To determine the effects of metal contamination as a result of long-term sewage sludge application on the diversity and selected functions of the entire soil microbial community as well as the diversity of specific microbial groups and to relate the observed effects to concentrations of the bioavailable fraction of heavy metals in the soils.
The relationship between microbial function and diversity in soils is poorly characterised. The main hypothesis of this project is that as a result of heavy metal stress, microbial diversity will be reduced before there is a loss of function. This hypothesis will be tested by examining microbial diversity in metal contaminated soils which previous studies have shown to have suffered a loss of function to differing degrees. Metal toxicity effects will be related to metal-ion-species concentration in the soil solution, rather than total or 'extractable' soil metal concentrations which overcomes previous problems caused by differences in metal availability between soils at similar total metal concentrations.
A variety of physiological and molecular biology techniques will be used to study long-term effects of heavy metal pollution on the biodiversity of microorganisms in soils. It is hoped that the studies on microbial diversity will allow the development of 'early warning' systems which can be used to indicate deleterious effects of pollutants before catastrophic loss of functionality or of some whole groups of organisms has occurred. Heavy metal chemistry is complex and differences in toxicity of heavy metals between different soils are often difficult to explain. Advances in methods to determine the ionic speciation of metals allow the measurement of the free-ion-species in contaminated soils which constitute the toxic 'bioavailable' metal fraction or microorganisms which are bathed in the soil solution. In this research the ionic speciation of heavy metals will be measured in all the soils for which the microbial diversity is studied, thus allowing a biologically meaningful interpretation of the problems of long-term heavy metal contamination.
Participants will examine the biodiversity of the microbial communities in heavy-metal polluted soils, each examining different methods of looking at microbial diversity, or looking at the diversity of a particular group of microorganisms within the microbial biomass. All participants will conduct their research on the same soils from long-term field experiments which have been treated with heavy metal contaminated sewage sludge in replicated field experiments over a long time period and which also contain replicated control plots. A number of other, more recently established field experiments and polluted sites will also be sampled to examine the effects of heavy metals on soil microbial communities as the metal contamination gradually increases.
Within the project the different participants will assess in the same metal-contaminated soils:
- the diversity of rhizobia.
- The diversity of arbuscular mycorrhizal fungi (AMF).
- The physiological characteristics of the soil community in relation to its diversity determined by physiological and molecular biology techniques.
- The diversity of microbial communities determined by DNA analysis.
- The bioavailability of heavy metals in the soils.
This will allow the development of comparative data of the effects of heavy metals on diversity and function of soil microorganisms at different scales of resolution.
Funding SchemeCSC - Cost-sharing contracts
AL5 2JQ Harpenden, Herts
750 07 Uppsala