Rhizosphere bacterial and fungal communities of Araucaria angustifolia in natural forests and plantations: Insights for sustainable management

Abstract

The Araucaria Forests of South America are critically endangered due to historical deforestation and overexploitation. Remaining fragments are now confined to southern Brazil and northeastern Argentina (Misiones). Establishing A. angustifolia plantations for wood production could play a crucial role in the conservation of this species by expanding its distribution area. However, restrictions on the regeneration and development of A. angustifolia in these managed systems can be hindered by soil degradation. Since the microbial community living in the roots is essential for plant health, understanding its composition across different land use scenarios is key to improving conservation efforts. The aim of this study was to characterize the bacterial and fungal communities in the rhizosphere of A. angustifolia comparing natural forests and plantations with distinct management histories in order to assess the contribution of plantations to sustaining this microbiome in the medium and long term. Using a metabarcoding approach targeting ribosomal markers, we analyzed the bacterial and fungal rhizosphere communities and correlated them with stand structure and soil physico-chemical properties. The studied plantations exhibited lower nitrogen, organic matter, carbon, and soil water content, as well as higher pH and soil bulk density compared to natural forests. While the alpha diversity of rhizosphere bacteria and fungi did not differ significantly between habitats, we found clear differences in community composition. Key stand structure attributes (e.g., understory cover and tree richness) and soil variables (e.g., pH, water content, organic matter, and bulk density), were the most influential factors shaping the microbial assemblages. For instance, the decline of bacterial genera such as Candidatus Koribacter, Acidibacter, and Acidothermus in plantations was associated with higher pH levels. Furthermore, plantations showed reduced abundances of key beneficial fungi for plant growth and biocontrol, such as Trichoderma and Aspergillus, and a higher abundance of genera adapted to restrictive environments, such as Brevibacillus and Anoxybacillus. In contrast, second-rotation plantations had a higher abundance of arbuscular mycorrhizal fungi. These findings underscore the importance of management strategies focused on minimizing nutrient losses, promoting mycorrhizal fungi, and supporting soil health to ensure the long-term resilience and productivity of Araucaria plantations.