Copper and zinc mixtures induce shifts in microbial communities and reduce leaf litter decomposition in streams

Abstract

1. To assess the impact of metal mixtures on microbial decomposition of leaf litter, we exposed leaves previously immersed in a stream to environmentally realistic concentrations of copper (Cu) and zinc (Zn) (three levels), alone and in all possible combinations. The response of the microbial community was monitored after 10, 25 and 40 days of metal exposure by examining leaf mass loss, fungal and bacterial biomass, fungal reproduction and fungal and bacterial diversity. 2. Analysis of microbial diversity, assessed by denaturing gradient gel electrophoresis and identification of fungal spores, indicated that metal exposure altered the structure of fungal and bacterial communities on decomposing leaves. 3. Exposure to metal mixtures or to the highest Cu concentration significantly reduced leaf decomposition rates and fungal reproduction, but not fungal biomass. Bacterial biomass was strongly inhibited by all metal treatments. 4. The effects of Cu and Zn mixtures on microbial decomposition of leaf litter were mostly additive, because observed effects did not differ from those expected as the sum of single metal effects. However, antagonistic effects on bacterial biomass were found in all metal combinations and on fungal reproduction in metal combinations with the highest Cu concentrations, particularly at longer exposure times.

Denaturing Gradient Gel Electrophoresis (DGGE) in Microbial Ecology - Insights from Freshwaters

“…Duarte et al, 2008aDuarte et al, , 2009aFernandes et al, 2009;Moreirinha et al, 2011;Pradhan et al, 2011). For instance, DGGE proved to be a good alternative to assess fungal diversity because it is able to show several OTUs when the number of fungal reproductive structures was very low or almost absent after exposure to stressors (Duarte et al, 2008b(Duarte et al, , 2009bMedeiros et al, 2010;Moreirinha et al, 2011;Pradhan et al, 2011).…”

“…18S rDNA (5' portion) Das et al, 2007;Duarte et al, 2010;MilleLindblom et al, 2006;Nikolcheva et al, 2003 ITS3GC(F)/ITS4(R) ITS Duarte et al, 2008bDuarte et al, , 2009aDuarte et al, ,b, 2010Duarte et al, , 2011Fernandes et al, 2009;Medeiros et al, 2010;Moreirinha et al, 2011;Nikolcheva & Bärlocher, 2004, 2005Pascoal et al, 2010;Pradhan et al, 2011;Raviraja et al, 2005; 2009 Bacteria…”

“…16S rDNA (V3) Duarte et al, 2008bDuarte et al, , 2009bDuarte et al, , 2010Duarte et al, , 2011Pradhan et al, 2011 357GC(F)…”

“…Specifically, for assessing bacterial communities on decomposing plant-litter in freshwaters, primers targeting the V3 region (e.g. 338GC/518) (Duarte et al, 2008b(Duarte et al, , 2009bPradhan et al, 2011) and the V6-to-V8 regions (e.g. 984GC/1378) have been widely used (Das et al, 2007;Duarte et al, 2009aDuarte et al, , 2010 (Table 1).…”

Response variable selection in principal response curves using permutation testing

“…It estimates differences among treatments on a collection of RVs over time and the extent to which the response of those individual RVs resembles the overall response. PRC has been widely applied in aquatic ecology and ecotoxicology (e.g., Hartgers et al 1998;Cuppen et al 2000;Roessink et al 2006;Duarte et al 2008;Verdonschot et al 2015), terrestrial ecology and ecotoxicology (e.g., Heegaard and Vandvik 2004;Pakeman 2004;Britton and Fisher 2007;Moser et al 2007), microbiology (e.g., Andersen et al 2010;Fuentes et al 2014) and soil science (e.g., Kohler et al 2006;Cardoso et al 2008).…”