Effects of Experimental Lead Pollution on the Microbial Communities Associated with Sphagnum fallax (Bryophyta)

Abstract

Ecotoxicological studies usually focus on single microbial species under controlled conditions. As a result, little is known about the responses of different microbial functional groups or individual species to stresses. In an aim to assess the response of complex microbial communities to pollution in their natural habitat, we studied the effect of a simulated lead pollution on the microbial community (bacteria, cyanobacteria, protists, fungi, and micrometazoa) living on Sphagnum fallax. Mosses were grown in the laboratory with 0 (control), 625, and 2,500 mg L _ 1 of Pb 2+ diluted in a standard nutrient solution and were sampled after 0, 6, 12, and 20 weeks. The biomasses of bacteria, microalgae, testate amoebae, and ciliates were dramatically and significantly decreased in both Pb addition treatments after 6, 12, and 20 weeks in comparison with the control. The biomass of cyanobacteria declined after 6 and 12 weeks in the highest Pb treatment. The biomasses of fungi, rotifers, and nematodes decreased along the duration of the experiment but were not significantly affected by lead addition. Consequently, the total microbial biomass was lower for both Pb addition treatments after 12 and 20 weeks than in the controls. The community structure was strongly modified due to changes in the densities of testate amoebae and ciliates, whereas the relative contribution of bacteria to the microbial biomass was stable. Differences in responses among the microbial groups suggest changes in the trophic links among them. The correlation between the biomass of bacteria and that of ciliates or testate amoebae increased with increasing Pb loading. We interpret this result as an effect on the grazing pathways of these predators and by the Pb effect on other potential prey (i.e., smaller protists). The community approach used here complements classical ecotoxicological studies by providing clues to the complex effect of pollutant-affecting organisms both directly and indirectly through trophic effects and could potentially find applications for pollution monitoring.

Ecology of testate amoebae (Protists) inSphagnumpeatlands of eastern Poland: Vertical micro-distribution and species assemblages in relation to environmental parameters

“…Their well-defined ecological preferences in relation to important ecological variables in peatlands have made them useful in ecological studies (Charman, 1997). Testate amoebae are excellent indicators of calcite precipitation in lakes (Casper and Scho¨nborn, 1985) and heavy metal pollutants in peatlands (Nguyen-Viet et al, 2007). Previous studies have shown that the abundance of each taxon, and hence the structure of communities, are controlled by a set of environmental variables.…”

“…In addition, factors such as light, oxygen and food availability may also affect testate amoebae communities (Charman et al, 2000). The ecology of most species is still rather poorly known although there have been a number of recent studies in several regions of the world, including New Zealand (Charman, 2001), north-western Poland (Lamentowicz and Mitchell, 2005), Alaska (Payne et al, 2006), and in France (Nguyen-Viet et al, 2007). Several authors have studied the vertical micro-distribution of testate amoebae in peatlands.…”

Ecology of testate amoebae (Protists) in mosses: distribution and relation of species assemblages with environmental parameters (King George Island, Antarctica)

“…Testate amoebae form a very sensitive group of organisms (Nguyen-Viet et al 2007). Their short generation times make them useful indicators of environmental changes (Vincke et al 2004a, b;Mattheeussen et al 2005).…”

Using “bryophytes and their associated testate amoeba” microsystems as indicators of atmospheric pollution

“…The TA community was extracted from the mosses using the method described by Nguyen-Viet et al (2007b) and Meyer et al (2010a,b): each sample was first shaken in a vortex and then filtered through a 180 m mesh filter. Fifteen mL of glutaraldehyde (2% final concentration) were added to the sample.…”