Effects of Cadmium and Phenanthrene Mixtures on Aquatic Fungi and Microbially Mediated Leaf Litter Decomposition

Abstract

Urbanization and industrial activities have contributed to widespread contamination by metals and polycyclic aromatic hydrocarbons, but the combined effects of these toxics on aquatic biota and processes are poorly understood. We examined the effects of cadmium (Cd) and phenanthrene on the activity and diversity of fungi associated with decomposing leaf litter in streams. Leaves of Alnus glutinosa were immersed for 10 days in an unpolluted low-order stream in northwest Portugal to allow microbial colonization. Leaves were then exposed in microcosms for 14 days to Cd (0.06-4.5 mg L(-1)) and phenanthrene (0.2 mg L(-1)) either alone or in mixture. A total of 19 aquatic hyphomycete species were found sporulating on leaves during the whole study. The dominant species was Articulospora tetracladia, followed by Alatospora pulchella, Clavatospora longibrachiata, and Tetrachaetum elegans. Exposure to Cd and phenanthrene decreased the contribution of A. tetracladia to the total conidial production, whereas it increased that of A. pulchella. Fungal diversity, assessed as denaturing gradient gel electrophoresis fingerprinting or conidial morphology, was decreased by the exposure to Cd and/or phenanthrene. Moreover, increased Cd concentrations decreased leaf decomposition and fungal reproduction but did not inhibit fungal biomass production. Exposure to phenanthrene potentiated the negative effects of Cd on fungal diversity and activity, suggesting that the co-occurrence of these stressors may pose additional risk to aquatic biodiversity and stream ecosystem functioning.

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

“…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…”

“…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).…”

“…Indeed, multivariate analysis based on fungal and bacterial fingerprints proved to be an useful tool to detect shifts in the structure of aquatic microbial communities exposed to anthropogenic stressors in microcosms, such as metals ions alone or in mixtures (e.g. Duarte et al, 2008bDuarte et al, , 2009bMedeiros et al, 2011), metal nanoparticles (Pradhan et al, 2011), mixtures of metals and nutrients (Fernandes et al, 2009), and mixtures of metals and polycyclic aromatic hydrocarbons (PAHs) (Moreirinha et al, 2011). Temperature gradient gel electrophoresis (TGGE), whose principle is very similar to that of DGGE, but instead of a chemical gradient is used a temperature gradient in the gel, was also successfully applied to monitor fungal communities structure in harsh environments such as groundwater wells and heavily polluted surface waters (Solé et al, 2008).…”

“…Several authors use the relative surface of each band in the profile (Pi) as a proxy of the relative frequency of each taxon (e.g. Duarte et al, 2009a;Moreirinha et al, 2011;Sridhar et al, 2009) that can be estimated as follows (1):…”

“…Duarte et al, 2008bDuarte et al, , 2009bDuarte et al, , 2010Fernandes et al, 2009;Medeiros et al, 2010) and ordination analyses (e.g. Duarte et al, 2009a;Moreirinha et al, 2011;Sridhar et al, 2009). …”