Global change effects on a mechanistic decomposer food web model

Kuijper, L. D., Berg, M. P., Morriën, E., Kooi, B. W. and Verhoef, H. A. 2005. Global change effects on a mechanistic decomposer food web model. Global Change Biology 11: 249 - 265


Global change may affect the structure and functioning of decomposer food webs through qualitative changes in freshly fallen litter. We analyzed the predicted effects of a changing environment on a dynamic model of a donor-controlled natural decomposer ecosystem near Wekerom, The Netherlands. This system consists of fungi, bacteria, fungivores, bacterivores and omnivores feeding on microbiota and litter as well. The model concentrates on carbon and nitrogen flows through the trophic niches that define this decomposer system, and is designed to predict litter masses and abundances of soil biota. For modeling purposes, the quality of freshly fallen leaf litter is defined in terms of nitrogenous and non-nitrogenous components, of which refractory and labile forms are present. The environmental impacts of elevated CO2, enhanced UV-B and eutrophication, each with their own influence on leaf litter quality, are studied. The model predicts steady-state dynamics exclusively, for all three scenario's. Environmental changes impact most demonstratively on the highest trophic niches, and affect microbiotic abundances and litter decomposition rates to a lesser extent. We conclude that the absence of trophic cascade effects and non-equilibrium dynamics may be attributed to weak trophic links occurring in the system. We set out a number of experimentally testable hypotheses that may improve understanding of ecosystem dynamics.

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