Interaction between fungi and bacteria in soil
Fungi and bacteria comprise more than 90% of the soil microbial biomass and are the main agents for decomposition of organic matter in soil. Until recently it was thought that these two organism groups could be lumped in this respect and often total microbial biomass or total activity (respiration) are the only variables included in soil microbiology studies of decomposition and soil organic matter turn-over. However, there is increasing evidence that if decomposition is performed by bacteria or fungi, and thus energy is channelled through the bacterial or fungal food web, this can have profound effects on the ecosystem. Such effects can be direct, including effects on higher trophic levels in the food web, but also indirect, including effects on nutrient mineralization rates and nutrient transfer in soil, and even decisively influence the rate of carbon sequestration in the soil.
We have devised methods that specifically measure bacterial (using thymidine or leucine incorporation) or fungal (acetate incorporation into ergosterol) growth in soil. We also use phospholipid fatty acids (PLFA) as a way of detecting shifts in the microbial community, where the addition of 13C-labelled substrate can be used to trace decomposition through different microbial groups. We apply these techniques to study how different environmental variables affect the balance of fungal and bacterial decomposition in soil, e.g. effects of pH, different substrates, freezing/thawing, drying/rewetting, limiting factors. We are especially interested in possible interaction between these decomposer groups, including antagonism, competition and facilitation.