Abstract
Reduction of pesticide use and mitigation of nitrogen and other nutrient losses from soil are important policy objectives. There are strong indications that in terrestrial ecosystems the occurrence of plant diseases and the loss of nutrients are related to the diversity of vegetation. Soil-borne diseases are rare in natural ecosystems with a diverse vegetation and nutrient losses from such systems are usually small. In the proposed research programme we will address the general hypothesis that high biodiversity in terrestrial ecosystems confers high soil suppressive ness against diseases and high nutrient retention in soil. This follows from the working hypothesis that the coupling of activities between the plant and the decomposer subsystem, i.e. the heterotrophic soil community, is a key feature in terrestrial ecosystem functioning. Permanent grassland and agricultural fields, derived from the same grassland 20 years ago, will be compared in terms of above- and below-ground biodiversity, production and chemical composition of plant biomass and litter, in relation to soil suppressive ness and nutrient fluxes. Part of the grassland will be turned into agriculture. In addition to the current agricultural practice, treatments are foreseen that differ in above-ground biodiversity, in particular biodiversity of functional groups of plants. These treatments will allow to establish relationships between biodiversity and soil suppressive ness and nutrient retention and the changes therein, following simplification or diversification of the ecosystem. The degree of soil suppressive ness will be experimentally tested by bio-assays, testing the infection of pathogen-sensitive test plants and the potential of soils to reduce the development of plant pathogen populations. Nitrogen turnover in the food web in the soil-plant system will be measured and simulated in order to evaluate the supposed mechanism of nutrient retention and to evaluate the possible effects of biodiversity beyond the range investigated in the field. Existing food web models will be elaborated to include effects of the plant and those of non-trophic relationships and a wider range of functional groups of biota than hitherto reported. Microcosm experiments will parallel field studies to answer specific questions. Confirmation of the possible relationship between biodiversity and soil suppressive ness and nutrient retention will allow the design of agricultural systems that are both biologically more diverse and less pollutant.
Netherlands