Role of Soil Fauna in Nitrogen Cycling and Plant Succession: Plant functional identity has consistent effects on nematode communities across successional stages

Soil fauna communities are known to change during succession as the soil age and vegetation develops. Moreover, plant functional identity (henceforth PFI) influence belowground assemblages within successional stages. Given changes in environmental conditions the influence of PFI is likely to differ across stages; however, the relative contribution of functional identity across successional stages remains unknown. We sampled nematode communities associated with nitrogen (N) fixing and non-fixing plants across a well-described chronosequence (Cooloola, QLD, Australia) to assess the relative importance of functional plant identity and successional stage on nematode community composition. Nematode densities were influenced by successional stage, displaying unimodal relationships associated with similar patterns in aboveground biomass and soil C and N contents. Densities peaked at the late progressive stage, where colonizer bacterivores were particularly abundant near N-fixing plants, followed by a decrease in nematode numbers and a shift towards k-strategists in the later successional stages. A PERMANOVA indicated that successional stage (39%) and PFI (20%) accounted for more than half of the observed variation in assemblage composition. This support our hypothesis that nematode assemblages change during succession, but that plant functional identity play a key role in structuring nematode communities within successional stages. However, contrary to our expectations, there was no interaction between the two factors, indicating that plant functional identity consistently influences soil nematode assemblages across successional stages. Our results confirm that plant functional identity is an important contributor to soil fauna assemblages across primary succession.