SOIL BIOTA AND GLOBAL CHANGE AT THE ECOSYSTEM-LEVEL - DESCRIBING SOILBIOTA IN MATHEMATICAL-MODELS

All current mathematical models of the soil system are underpinned by a wealth of research into soil biology and new research continues to i mprove the description of the real world by mathematical models. In th is review we examine the various approaches for describing soil biolog y in mathematical models and discuss the use of each type of model in global change research. The approaches represented among models partic ipating in the Global Change and Terrestrial Ecosystems (GCTE) Soil Or ganic Matter Network (SOMNET) are described. We examine the relative a dvantages and constraints of each modelling approach and, using these, suggest appropriate uses of each. We show that for predictive purpose s at ecosystem scale and higher, process-orientated models (which have only an implicit description of soil organisms) are most commonly use d. As a research tool at the ecosystem level, both process-orientated and organism-orientated models (in which functional or taxonomic group s of soil organisms are explicitly described) are commonly used. Becau se of uncertainties introduced in internal model parameter estimation and system feedbacks, the predictive use of organism-orientated models at the ecosystem scale and larger is currently less feasible than is the use of process-orientated models. In some specific circumstances, however, an explicit description of some functional groups of soil org anisms within models may be required to adequately describe the effect s of global change. No existing models can adequately predict the feed back between global change, a change in soil community function, and t he response of the changed system to future global change. To find out if these feedbacks exist and to what extent they affect future global change, more research is urgently required into the response of soil community function to global change and its potential ecosystem-level effects.