Microbial Decomposer Communities Are Mainly Structured by Trophic Status in Circumneutral and Alkaline Streams

Abstract

In streams, the release of nitrogen and phosphorus is reported to affect microbial communities and the ecological processes they govern. Moreover, the type of inorganic nitrogen (NO 3 , NO 2 , or NH 4 ) may differently impact microbial communities. We aimed to identify the environmental factors that structure aquatic microbial communities and drive leaf litter decomposition along a gradient of eutrophication. We selected five circumneutral (Portuguese) and five alkaline (French) streams differing in nutrient concentrations to monitor mass loss of alder leaves, bacterial and fungal diversity by PCR-denaturing gradient gel electrophoresis, fungal biomass and reproduction, and bacterial biomass during 11 weeks of leaf immersion. The concentrations of inorganic nutrients in the stream water ranged from 5 to 300 g liter ؊1 soluble reactive phosphorus, 0.30 to 5.50 mg liter ؊1 NO 3 -N, 2 to 103 g liter ؊1 NO 2 -N, and <4 to 7,100 g liter ؊1 NH 4 -N. Species richness was maximum in moderately anthropized (eutrophic) streams but decreased in the most anthropized (hypertrophic) streams. Different species assemblages were found in subsets of streams with different trophic statuses. In both geographic areas, the limiting nutrient, either nitrate or phosphate, stimulated the microbial activity in streams of intermediate trophic status. In the hypertrophic streams, fungal biomass and reproduction were significantly lower, and bacterial biomass dramatically decreased at the site with the highest ammonium concentration. The limiting nutrients that defined the trophic status were the main factor structuring fungal and bacterial communities, whatever the geographic area. A very high ammonium concentration in stream water most probably has negative impacts on microbial decomposer communities.

Effects of some abiotic factors on the occurrence of aquatic mycobiota in lakes of the Drawa National Park

“…Other studies on the relationships between the trophic state of water bodies and diversity of aquatic hyphomycetes only partly support the present results. Chung and Suberkropp (2008) observed an increase in species diversity in water with a higher trophic index (TI), contrary to Duarte et al (2009) who observed a decrease in fungal diversity.…”

“…Such effects can be demonstrated by studies on the effects of concentrations of inorganic nitrogen and phosphorus compounds on the diversity of aquatic mycobiota and the intensity of decomposition of organic matter by these microorganisms. According to Duarte et al (2009), the greatest diversity of mycobiota was observed in mesotrophic conditions, while reduced biomass and diversity of mycobiota were noted in hypertrophic conditions. Chung and Suberkropp (2008) showed, however, that biomass, diversity and sporulation intensity were greater in water with higher nitrogen and phosphorus levels than in the control.…”

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…”

“…16S rDNA (V6-to-V8) Das et al, 2007;Duarte et al, 2009aDuarte et al, , 2010 Table 1. Primers used to assess diversity of fungi and bacteria associated with plant litter in freshwaters.…”

“…Bacteria are also able to produce enzymes that degrade the polysaccharides of plant litter (Burns, 1982), but its contribution to plant litter decomposition in streams appears to be lower than that of fungi, as assessed from microbial biomass and productivity (e.g. Baldy et al, 2002;Duarte et al, 2009a;Hieber & Gessner, 2002;Pascoal & Cássio, 2004). The lower contribution of bacteria to leaf decomposition can be related to the lack of invasive ability, which confines bacteria to leaf surfaces.…”