Pietikäinen, J., Kiikkilä, O. and Fritze, H. 2000. Charcoal as a habitat for microbes and its effect on the microbial community of the underlying humus. -Oikos 89: 231-242.Wildfires produce a charcoal layer, which has an adsorbing capacity resembling activated carbon. After the fire a new litter layer starts to accumulate on top of the charcoal layer, which liberates water-soluble compounds that percolate through the charcoal and the unburned humus layer. We first hypothesized that since charcoal has the capacity to adsorb organic compounds it may form a new habitat for microbes, which decompose the adsorbed compounds. Secondly, we hypothesized that the charcoal may cause depletion of decomposable organic carbon in the underlying humus and thus reduce the microbial biomass. To test our hypotheses we prepared microcosms, where we placed non-heated humus and on top one of the adsorbents: non-adsorptive pumice (Pum), charcoal from Empetrum nigrum (Em-pCh), charcoal from humus (HuCh) or activated carbon (ActC). We watered them with birch leaf litter extract. The adsorbing capacity increased in the order Pum B HuChB EmpChBActC, the adsorbents being capable of removing 0%, 26%, 42% and 51% of the dissolved C org in the litter extract, respectively. After one month, all adsorbents harboured microbes, but their amount and basal respiration was largest in EmpCh and HuCh, and smallest in Pum. In addition, different kinds of microbial communities with respect to their phospholipid fatty acid and substrate utilization patterns were formed in the adsorbents. The amount of microbial biomass and number of bacteria did not differ between humus under different adsorbents, although different microbial communities developed in humus under EmpCh compared with Pum, which is obviously related to the increased pH of the humus under EmpCh, and also ActC. We suggest that charcoal from burning can support microbial communities, which are small in size but have a higher specific growth rate than those of the humus. Although the charcoal layer induces changes in the microbial community of the humus, it does not reduce the amount of humus microbes.

Nitrogen (N) accumulation rates in peatland ecosystems indicate significant biological atmospheric N 2 fixation associated with Sphagnum mosses. Here, we show that the linkage between methanotrophic carbon cycling and N 2 fixation may constitute an important mechanism in the rapid accumulation of N during the primary succession of peatlands. In our experimental stable isotope enrichment study, previously overlooked methane-induced N 2 fixation explained more than one-third of the new N input in the younger peatland stages, where the highest N 2 fixation rates and highest methane oxidation activities co-occurred in the water-submerged moss vegetation.P eat-accumulating wetlands, i.e., peatlands, store approxi-

Soil bacterial biomass, phospholipid fatty acid pattern, pH tolerance, and growth rate were studied in a forest area in Finland that is polluted with alkaline dust from an iron and steel works. The pollution raised the pH of the humus layer from 4.1 to 6.6. Total bacterial numbers and the total amounts of bacterial phospholipid From each site, 10 individual core samples (AO1/A02 layer) were combined into a bulk sample. The 20 bulk soil samples were then sieved (mesh size, 4 mm), and visible plant 4026 on July 16, 2020 by guest http://aem.asm.org/ Downloaded from

