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Although this may have been due to the relatively low detected richness level relative to Morales et al. Little is known about the role of fungi in peatlands, but diverse communities have been found beneath the Sphagnum mat and in close association with ericaceous shrubs Thormann, ; Artz et al. Fungi are generally thought to predominate in peatland lawns and hummocks Jaatinen et al. Thus it was interesting that most fungal taxa were identified at all three depths among the three JBL peatlands. Fungi are typically most competitive under an oxic environment, however they can carry out fermentation.
So their abundance at depth may in part be due to a lack of alternative inorganic electron acceptors e. This might also imply that facultative fungi supply fermentation products that ultimately fuel methanogenesis Conrad, Consistent with prior studies, microbial biomass decreased with depth probably due to the presence of more labile organic matter and higher redox states typically found near the surface of peat profiles Blodau and Moore, ; Blodau et al.
Although microbial biomass across sites was generally quite small compared to other bogs and fens Moore and Basiliko, , it was similar to that in mined peatlands in more southern regions of Canada that have relatively low nutrient and carbon availability Basiliko et al. Bacteria often predominate in deeper more anoxic peat layers as they can utilize alternative electron acceptors Killham and Prosser, Microbial biomass did not correlate with potential CO 2 production rates in contrast to previous studies Blodau et al.
However, this may simply reflect the low microbial biomass and low amount of labile carbon in our sites. Despite the similarity of the microbial communities among the three peatlands, there were differences in basal respiration, initial enzyme activities and substrate utilization patterns. Greater microbial activity was observed in the fen compared to the bogs, possibly due to the higher in situ nutrient concentrations and greater carbon substrate availability typically found in fens Moore and Basiliko, ; Knorr and Blodau, Overall the average oxic SIR ratio response was very similar among deep peat samples in all three peatlands and greater than those in both the surface and middle peat samples.
Deeper peat is older and typically has lower levels of labile carbon Glatzel et al. Thus, the microbial community at these depths was probably substrate limited relative to the surface peat. However, this trend disappeared in the anoxic SIR assay, as there was little difference in the response among depths between Kinoje and Victor bogs. In contrast, Victor Fen had greater average SIR values in the surface peat sample, likely as a result of higher redox substrate concentrations Knorr and Blodau, ; Webster and McLaughlin, This apparent contradiction between microbial activity and community composition may be explained by differences in peat organic matter quality.
Plant litter from bogs and fens have different nutrient concentrations Bragazza et al. Similar to our study the authors reported higher enzyme activities in peat composed of vascular plants, typical in fens, rather than Sphagnum dominated peat and also failed to identify a strong relationship between microbial community composition and EEA. Moreover, the differences in SIR activities, identified by the NMDS ordination, among sites was primarily due to the magnitude of the response, but the relative substrate utilization patterns i. Furthermore, vegetation type has been shown to influence microbial activity more than water table drawdown Trinder et al.
The relatively high N -acetyl-beta- D -glucosaminidase activity throughout the peat profile suggests a high metabolic demand for N released during chitin turnover Sinsabaugh et al. This contradicts our previous finding that carbon:nitrogen ratio decreases with depth and might represent bacterial dominance of decomposition due to higher N demand.
However, it is not certain whether fungi or bacteria produced these enzymes or what the specific activity of the fungi is in deep peat. Interestingly, a recent meta-analysis found that shifts in bacterial to fungal dominance across environmental gradients often do not correlate with changes in element cycling and may be due to niche overlap between fungal and bacterial communities Strickland and Rousk, In an antibiotic inhibition assay, Winsborough and Basiliko showed that bacteria dominated peatland microbial activity; while fungal activity did increase in acidic dry bogs it was still lower than bacterial activity.
Although we do not have direct measurements of fungal biomass, these results suggest that our understanding of the relationship between fungi and ecosystem function in peat soil is incomplete. We did not find a relationship between microbial community composition and activities in contrast to our hypothesis.
Although this could be due to the issues of the taxa-level resolution using T-RFLP small-subunit rDNA, this finding highlights the importance of carbon substrate as a proximate control of microbial community dynamics because similar communities can perform different functions given different resources and conditions. As predicted and consistent with previous studies Moore and Dalva, ; Updegraff et al. However, CO 2 production did not correlate with enzyme activity probably because the enzymes measured in this study may only be a subset of those actually involved in peat decomposition Horwath, Potential CO 2 production rates among the depths were lower in anoxic conditions but there was a strong correlation between oxic and anoxic CO 2 production consistent with previous investigations Moore and Dalva, ; Yavitt et al.
These findings suggest that similar peat properties control the activities of both aerobic and anaerobic microbial metabolism Glatzel et al. Similarly, CH 4 production rates were low throughout the peat profile but still within the range of previously reported values Moore and Dalva, ; Glatzel et al.
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Microbial community composition was very similar among peatlands and at depths within the JBL despite differences in geographic location and nutrient status. In contrast, microbial activity appears to be determined by the quality of the peat substrate and the presence of potential microbial inhibitors.
Spatially-integrated estimates of net ecosystem exchange and methane fluxes from Canadian peatlands
As climate change is expected to cause a shift in JBL plant community composition, this study suggests that the microbial community will respond quickly to changes in plant litter and root exudate quality but the existing peat substrate will probably have a large influence on future microbial activity. For example, a shift from Sphagnum to sedge-dominated peatlands may not necessarily result in the expected increase in carbon mineralization due to the antimicrobial properties of the Sphagnum -peat. Interestingly, we identified fungal taxa in deep peat but it is unclear what anaerobic processes are occurring and how these organisms influence carbon cycling.
Thus, more in depth profiling of the JBL microbial community and identification of the potential constraints on microbial activity is required in order to better predict future peatland carbon dynamics. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
The authors gratefully acknowledge Benoit Hamel, Mark Crofts, and Adam Kinnunen for collection of peat samples, Varun Gupta and Charlotte Hewins for assistance with laboratory analyses and the two reviewers for comments and suggestions to improve the manuscript.
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