An Analysis of Respiratory Activity, Q 10 , and Microbial Community Composition of Soils from High and Low Tussock Sites at Toolik, Alaska O. ROGER ANDERSON Department of Biology, Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York 10964 ABSTRACT. High latitude microbial communities, incurring increased global warming, are a potential major source of respiratory CO 2 contributing to an enhanced greenhouse effect. Data on respiration and microbial density are presented for a moist, high tussock site compared with a low, water saturated site. The density of bacteria and eukaryotic microbes was nearly equivalent at both sites and potentially could yield substantial release of respiratory CO 2 with continued warming. Respiratory rates for soil from the high site were greater than the low. The Q 10 of 2.4 for the high tussock sample was approximately 1.3  that of the low site sample (Q 10 of 1.7). Key Words. Atmospheric carbon dioxide, bacterial densities, eukaryotic microbe densities, global warming, tundra soil respiration. W ITH increasing evidence of global warming (Solomon et al. 2007), as predicted earlier (e.g. Broecker 1975), there is growing concern that high-latitude terrestrial microbes within vast geographic tracts may become increasingly active resulting in greater efflux of respiratory CO 2 to the atmosphere, thus exacer- bating the greenhouse effect (Billings et al. 1982; Oberbauer et al. 1992; Raich and Schlesinger 1992; Rustad et al. 2001). This is particularly the case if high-latitude, water-saturated, anaerobic soils become warmer and drier, thus enhancing aerobic respiration (Oberbauer et al. 1992). Although soil respiration rates, and to a lesser extent Q 10 measurements, have been made at various lo- cales worldwide (e.g. Raich and Schlesinger 1992), there are fewer studies at high latitudes (e.g. Anderson 2008, 2010; Bekku et al. 2003) and no published studies apparently have examined soil respiration and Q 10 in the context of the abundance of mi- crobial taxa at high latitudes. This is the first report of respiratory activity, Q 10 , and their relationship to densities of bacteria and some protists at a tundra site in Alaska. MATERIALS AND METHODS Surface soil samples (24 1C when collected, minimum temper- ature that day 20 1C) were collected in late July 2009, from a moist high tussock site (68137 0 25.69 00 N, 149136 0 35.72 00 W) and a water- saturated low site (68137 0 24.51 00 N, 149135 0 46.26 00 W),  50 m apart at Toolik, Alaska. Several small samples from each site were combined ( 1 L total volume from each site) into a sealed plastic bag (one for each site), placed in an insulated container with an ice pack and sent by overnight air express to the Lamont- Doherty biology laboratories. To prevent possible excessive tem- perature shock, the samples were placed in a refrigerator (5 1C) for 24 h and then allowed to gradually come to 16 1C( summer minimum temperatures at the sampling site) in a temperature- controlled dark incubator for 3 d before analysis. All visible root segments (few and mainly in the high tussock sample) were re- moved and the soil was examined to eliminate insects or other invertebrates to ensure that the biota were largely microbes, or microbial arthropods at most. Light microscopic observations of Lugol’s preserved samples showed minimal presence of arthro- pods. Respiration of each soil sample was measured three times successively (to estimate method error) at 15 1C and 25 1C using an infrared gas analyzer with an opaque c. 300-cm 3 static chamber (Vernier, Beaverton, OR), equipped with a constant temperature bath (VWR International, Bridgeport, NJ). A subsample of each soil was replaced in the refrigerator for 6 d and rewarmed to 16 1C for 24 h before a second respiration analysis (1 wk later) to deter- mine possible effects of refrigerated temperature storage and lab- oratory manipulation on the respiratory analyses. Bacteria and heterotrophic nanoflagellates (HNAN) in aqueous soil suspension from each sample were enumerated by fluores- cence microscopy according to the method of Anderson et al. (2001) as adapted from Hobbie, Daley, and Jasper (1977) and re- ported as number per cm 3 of soil based on the sample used to prepare the soil suspension. Data were calculated in units of vol- ume (cm 3 ) as is appropriate for environmental and biogeographic applications. The pH of the soil suspension was assessed using an Accumet s Model 15 pH meter (Fisher Scientific, Pittsburgh, PA). Moisture content was assayed by change in weight after drying at 106 1C overnight. Organic content of the dried soil sample was obtained by change in weight after oxidation overnight at 375 1C in a high temperature oven. A Lugol’s iodine preserved subsample of the soil suspension was used to count testate amoebae (exclu- sive of empty tests) by exhaustively scanning all 20-ml aliquots from a 1-ml representative sample using a Nikon Diaphot s in- verted microscope (Melville, NY). The data were transformed as counts per ml and finally expressed as counts per cm 3 of original soil used to make the aqueous suspension. An aliquot of the freshly prepared soil suspension was used to enumerate naked amoebae according to the culture observation method routinely used in our laboratory and elsewhere (e.g. Anderson 2006). All microscopic examinations of the naked amoebae were made with a Nikon Diaphot s phase contrast inverted compound microscope (40X objective). RESULTS AND DISCUSSION The soil from the high, less water-saturated site, had a lower pH, lower moisture content, and higher organic content than soil from the low tussock site (Table 1). The respiratory activity and Q 10 coefficients were higher for the sample from the high site. The respiratory rates at 15 1C and 25 1C were, respectively, 2.2 and 2.7  those at the lower site. The Q 10 for the high site (2.4) was 1.3  that of the low site (1.7). The high site Q 10 is equivalent to the median global Q 10 5 2.4 (Raich and Schlesinger 1992) and similar to a Q 10 (2.6) reported for wet sedge tundra at Barrow, Alaska during the growing season (Mano et al. 2003). The lower pH at the high site may be due in part to the acidifying effects of higher respiratory CO 2 production. The substrate at the high site was largely undegraded moist moss and sphagnum; while at the low site, the substrate was finely fibrous, darker in color, and sat- urated with water. The respiration rates repeated after 1 wk, though somewhat lower for these smaller volume samples that had been re-refrigerated, were relatively similar in their propor- tions: the high site was 2.6  and 3.2  that of the low site for 15 1C and 25 1C assays, respectively; and the Q 10 coefficient for the high site was 1.2  that of the low site. Thus, it appears that laboratory manipulation of the samples, and restorage nearer to Corresponding Author: O. R. Anderson, Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York 10964— Telephone number: 11 845 365 8452; FAX number: 11 845 365 8150; e-mail: ora@ldeo.columbia.edu 218 J. Eukaryot. Microbiol., 57(2), 2010 pp. 218–219 r 2010 The Author(s) Journal compilation r 2010 by the International Society of Protistologists DOI: 10.1111/j.1550-7408.2009.00461.x Published by the International Society of Protistologists Eukaryotic Microbiology The Journal of