SOIL FOOD WEBS AND ECOSYSTEM PROCESSES - DECOMPOSITION IN DONOR-CONTROL AND LOTKA-VOLTERRA SYSTEMS

We analyze how populations and food web structure affect the decomposi tion process. Based on a theory of carbon dynamics at the ecosystem le vel and food web theory at the population level, a link between popula tion- and ecosystem-level theories is generated through a series of fa ctors connecting population parameters to ecosystem-level decompositio n rates. These factors are the ratio of the steady state biomass of a functional group to the mass of its resource, the total mortality rate of a functional group, and a carbon recycling index defined for each living component in the decomposer system. The factors defined at the primary decemposer level embody information about the whole food web. Two different assumptions about the mechanisms of trophic interactions in the food web are used: donor-control and Lotka-Volterra. The resul ts show how the structure of the soil community and the characteristic s and properties of soil fauna contribute to the decomposition process . Under the assumption of donor-controlled trophic interactions, the a ddition of soil fauna will always increase decomposition rate (mass lo ss), and the decomposition rate increases with the number of trophic l evels. However, the maximum increase in decomposition rate due to faun a is determined by microbial properties only. These results do not hol d under the assumption of Lotka-Volterra trophic interactions, where t he decomposition rate depends on whether the number of trophic levels is odd or even, interaction structure, and the input of detritus to th e system.