Long‐term effects of fungicides on leaf‐associated microorganisms and shredder populations—an artificial stream study

Abstract

Leaf litter is a major source of carbon and energy for stream food webs, while both leaf-decomposing microorganisms and macroinvertebrate leaf shredders can be affected by fungicides. Despite the potential for season-long fungicide exposure for these organisms, however, such chronic exposures have not yet been considered. Using an artificial stream facility, effects of a chronic (lasting up to 8 wk) exposure to a mixture of 5 fungicides (sum concentration 20 μg/L) on leaf-associated microorganisms and the key leaf shredder Gammarus fossarum were therefore assessed. While bacterial density and microorganism-mediated leaf decomposition remained unaltered, fungicide exposure reduced fungal biomass (≤71%) on leaves from day 28 onward. Gammarids responded to the combined stress from consumption of fungicide-affected leaves and waterborne exposure with a reduced abundance (≤18%), which triggered reductions in final population biomass (18%) and in the number of precopula pairs (≤22%) but could not fully explain the decreased leaf consumption (19%), lipid content (≤43%; going along with an altered composition of fatty acids), and juvenile production (35%). In contrast, fine particulate organic matter production and stream respiration were unaffected. Our results imply that long-term exposure of leaf-associated fungi and shredders toward fungicides may result in detrimental implications in stream food webs and impairments of detrital material fluxes. These findings render it important to understand decomposer communities' long-term adaptational capabilities to ensure that functional integrity is safeguarded. Environ Toxicol Chem 2017;36:2178-2189. © 2017 SETAC.

A common fungicide impairs stream ecosystem functioning through effects on aquatic hyphomycetes and detritivorous caddisflies

“…Our experiment showed that the fungicide impaired the survival of the common detritivorous insect Sericostoma pyrenaicum, matching previous results with detritivorous crustaceans such as Echinogammarus berilloni (Flores et al, 2014a) and Gammarus fossarum (Zubrod et al, 2014(Zubrod et al, , 2017. This is noteworthy because we used waterborne concentrations (0.125 and 1.25 μg L À 1 ) that were environmentally relevant and well below non-effect concentrations observed in chronic toxicity tests with microcrustacean daphnids (NOEC: 9 μg L À 1 ) (Elias and Bernot, 2014).…”

“…In our experiment, decomposition mediated by S. pyrenaicum was significantly reduced by exposure to chlorothalonil, in agreement with studies with Gammarus spp. (Dimitrov et al, 2014;Zubrod et al, 2014Zubrod et al, , 2017 and the caddisfly Chaetopteryx villosa Fabricius (Konschak et al, 2019) exposed to other fungicides, but contrasting with experiments finding no effects (Zubrod et al, 2011). The wide variety of fungicides and invertebrates used in experiments precludes any generalization currently.…”

“…The high mortality rates in our experiment obscured possible sublethal effects that might modify consumption and, therefore, litter mass loss (Flores et al, 2014a(Flores et al, , 2014b. For example, previous studies with G. fossarum found sublethal reduction in invertebrate growth due to fungicides (Zubrod et al, 2015b(Zubrod et al, , 2017.…”

“…AH assemblages are known to suffer reductions in biomass, sporulation rate and taxon richness due to fungicides (Zubrod et al, 2011(Zubrod et al, , 2015a(Zubrod et al, , 2015b(Zubrod et al, , 2017Dimitrov et al, 2014;Flores et al, 2014a). Our study supported these findings, as both exposure modes caused a large decrease in sporulation rate and taxon richness.…”

History matters: Heterotrophic microbial community structure and function adapt to multiple stressors

“…In fact, fungicides induced a community shift by replacing aquatic hyphomycete species considered as palatable for leaf‐shredding detritivores (i.e., A. acuminata and T. angulatum ; Bärlocher & Kendrick, ; Arsuffi & Suberkropp, ; Graça, Maltby, & Calow, ; Bundschuh et al., ) with less palatable species (i.e., T. marchalianum and T. setigerum ; Bärlocher & Kendrick, ; Graça et al., ; Bundschuh et al., ). Consequently, an implication in the quality of leaves as food for leaf‐shredding detritivores is probable, with potential consequences for their life‐history strategy (Zubrod et al., ). However, leaf breakdown might be increased if fungicides and nutrient enrichment stimulate the abundance and biomass production of hyphomycetes preferred by leaf‐shredding detritivores (Zubrod, Feckler, et al., ).…”