Host Plant Effects on Soil Microbial Assemblages in Ultramafic Soils in New Caledonia: Insights From the Ni-Hyperaccumulator Pycnandra acuminata and Its Non-Hyperaccumulator Congener P. fastuosa

Abstract

Recent advances have highlighted the importance of soil microorganisms in the ecology of metal hyperaccumulators, yet the associated microbial communities of the iconic nickel-hyperaccumulating tree, Pycnandra acuminata, remain unexplored. Here, we used environmental DNA to characterise and compare the soil bacterial and fungal communities beneath P. acuminata and a sympatric non-accumulating congener, Pycnandra fastuosa, in an ultramafic tropical forest. By assessing diversity indices, we revealed distinct bacterial richness patterns associated with host species and soil horizons. Both bacterial and fungal communities were structured by host plant identity, but only fungal communities showed an additional effect of soil depth. Several microbial taxa—including Chaetothyriales, Dothideomycetes, Hyaloscyphaceae (fungi), and Myxococcota, PLTA13 (Proteobacteria), Candidatus Udaeobacter, Chthoniobacter, and Bradyrhizobium (bacteria) displayed strong associations with P. acuminata, many of which are known to tolerate or thrive in metal-rich environments. While the mechanisms linking hyperaccumulator trees and their microbial partners remained difficult to disentangle, our findings provide a foundation for future research into plant–microbe–metal interactions and may inform innovative approaches for sustainable mining and ecosystem management in metal-rich regions that host natives (hyper)accumulator species.