Decomposer invasion rate, decomposer growth rate, and substrate chemical quality: how they influence soil organic matter turnover

The physical structure of litter can be introduced into decomposition models in several ways. We have used the continuous-quality theory to analyse three models: (i) initial quality of litter or growth rate of decomposers depends on the physical structure of litter, (ii) decomposer colonization rate of litter depends on litter shape and size, and (iii) a constant decomposition rate, i.e., no effect of litter shape and size. Our analysis shows that it is important to separate the physical factors affecting access to carbon (C), i.e., decomposer colonization rate, from the chemical characteristics of litter in decomposition models. Soil C stores predicted with models based on the colonization rate of decomposers are much less sensitive to the shape and size of coarse woody litter than predictions based on the two other approaches. The effect of temperature on steady-state soil C storage is greater for litter that is colonized rapidly than for litter that is colonized slowly. The decomposition of litter types like needles, fine roots, and fieldlayer vegetation is therefore more sensitive to temperature changes than the decomposition of stems and coarse roots, and this difference is more pronounced at high temperatures than at low temperatures.