BIODIVERSITY AND ECOSYSTEM FUNCTIONING IN SOIL

We review the current knowledge on biodiversity in soils, its role in ecosystem processes, its importance for human purposes, and its resili ence against stress and disturbance. The number of existing species is vastly higher than the number described, even in the macroscopically visible taxa, and biogeographical syntheses are largely lacking. A maj or effort in taxonomy and the training of a new generation of systemat ists is imperative. This effort has to be focussed on the groups of so il organisms that, to the best of our knowledge, play key roles in eco system functioning. To identify such groups, spheres of influence (SOI ) of soil biota - such as the root biota, the shredders of organic mat ter and the soil bioturbators - are recognized that presumably control ecosystem processes, for example, through interactions with plants. W ithin those SOI, functional groups of soil organisms are recognized. R esearch questions of the highest urgency are the assignment of species to functional groups and determining the redundancy of species within functional groups. These priorities follow from the need to address t he extent of any loss of functioning in soils, associated with intensi ve agriculture, forest disturbance, pollution of the environment, and global environmental change. The soil biota considered at present to b e most at risk are species-poor functional groups among macrofaunal sh redders of organic matter, bioturbators of soil, specialized bacteria like nitrifiers and nitrogen fixers, and fungiforming mycorrhizas. An experimental approach in addressing these research priorities is neede d, using longterm and large-scale field experiments and modern methods of geostatistics and geographic information systems.