308 P. W. Flanagan and F. L. Bunnell 



operating separately from or in concert with a deficiency of oxygen 

 reduces microfloral metabolism (Burges 1958, Griffin 1972). 



The highest oxygen levels measured within the upper 20 cm of soil 

 were observed in the soils of the basins and rims of low-centered poly- 

 gons and the tops of high-centered polygons (Figure 7-6). It is surprising 

 to find that on the dates they were sampled the basins of low-centered 

 polygons had high oxygen values throughout the soil profile. Soil thin 

 sections from basins, unlike rims, indicate a structure that should impede 

 drainage and aeration (Everett, pers. comm.). The data for both in vitro 

 respirometry and measured evolution of carbon dioxide indicate that 

 basins of low-centered polygons have low rates of decomposer activity 

 (Figure 9-9). For example, in 1972 the mean seasonal rate of respiration, 

 as measured by Gilson respirometry, for 0- to 2-cm basin soils was 10.06 

 lA O2 (gdw soil)"' hr"' whereas the values from similar depths in the 

 trough and very wet meadow were 31.37 and 43.15 m1 O2 (gdw soil)"' hr"' 

 respectively. The consistently low decomposer activity and low primary 

 productivity probably act to maintain relatively high levels of oxygen in 

 the basin soils. 



The shift of bacteria-to-fungi ratios along the oxygen gradient 

 (Chapter 8) suggests that anaerobiosis does not eliminate decomposition 

 of the soil organic matter but changes the quality of that decomposition. 

 In the wet meadow, depressed oxygen concentrations in the deeper soils 

 were associated with high levels of decomposer activity measured by Gil- 

 son respirometry (Figure 9-6). Thus the high values for respiration from 

 subsurface samples represent activity of facultative bacteria after full in- 

 duction of potential for oxidative phosphorylation in the Gilson respir- 

 ometer. The rapid response to oxygen indicates the active enzymatic state 

 of the cells. The zone of anaerobiosis at the front of the thaw zone ap- 

 pears to be a result of the rapid decomposition of readily available 

 substrates. 



Experiments with heated soil further demonstrate that anaerobic 

 conditions per se do not prevent decomposer activity in tundra soils. 

 Oxygen saturation in the soil solution in heated soils declined to 0% by 

 the 3-cm depth. On these plots methane routinely composed 60% (with a 

 range of 42 to 65% of the gas released), with the balance primarily of 

 carbon dioxide. Methane production provides good evidence for anaero- 

 bic activity because methane producers represent one of the most strictly 

 anaerobic groups, and can be killed easily by transitory exposure to oxy- 

 gen. Despite anaerobic conditions, rates of decomposition were high in 

 heated soils. Evolution of carbon dioxide over a 33-day period in late 

 summer was 39% higher in heated soils, and after 12 months the energy 

 content in the heated soil was less than in control soils by 21 % in the up- 

 per 2 cm and by 16% at depths of 7 to 12 cm. The higher rates of micro- 

 bial respiration in the heated soils are a result of the increased tempera- 



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