We used nine plant species from three families that varied widely in litter chemistry but found mostly consistent responses, with no differences in decomposition rates or numbers of invertebrates found at the end of the incubation period. However, litter stoichiometry differed between irradiated and control litter, with greater nutrient losses (mostly phosphorus) in the former. Therefore, the effects of irradiation on litter chemistry should be taken into account in studies focused on stoichiometry but not necessarily in those focused on decomposition rates, at least within the experimental timescale considered here. [ABSTRACT FROM AUTHOR]

Leaf litter of alder (Alnus glutinosa) is a key resource to detrital stream food webs. Due to its high quality and palatability, it is readily colonised by microorganisms and consumed by detritivores, contributing significantly to carbon and nutrient cycling and to ecosystem functioning. Given that this species has declined due to the spread of the pathogen Phytophthora alni, we investigated how its loss would alter leaf litter decomposition and associated stream assemblages of aquatic hyphomycetes and invertebrates, in a field experiment conducted in three streams. We compared litter mixtures containing alder plus three other species (Corylus avellana, Quercus robur and Salix atrocinerea; that is, 4-species treatments) with mixtures that excluded alder (3-species treatments) and all the monocultures (1-species treatments). The loss of alder reduced decomposition rates, despite the existence of an overall negative diversity effect after 3 weeks of exposure (that is, monocultures decomposed faster than mixtures) and no diversity effect after 6 weeks. Aquatic hyphomycete and detritivore assemblage structure in the mixture without alder differed from those of the mixture with alder and the monocultures, and the former had lower fungal sporulation rate and taxon richness. Our results suggest that alder loss from the riparian vegetation can significantly slow down the processing of organic matter in streams and produce shifts in stream assemblages, with potential consequences on overall ecosystem functioning. We highlight the importance of assessing the ecological consequences of losing single species, particularly those especially vulnerable to stressors, to complement the multiple studies that have assessed the effects of random species loss. [ABSTRACT FROM AUTHOR]

Biodiversity loss is occurring globally at unprecedented rates, altering the functioning of the Earth's ecosystems. Multiple processes are often key components of ecosystem functioning, but it is unclear how biodiversity loss affects ecosystem multifunctionality (i.e., the ability of ecosystems to maintain multiple processes simultaneously). This is particularly true for some ecosystem types such as streams, which have been understudied, despite their key role in global biogeochemical cycles and their serious impairment by the widespread loss of riparian vegetation as a result of global change. Using a microcosm experiment, we tested whether losing riparian plant diversity affected stream multifunctionality, taking into account nine key processes related to litter decomposition, animal biomass production, and nutrient cycling, and simulating plant species loss from four to one in the presence or absence of litter‐feeding detritivores. Multifunctionality increased with plant diversity in the presence of detritivores and decreased in their absence, evidencing a key role of detritivores in biodiversity–ecosystem‐functioning (BEF) relationships. Moreover, by exploring effects of plant diversity on each process individually we were able to reveal potential mechanisms underlying BEF relationships; for example, effects of plant diversity on nutrient cycling occurred at least partly via indirect nutrient transfer, and were possibly accompanied by changes in microbial stoichiometry. Such mechanisms were unnoticeable when examining multifunctionality metrics, suggesting that individual processes provide crucial information to understand how stream ecosystem functioning is impaired by biodiversity loss. [ABSTRACT FROM AUTHOR]

The article offers information on how latitude dictates plant diversity effects on instream decomposition. It mentions that running waters contribute substantially to global carbon fluxes through decomposition of terrestrial plant litter by aquatic microorganisms and detritivores. It discusses the consequences of the latitudinal pattern indicates that loss of plant functional diversity.