Peatlands are a major natural source of atmospheric methane (CH4). Emissions from Sphagnum-dominated mires are lower than those measured from other mire types. This observation may partly be due to methanotrophic (i.e., methane-consuming) bacteria associated with Sphagnum. Twenty-three of the 41 Sphagnum species in Finland can be found in the peatland at Lakkasuo. To better understand the Sphagnum-methanotroph system, we tested the following hypotheses: (1) all these Sphagnum species support methanotrophic bacteria; (2) water level is the key environmental determinant for differences in methanotrophy across habitats; (3) under dry conditions, Sphagnum species will not host methanotrophic bacteria; and (4) methanotrophs can move from one Sphagnum shoot to another in an aquatic environment. To address hypotheses 1 and 2, we measured the water table and CH4 oxidation for all Sphagnum species at Lakkasuo in 1-5 replicates for each species. Using this systematic approach, we included Sphagnum spp. with narrow and broad ecological tolerances. To estimate the potential contribution of CH4 to moss carbon, we measured the uptake of delta13C supplied as CH4 or as carbon dioxide dissolved in water. To test hypotheses 2-4, we transplanted inactive moss patches to active sites and measured their methanotroph communities before and after transplantation. All 23 Sphagnum species showed methanotrophic activity, confirming hypothesis 1. We found that water level was the key environmental factor regulating methanotrophy in Sphagnum (hypothesis 2). Mosses that previously exhibited no CH4 oxidation became active when transplanted to an environment in which the microbes in the control mosses were actively oxidizing CH4 (hypothesis 4). Newly active transplants possessed a Methylocystis signature also found in the control Sphagnum spp. Inactive transplants also supported a Methylocystis signature in common with active transplants and control mosses, which rejects hypothesis 3. Our results imply a loose symbiosis between Sphagnum spp. and methanotrophic bacteria that accounts for potentially 10-30% of Sphagnum carbon.

The main objectives of this study were to uncover the pathways used for methanogenesis in three different boreal peatland ecosystems and to describe the methanogenic populations involved. The mesotrophic fen had the lowest proportion of CH 4 produced from H 2 -CO 2 . The oligotrophic fen was the most hydrogenotrophic, followed by the ombrotrophic bog. Each site was characterized by a specific group of methanogenic sequences belonging to Methanosaeta spp. (mesotrophic fen), rice cluster-I (oligotrophic fen), and fen cluster (ombrotrophic bog).Northern peatlands are important emitters of the green house gas methane (CH 4 ) produced by methanogenic archaea (3,18,30). Methanogens utilize a limited number of substrates, the most important of which are acetate and H 2 -CO 2 (38). In peatlands, H 2 -CO 2 -dependent methanogenesis is thought to be the main pathway for CH 4 production (20,21,26,37), but in some minerotrophic peatlands (fens), acetoclastic methanogenesis is often predominant in upper peat layers (4,23,31). The diversity of methanogenic communities of fen (15, 17) and bog (2, 16, 35) ecosystems has recently been described, but data on the combined investigation of methanogenic pathways and methanogen populations are scarce. To the best of our knowledge, community studies have never been associated with the detection of methanogenic pathways in fen ecosystems, and only one study of an acidic bog ecosystem has been published (20). The aim of our study was to determine the precursors used for methanogenesis in three peatland ecosystems (a mesotrophic fen, an oligotrophic fen, and an ombrotrophic bog) and to describe the diversity of methane-producing archaea by using molecular methods that target the functional methyl coenzyme M reductase gene (mcrA).Replicate samples from depths with the highest potential CH 4 production rates were taken from a mesotrophic fen, an oligotrophic fen, and an ombrotrophic bog at the Lakkasuo mire complex in central Finland (61°48ЈN, 24°19ЈE) in August 2003. The fraction of CH 4 produced from H 2 -CO 2 was estimated at each site by a tracer experiment (8, 11) and by the inhibition of acetoclastic methanogenesis with CH 3 F (methyl fluoride) (6,14,22). The Gibbs free energy (⌬G) of H 2 -dependent methanogenesis was calculated (10, 12), and potential CH 4 production was measured as described earlier (17). Fatty acids and alcohols dissolved in the pore water were analyzed by high-pressure liquid chromatography (25). All experiments were conducted on triplicate samples from each peat ecosystem. DNA was extracted directly from peat samples (17), and a portion of the methanogen-specific mcrA was amplified with the primer pair ML (28). Clone libraries were subjected to restriction fragment length polymorphism (RFLP) analysis with the restriction enzymes MspI and TaqI, and representatives of the biggest RFLP groups were sequenced for phylogenetic analysis.The contributions of H 2 -CO 2 -dependent methanogenesis to total CH 4 production varied clearly among the three peatland ecosystems (...