Michael Preston (Department of Geography)

Abstract for Oral Presentation at 2011 CSM Conference:

Disparate decomposer communities across peatland types exhibit functional redundancy

M.D. Preston¹, K. Haynes^1,2, J. McLaughlin³, K. Webster⁴ and N. Basiliko<sup>1

1</sup> Department of Geography, University of Toronto Mississauga, Mississauga, Ontario, L5L 1C6
² Department of Physical and Environmental Sciences, University of Toronto Scarborough, Toronto, Ontario, M1C 1A4
³ Ontario Forest Research Institute, Sault Ste. Marie, Ontario, P6A 2E5
⁴ Canadian Forest Service, Sault Ste. Marie, Ontario, P6A 2E5


Northern peatlands are large repositories of atmospheric carbon due to a relative imbalance between production and microbial decomposition. Future climate scenarios predict large changes in temperature and precipitation patterns that will probably result in shifts in the peatland plant community composition and thus change the quality of the litter received by the soil microbial community. Little is known about the effect of a change in carbon substrate quality on peatland microbial activity including the production of carbon dioxide (CO₂). Although most ecosystem models assume that microbial communities in similar environments are also functionally analogous, studies are beginning to emerge that suggest various soil microbial communities respond to litter quality differently in terms of rates of carbon cycling. Peat soils were collected from three hydrologically distinct fens (rich fen, pH 6.7; intermediate fen pH 5.4; and a poor fen pH 4.3), which differed in their trophic status and dominant vegetation, near White River, Ontario. Five within-site replicates of surface peat were collected from each fen along a 100-m transect in May and August 2009. Substrate mineralization rates were characterized for each peat soil in laboratory microcosms under both aerobic and anaerobic conditions using ten organic substrates. Six synthetic (glucose, cellulose, p-coumaric acid, sodium benzoate, lignin and a mixture of amino acids) and four natural extracts taken from plants in the three fens (two sedge and two Sphagnum species) were added to peat soil (1 mg C ml^-1) and CO₂ production was monitored over time. We predicted that complex substrates would be preferentially utilized in the poor fen and relatively simple substrates in the rich fen. The relative ability of the peat soil microorganisms to mineralize substrates in the short term was similar across sites and within sites and generally was independent of sampling time and oxygen conditions. There was no preferential mineralization of (i) chemically complex substances in the poor fen, (ii) simple compounds in the rich fen, or (iii) organic matter native to each site by the microbial community as hypothesized. Moreover, molecular fingerprinting (T-RFLP of SSU rDNA) of bacterial and fungal communities revealed distinct decomposer communities within each site. Thus these findings suggest there may be some functional redundancy across peatland microbial communities and that these communities will be able to respond rapidly in terms of organic matter substrate mineralization to future environmental changes, which will have implications on global climate feedback effects.