360 



J. E. Hobbieetal. 



TABLE 8-8 Decomposition Coefficients, K, * and K2** from Various Studies 



*Ki = coefficient of loss of total leachable fraction (% yr 

 **K2 = coefficient of loss due to hydrolysis (% yr~ ). 



-1 



dominant in the initial stages of decomposition when soluble, low 

 molecular weight organic compounds are lost. Hydrolysis, the long-term 

 enzymatic breakdown of structural plant matter, dominates next. 

 Trituration, mechanical breakdown by animals or physical forces (water 

 movement, freeze-thaw), dominates the final stages of decomposition. 



The combination of leaching and hydrolysis can be represented as the 

 sum of two first-order equations of the form W(t)= lVe~'^' where W(t) is 

 the litter remaining at time /, W \s the litter originally present, and A^ is a 

 coefficient of decrease (Bunnell and Tail 1974). From this a Ki may be 

 calculated for leaching and a A' 2 for hydrolysis (in percent weight loss per 

 year of total substrate available to that process). These values are 

 approximations only and have been calculated on the basis of an entire 

 year so that they may be compared with other measurements (Table 8-8). 

 While the Ki rates are comparable with the other values, they only obtain 

 for a 3-month decomposition season.so presumably the loss would be 33% 

 per season in the arctic ponds. The K2 rates are noticeably lower in the 

 arctic leaf material but a comparison of tree leaves and sedge leaves may 

 not be valid. In fact, the data summarized by Saunders (1976) show that 

 the rate of decomposition is species-dependent and can range from 0.2 to 

 1.75% day ' for tree leaves. Perhaps the best analogy in Table 8-8 would 

 be between the yellow Carex leaves and leaf material reported by Hall 

 (1972), as both underwent the natural process of retranslocation before 

 being subject to decomposition. However, the low temperatures at which 

 the arctic decomposition took place may well be even more important than 

 the differences between types of plant material. 



The comparisons above are with decomposition rates of litter 

 incubated in water. Many studies of decomposition on land have shown 



