Native Arbuscular Mycorrhizal Fungi Improved Araucaria araucana Growth over Commercial Inoculum Under Greenhouse and Field Conditions

Araucaria araucana forests in the Coastal Mountain range of Chile are highly endangered due to their population isolation, wildfires, and land-use change. Mycorrhizas constitute a potential restoration tool for this species. Firstly, in a greenhouse we tested A. araucana growth responses to single/mixed commercial and native arbuscular mycorrhizal fungi (AMF) inoculum. Secondly, in plantations under contrasting tree covers we compared the growth responses of greenhouse-grown A. araucana seedlings with and without native AMF inoculum. Four treatments were established under greenhouse conditions (25 A. araucana seedlings per treatment): T0, non-mycorrhizal control; T1, single AMF species commercial inoculum; T2, four AMF species commercial inoculum; and T3, 17 AMF species native inoculum. Seedlings were grown for 1.5 years, after which, seven growth traits and the Ritchie plant quality index were recorded. After this, in Nahuelbuta National Park (native inoculum and seeds’ site), a total of 80 seedlings were sown for 13 months: 40 from T0 and 40 from T3, in two contrasting plots regarding their tree mycorrhizal dominance (ectomycorrhizal vs. arbuscular mycorrhizal). Under greenhouse conditions, native AMF inoculum, over one and four species’ commercial inoculum, increased A. araucana seedlings’ fresh and dry weight of shoots and roots. In situ, the sympatric combination of native seedlings and AMF inoculum growing under original soil conditions, resulted in higher plant growth and quality. Functional complementarity among AMF species probably explains our greenhouse results, as inoculum complexity is a good predictor of plant performance. Local adaptation of AMF and seedlings to soil biotic/abiotic conditions might explain our plantation results.