Microflora Activities and Decomposition 331 



The question concerning root contribution to total soil respiration is 

 partially answered for Barrow tundra soils. Billings et al. (1977) esti- 

 mated total soil respiration ranging from 75 to 125 mg CO2 m"^ hr"' in 

 mid-June 1972. During the last week in July 1972, total soil respiration as 

 measured by Billings et al. (1977) ranged from 150 to 300 mg CO2 m"' 

 hr"'. The values of Billings et al. are similar to calculations based solely 

 on microbes, and are somewhat lower than actual field measurements 

 made on root-free soils at Barrow (Benoit, unpubl.). 



Flanagan and Veum (1974), using respiration data measured in situ 

 in Barrow tundra soils, calculated the average release of CO2 from these 

 soils to be in the range 147 to 235 mg CO2 m'^ hr"'. The calculated rates 

 do not include root respiration. They are about five times less than meas- 

 urements made on temperate forest floors (Witkamp 1966) and about 

 three times less than the average measurements made in tundra soils of 

 the Taimyr peninsula, USSR (Aristoskaya and Parinkina 1972), which 

 include root respiration. The comparison between the Soviet and U.S. 

 data above suggests that microbes may contribute around 30% of total 

 soil respiration. This speculation is in general agreement with rates of 

 respiration simulated by ABISKO 11 (Figure 9-12) which indicate that root 

 respiration may contribute from 33 to 70% of total soil respiration on 

 any given day (Bunnell and Scoullar 1975). This range is somewhat lower 

 than the 50 to 93% contribution by root respiration calculated by Billings 

 et al. (1978). 



In summary, the observed rates of microbial turnover in the most 

 productive areas very nearly account for the total input of organic mat- 

 ter. Estimated rates of decomposition below ground are compatible with 

 measures of soil respiration, and indicate that some microtopographic 

 units may not be accumulating organic matter. Estimates of carbon diox- 

 ide evolution by decomposition above and below ground range from 2.8 

 to 5.6 g CO2 m"^ day"' (Flanagan and Veum 1974), in general agreement 

 with estimates of carbon dioxide incorporation by atmospheric flux. 



Microorganisms and Mineral Nutrient Cycling 



The distribution of nitrogen and phosphorus in various ecosystem 

 components can be calculated using data on nutrient content of live 

 fungal tissues from Flanagan and Van Cleve (1977), and nitrogen and 

 phosphorus content of soils and decaying matter from Chapter 12 and 

 Flint and Gersper (1974). Flint and Gersper estimated that the wet mea- 

 dow tundra required 6.4 g N m"^ yr"' for plant and animal growth. Ac- 

 cording to the calculations above, gross release of nitrogen by decompo- 

 sition is about 7.5 g m"^ yr"', while the combination of exchangeable and 

 dissolved inorganic nitrogen amounts to 8.0 g m"^ (Figure 9-13). 



