Soil biodiversity and nutrient cycling in a chronosequence of abandoned agricultural fields

Land abandonment is considered an effective tool for restoring biodiversity and ecosystem functions. Thus far little attention is given to the role of soil biodiversity. Here, we present results of a soil biodiversity and ecosystem functioning study from a chonosequence of ex-arable fields in The Netherlands (Veluwe LTO). These fields are typically managed by low-intensive grazing while undergoing a transition from an arable system into species-rich grassland. We present a method to investigate the soil biodiversity in the Veluwe chronosequence from the EcoFINDERS field sampling campaign in 2011. Abandoning agricultural fields triggers a change in the species composition and possibly the way species interact. We were able to reconstruct the full soil food web (from microorganisms to earthworms) at 10 fields that were taken out of production at different points in history. In total ~18000 species were found. The co-occurrence of species at different locations was compared by several network presentations. We also present the results of a mesocosm experiment where we have employed 13-C-CO2 pulse labeling and 15-N labeling to assess the short term fate, turnover and retention of recent plant-assimilated carbon and nitrogen in cores with field soil. Samples have been collected of aboveground and belowground plant tissues, soil bacterial and fungal PLFA biomarkers, nematodes, enchytraeids, mites, collembola, earthworms, and other soil fauna. Our aim was to investigate how the carbon and nitrogen is sequestered in the different components of the soil food web in relation to time since abandonment. We used the data from these cores on biomass and carbon-nitrogen contents of the feeding guilds within the soil food web to run an existing carbon/nitrogen flow model for grasslands. We discuss these results in relation to the soil biodiversity network analyses in order to predict the change in ecosystem processes during land abandonment and secondary succession.