Reduced growth of Pinus radiata in the presence of the Australian native Allocasuarina nana via direct allelopathy and inhibition of the pine-supporting mycorrhizal community

The establishment and productivity of new forest plantations can be significantly impacted by the presence of native vegetation. In a study site in New South Wales, Australia, the growth of a Pinus radiata plantation has been virtually halted in areas dominated by the native shrub Allocasuarina nana, effects that persist for decades even after its physical removal. To determine the mechanism by which A. nana impedes P. radiata growth, we compared the fungal soil community and metabolomic profile of soils in patches rich in A. nana with adjacent healthy P. radiata patches and the transition zone between them. This data was complemented by a pot experiment to assess P. radiata growth in soils from the different vegetation areas with and without a viable soil community or the addition of A. nana roots or exudates. Together, the data demonstrates that these A. nana soils are likely inhibitory to P. radiata growth through a dual mechanism: impacting the growth of the pine directly through root associated metabolites and indirectly through the inhibition of the fungal community supporting P. radiata health, including ectomycorrhizal fungi.