Response of Aquatic Hyphomycete Communities to Changes in Heavy Metal Exposure

Abstract

Decomposition of Alnus glutinosa (alder) leaves was studied in a severely (site H4) and a moderately (site H8) heavy metal polluted stream in the former copper shale mining district of Mansfeld, Central Germany. Leaves at H8 had reduced fungal diversity and spore production but a high exponential decay rate (k = 0.065). No further mass loss of leaves occurred at H4 after 4 -6 weeks, and fungal diversity and spore production were lower than in H8. Decay and sporulation rates gradually increased to values of H8 control leaves in leaves preincubated in H4 and then transferred to H8. These increases correlated with the invasion of transplanted leaves by Tetracladium marchalianum and Tricladium angulatum. In the reverse transplant experiment (H8 to H4), mass loss appeared to stop immediately. Sporulation rates also declined, but remained consistently above levels in H4 control leaves. Leaves precolonized in the laboratory by one of three aquatic hyphomycete species exhibited increased decay rates in both streams. Sporulation rates on these leaves were greater than those of control leaves in H4, but smaller than those of control leaves in H8. IntroductionAquatic hyphomycetes, an ecologically defined group of asexually reproducing fungi, play a crucial role in the decomposition and transformation of leaves and other allochthonous plant material in streams (BÄRLOCHER, 1992a;CAI et al., 2003; TSUI and HYDE, 2003). Fungal biomass on newly exposed leaves increases to a peak (up to 17% of detrital dry mass, GESSNER, 1997) within a few weeks. It remains at this level for some time before gradually declining. In addition to increasing their mycelial biomass, the fungi release large numbers of conidia (up to 8 µg -1 detrital mass; GESSNER, 1997). Generally, more than 90% of all conidia released on any given date belong to 1-4 species (BÄRLOCHER, 1992b). There is some evidence of species replacement: certain species may be selectively inhibited or favoured by seasonal changes in temperature (WEBSTER et al., 1976;SUBERKROPP, 1984), or an extended residence time may allow a substrate to accumulate more rare species (BÄR-LOCHER, 1980). More commonly, the fungal community changes because of shifts in the relative frequencies of occurrence of species that arrive early and persist throughout the leaf's decay. This underlines the importance of early resource capture, confirmed by stream expo-

Effects of Zn, Fe and Mn on Leaf Litter Breakdown by Aquatic Fungi: a Microcosm Study

“…Even though leaf decomposition was reduced by exposure to Zn alone (DUARTE et al, 2004) with Cu (DUARTE et al, 2008), there is evidence of fungal acclimation to these metals (DUARTE et al, 2009). Other studies reveal that rates of litter decomposition are generally low in waters affected by mine drainage (BERMINGHAM et al, 1996;NIYOGI et al, 2001NIYOGI et al, , 2002aSRIDHAR et al, 2001SRIDHAR et al, , 2005. Therefore, the effects of mine drainage on litter decomposition cannot be generalized probably due to site-specific environmental conditions or to the adaptation of fungal communities.…”

“…Pollution is likely to lower biodiversity of aquatic hyphomycetes (by eliminating sensitive species) and the ecological processes they perform. In general, heavy metals depress fungal productivity (DUARTE et al, 2004), reproduction (DUARTE et al, 2004;SRIDHAR et al, 2001) and diversity (SRIDHAR et al, 2005;NIYOGI et al, 2002b) delaying plant litter decomposition (DUARTE et al, 2004;SRIDHAR et al, 2005). Moreover, short-term effects of metal mixtures on microbial decomposition of leaf litter were reported to be mostly additive (DUARTE et al, 2004).…”

The Role of Early Fungal Colonizers in Leaf‐Litter Decomposition in Portuguese Streams Impacted by Agricultural Runoff

“…Nevertheless, these transplantation experiments gave variable results that appear to be dependent on water chemistry and the initial fungal community (ROSSET and BÄRLOCHER, 1985;SUBERKROPP and CHAUVET, 1995;SRIDHAR et al, 2005). For example, fungal communities did not change when leaves colonized in a nutrient enriched stream were transplanted to a nutrient poor stream, but in the reverse experiment the initial community was rapidly replaced by the indigenous one (SUBERKROPP and CHAUVET, 1995).…”

“…The transfer of colonized leaf litter from one stream to another with contrasting water chemistry has been used as an useful approach to measure how aquatic hyphomycetes react to sudden alterations in their habitat condition (SUBERKROPP and CHAUVET, 1995;SRIDHAR et al, 2005;DUARTE et al, 2008). Nevertheless, these transplantation experiments gave variable results that appear to be dependent on water chemistry and the initial fungal community (ROSSET and BÄRLOCHER, 1985;SUBERKROPP and CHAUVET, 1995;SRIDHAR et al, 2005).…”

Copper and zinc affect the activity of plasma membrane H+-ATPase and thiol content in aquatic fungi

“…Amongst fungi, aquatic hyphomycetes appear to have the greatest ecological role as decomposers of plant detritus in streams (Baldy et al, 2002; Pascoal & Cássio, 2004). Even though metal pollution lowers the biodiversity and activity of aquatic hyphomycetes, the occurrence of these groups of fungi has been consistently reported in metal-polluted streams (Pascoal et al, 2005a;Sridhar et al, 2005). This means that fungi, similar to other living organisms, have to tightly regulate the intracellular metal concentration in such a way that safe uptake of the required metal ions in the cytosol and organelles can occur without cellular damage due to metal toxicity (Kneer et al, 1992).…”