Microflora Activities and Decomposition 315 

 1 ' ^ 



FIGURE 9-9. Seasonal 

 courses of the evolution of 

 carbon dioxide from soils 

 of four microtopographic 

 units and soil temperature 

 near the surface in the ba- 

 sin of a low-centered poly- 

 gon. Carbon flux meas- 

 ured by KOH titrations in 

 darkened lysimeters. Data 

 are ten-day running means 

 for 1973. (Benoit, unpubi) 



ture level is about 75 to 80%. Few measures incorporating higher mois- 

 ture levels were available and the estimate is likely low. Rates of soil res- 

 piration as measured by Gilson respirometry can be extrapolated only 

 tenuously to estimate decomposition rates in the field. At best they repre- 

 sent a potential rate of decomposition that may not be realized. 



Another estimate of field decomposition rate and the factors which 

 control it can be made from in situ measurements of carbon dioxide evo- 

 lution although these measures include respiration of roots as well as 

 microflora. Field data were obtained by daily potassium hydroxide titra- 

 tion of gas collected from plastic cores sunk into the soil in 1973. Mea- 

 sures of carbon dioxide evolution from different microtopographic units 

 all peak in early August (Figure 9-9). Although the peak appears correl- 

 ated with temperature, early August is also the time of maximum above- 

 ground biomass of vascular plants and intense activity by soil fauna. 

 Logarithmic regression of the daily evolution of CO2 m"% as measured 

 by lysimeters in wet meadow soils, against mean daily soil temperature 

 estimates a Qio of 1.89: 



R = 1465.6x1.89 



Tmean/lO 



r' = 0.37, a < 0.01 



where R is ml CO2 m ^ day ' and Tmean is the mean daily temperature. 



