306 



P. W. Flanagan and F, L. Bunnell 



Oxygen Saturation, % 



40 



1 — rr 



28 Jun 



60 



Respiration, yxl (gdw soil) tir 

 30 Jul 



20 



40 



60 



25 Aug 



FIGURE 9-6. Depth profiles of soil respiration and oxygen saturation on 

 three days in wet meadows. Oxygen saturation measured by Polaro- 

 graphic analyses; respiration measured by Gilson respirometry. (Based 

 on data from Benoit and Gersper, unpubl.) 



Oxygen concentrations are influenced by root metabolism and the 

 associated rhizosphere effect as well as by soil moisture and respiration 

 by decomposers. Because of the intense respiratory activity of the roots 

 and the associated bacteria, the rhizosphere has a high demand for oxy- 

 gen. Since tundra plants typically have high root-to-shoot ratios there is 

 high demand for oxygen throughout the active layer. 



Microaerobic or anaerobic conditions depress the overall activity 

 and ehminate some functions of the soil microflora. Over short periods 

 anaerobic conditions reduce the rate of decomposition because of the 

 buildup of end-products which inhibit microbial activity. In the long 

 term, anaerobic conditions may be the major reason organic matter can 

 accumulate. All natural products except aromatic compounds can be de- 

 composed under anaerobic and aerobic conditions. The aromatic com- 

 pounds generally cannot be utilized as microbial substrates under anaer- 

 obic conditions. Furthermore, the decomposition of large molecular 

 weight compounds is largely the province of the fungi. Therefore, ligni- 

 colous and phenolic polymer compounds will be decomposed primarily 

 in the surface soil where oxygen values are higher and the fungal biomass 

 is greatest (Chapter 8). When phenolic compounds reach the lower levels 

 of the soil profile, either by leaching or transfer by microfauna, they 

 enter a zone of changed abiotic conditions where oxygen levels and tem- 



