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

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.

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.

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.

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