Soil food web structure and mineralization during ecosystem development after land abandonment

1. Restoration of natural species-rich heathlands on abandoned agricultural land is a common land use change in North-West Europe. However, it takes several decades to restore heathland vegetation. To speed up the restoration process, first changes in soil processes, e.g. mineralisation, and in soil food web structure after abandonment need to be understood. Current theory predicts that after abandonment biomass and contribution to mineralisation of organisms at higher trophic levels increases and that there will be a shift from a bacteria to a fungi dominated soil food web.
2. We measured C and N mineralisation rates and analysed the soil food web structure in three ex-arable fields and used a food web model to calculate contributions of soil organisms to mineralisation. The soil food web structure and contribution to mineralisation were analysed in terms of trophic levels and energy channels.
3. Biomasses and contributions to mineralisation at higher trophic levels unexpectedly decreased during restoration. Fungal channel biomass increased as hypothesized, but bacterial channel biomass also increased during transition. However, while the fungal channel contributions to mineralisation increased, the bacterial channel contributions decreased.
4. The decreases in contributions to mineralisation suggest that groups at high trophic levels became less important for soil processes during restoration. Shifts from a bacterial to a fungal channel biomass dominated food web were not found. However, fungal channel contributions to mineralisation increased during restoration, while that of the bacterial channel did not so that soil processes became more dependent on organisms in the fungal channel.