Structure of Microbial Communities in Sphagnum Peatlands and Effect of Atmospheric Carbon Dioxide Enrichment

Abstract

Little is known about the structure of microbial communities in Sphagnum peatlands, and the potential effects of the increasing atmospheric CO2 concentration on these communities are not known. We analyzed the structure of microbial communities in five Sphagnum-dominated peatlands across Europe and their response to CO2 enrichment using miniFACE systems. After three growing seasons, Sphagnum samples were analyzed for heterotrophic bacteria, cyanobacteria, microalgae, heterotrophic flagellates, ciliates, testate amoebae, fungi, nematodes, and rotifers. Heterotrophic organisms dominated the microbial communities and together represented 78% to 97% of the total microbial biomass. Testate amoebae dominated the protozoan biomass. A canonical correspondence analysis revealed a significant correlation between the microbial community data and four environmental variables (Na +, DOG, water table depth, and DIN), reflecting continentality, hydrology, and nitrogen deposition gradients. Carbon dioxide enrichment modified the structure of microbial communities, but total microbial biomass was unaffected. The biomass of heterotrophic bacteria increased by 48%, and the biomass of testate amoebae decreased by 13%. These results contrast with the absence of overall effect on methane production or on the vegetation, but are in line with an increased below-ground vascular plant biomass at the same sites. We interpret the increase in bacterial biomass as a response to a CO2induced enhancement of Sphagnum exudation. The causes for the decrease of testate amoebae are unclear but could indicate a top-down rather than a bottom-up control on their density.

Evolutionary and ecophysiological significance of sugar utilization by the peat moss Sphagnum compactum (Sphagnaceae) and the common charophycean associates Cylindrocystis brebissonii and Mougeotia sp. (Zygnemataceae)

“…For example, glucose is known to attract motile hormogonia of the nitrogen-fi xing cyanobacterium Nostoc , which subsequently takes up symbiotic residence within the tissues of various land plants ( Nilsson et al, 2006 ). The N 2 -fi xing cyanobacteria Nostoc , Anabaena , Tolypothrix , and Stigonema are common peat moss associates ( Basilier, 1980 ;Hingley, 1993 ;Mitchell et al, 2003 ), andBasilier (1980) demonstrated that nitrogen compounds produced and exuded by N. muscorum Allison are absorbed by Sphagnum and transported upward in the stem. Ecological theory predicts that plants of infertile sites should use exudates to foster the growth of microbes that provide scarce nutrients ( Paterson et al, 2006 ).…”

“…A second goal was to obtain insight into the ecological roles of mixotrophy in bryophytes and charophyceans. To accomplish this, we quantitatively analyzed the growth responses to exogenous sugar of two representatives of Zygnematales, a relatively early-diverging charophycean lineage recognized for high diversity and abundance in peatlands and associated humic lakes (Graham and Wilcox, 2000;Mitchell et al, 2003), and Sphagnum compactum Lam. & DC, a representative emergent peat moss species whose compact structure facilitates physiological study in the laboratory.…”

Stable isotope analyses revealed high seasonal dynamics in the food web structure of a peatbog

“…In peatbogs, testate amoebae represent an ideal model group for microbial food web studies owing to their abundance, diversity and ubiquity (Jassey et al, ). Due to the clear predominance of testate amoebae in peatbogs, they are recognised as having the most important role in matter and energy flow (Mitchell et al, ; Nguyen‐Viet et al, ). These protozoans are significant consumers of bacteria, flagellates and algae, and participate in mineralisation of organic matter and circulation of biogenic compounds (Gilbert et al, ; Wilkinson and Mitchell, ; Mieczan et al, ).…”

Cut‐over peatland regeneration assessment using organic matter and microbial indicators (bacteria and testate amoebae)

“…Indeed, the physiochemical and botanical properties of the underlying peat have been shown to affect strongly (i) the growth of Sphagnum mosses (Grosvernier, Matthey & Buttler 1997; Buttler, Grosvernier & Matthey 1998) and (ii) gas fluxes to the atmosphere (Buttler, Dinel & Lévesque 1994; Charman, Aravena & Warner 1994) while microbial communities have been shown to respond to ecological gradients as well as ecosystem perturbations, such as nitrogen input and elevated atmospheric CO 2 concentrations (Gilbert et al . 1998a,b; Mitchell et al . 2003).…”