Microflora Activities and Decomposition 293 



et al. 1977a, b). Field measures of decomposition and decomposition- 

 related phenomena are primarily measures of rates of loss of specific 

 substrate components. Four field measures have been employed. 



Weight losses from litter bags measure the rate at which litter be- 

 comes sufficiently disintegrated that it disappears from the litter bag. A 

 portion of this loss is due to microbial activity but some weight is lost by 

 leaching and physical comminution by invertebrates and by the freeze- 

 thaw cycle. Ingress of microbial, plant, animal and mineral matter can 

 confound estimates of weight loss. 



Chemical analyses of substrate composition coupled with measured 

 weight loss estimate the rate of disappearance of major chemical com- 

 pounds such as cellulose or phosphorus. These measures are also an inac- 

 curate estimate of microbial activity. Not only are other processes also 

 acting (e.g. leaching) but the microbial populations and their chemical 

 composition are inseparable from the substrates. 



Measurements of rates of evolution of carbon dioxide represent the 

 rate of mineralization of complex organic compounds to carbon dioxide, 

 water and residual constituents such as minerals, and are perhaps the 

 best measure of aerobic microbial activity. Depending on the substrate 

 measured and the method used, various inaccuracies are introduced, 

 either by the effects of methodology, as with the physical disturbance in 

 Gilson respirometry, or by inclusion of carbon dioxide evolved from 

 plant roots and soil invertebrates. Anaerobic decomposition processes 

 are incompletely measured by carbon dioxide evolution and may present 

 an important omission in some habitats. 



Measurements of microbial biomass during decomposition of 

 above- and belowground substrates permit one to relate the abundance 

 of major decomposer agents to substrate availability and quality. These 

 measures, coupled with laboratory data on microbial growth and yield 

 from varying substrates and information indicating microbial mainten- 

 ance demands, allow approximation of the microbial production in the 

 field. Microbial biomass and production may then be compared with 

 similar measures from leaves, roots, microfauna etc. Additionally, stud- 

 ies of microbial biomass permit compensation for underestimates of 

 weight loss caused by growth of microbial tissue in litter bags. By know- 

 ing microbial mineral content per gram we can approximate values for 

 mineral immobilization and cycling in microbial biomass and produc- 

 tion, respectively. 



In the subsequent discussion, both field and laboratory measures are 

 employed to help define patterns of decomposition. Since decomposition 

 is equated with the microbial mineralization of carbon, these measures 

 are to varying degrees inaccurate. No one measure discretely encom- 

 passes decomposition as defined, but integrated with a knowledge of mi- 

 crobial biomass, dynamics, and physiology the measures contribute to a 



