Soil nematodes modify interactions between nitrogen-fixing and non-fixing tree seedlings from late, but not early, successional stages

Aims: Plant community dynamics are influenced by interspecific interactions. Previous studies have shown that soil organisms play a key role in such interactions, but few studies have quantified soil fauna contributions.

Methods: We investigated the effects of root lesion (RLN) and bacterial feeding (BFN) nematodes on the interaction between seedlings of nitrogen-(N)-fixing tree species of Acacia and non-fixing Banksia from early and late successional stages of a temperate forest in a pot experiment.

Results: Nematodes had consistent, albeit minor, negative effects on both N-fixers and non-fixers in the early successional stage scenario. By contrast, BFNs increased biomass production of both species in late-stage monocultures and in Banksia in mixed cultures. Moreover, RLNs negatively affected late-stage Banksia in monocultures but promoted its biomass production when grown with Acacia. Reduced ¹⁵N concentration in Banksia indicates that the switch was driven by transfer of N from Acacia facilitated by RLN.

Conclusions: Soil nematodes thus moderate interspecific interactions differently in early and late successional stages.