Alteration of leaf decomposition in copper contaminated freshwater mesocosms

Abstract

The influence of copper on leaf litter decomposition was examined in experimental streams. Controls and three levels of contamination (5, 25, and 75 microg/L) were tested in triplicate in 20-m-long mesocosms. Equal quantities of alder, maple, and oak leaves were enclosed in mesh bags and placed in the upper and lower mesocosm sections that exhibited different habitat characteristics (shallow with pebble substrate or deep with fine substrate and macrophytes, respectively). Decomposition rate in the upper section of the 75 micro.g/L mesocosms was significantly reduced to 28% of control values. No significant reductions in the decomposition rate were seen in the lower section. No differences in the leaf-associated mycelial biomass and sporulation rates were observed between treatments, but they were consistently higher in the upper sections. The aquatic hyphomycete community was not affected by the contamination. The abundances of total leaf-associated macroinvertebrates and the dominant shredder (Gammarus pulex) were considerably reduced in the upper sections at 75 microg/L. Therefore, the reduced leaf decomposition probably resulted from a reduction in the abundance of macroinvertebrate detritivores. In addition, local variations in physical and biological characteristics of the habitat along the mesocosms significantly influenced the effects of copper on leaf-associated decomposers.

Inorganic fungicides as routinely applied in organic and conventional agriculture can increase palatability but reduce microbial decomposition of leaf litter

“…; Duarte, Pascoal & Cássio ) may have reduced the competitive pressure for fungi resulting in the higher fungal biomasses. This may also explain the observed trends to an increased fungal spore production (Roussel, Chauvet & Bonzom ; Sridhar & Bärlocher ) and a higher number of fungal species on Cu‐exposed leaf discs (Table ). Likewise, Bundschuh et al .…”

“…), some studies assessed leaf‐associated microbial community composition and functioning in response to Cu exposure (Tattersfield ; Duarte et al . ; Roussel, Chauvet & Bonzom ; Duarte et al . ; Pradhan et al .…”

Prevalence of indirect toxicity effects of aluminium flakes on a shredder‐fungal‐leaf decomposition system

“…That the fungi in our experiment were negatively affected by the addition of Al flakes to microcosms accords with previous studies, where Al was found to affect fungal development and sporulation (Chamier et al ., ; Roussel et al ., ; Cornut et al ., ). The decline in fungal biomass contrasts, however, with the resistance of G. pulex to Al flakes.…”

“…This outcome accords with previous studies that found FR to be a robust and sensitive indicator of stressful conditions experienced by G. pulex (e.g. Forrow & Maltby, ; Maltby et al ., ; Zubrod et al ., ), including stress imposed by metal exposure (Maltby & Crane, ; Roussel et al ., ; Alonso et al ., ). Consequences at the ecosystem level, that is beyond altered FRs and other ramifications for gammarids not captured by our survival and body mass assessments, are potentially far‐reaching.…”

“…Evidence from acidic fresh waters indicates that aquatic fungi can also be impaired by elevated Al concentrations (Chamier, Sutcliffe & Lishman, ; Baudoin et al ., ) leading to reduced fungal biomass, degradative fungal activity and nutritional quality of food for Gammarus (e.g. N and P contents; Roussel, Chauvet & Bonzom, ). If the FR of gammarids declines because of reduced food quality (Maltby et al ., ), then leaf assimilation, animal growth and the production of fine‐particulate organic matter (FPOM) in the form of faeces (Joyce & Wotton, ; Yoshimura et al ., ) will diminish as well (Balseiro & Albariño, ; Navel et al ., ), suggesting a potentially broad range of indirect ecological impacts.…”