Pinus radiata seedlings rhizobiome shifts in response to foliar and root phosphite application

Soil health is an emerging concern in agriculture and is dependent on the microbial communities in the rhizosphere (rhizobiome). Phosphite-based products are used as bio-stimulants and/or fungicides. However, there is a lack of studies evaluating the impact of these products in nurseries, especially at the level of the rhizobiome. This work aims to assess the impact of phosphite (Phi) application on the rhizobiome of Pinus radiata seedlings. Two application modes (foliar and irrigation) were compared in an experimental setup with control treatments. Gas exchange parameters were evaluated to assess plant physiological performance. Bacterial rhizobiome analysis was performed using next generation sequencing targeting the 16S rRNA gene. Results showed that Phi application did not significantly affect plant photosynthetic performance. However, Phi irrigation led to a significant decrease in rhizobiome richness and diversity compared to control. Beta diversity analysis confirmed distinct microbial communities in the irrigated group. At the genus level, several acidophilic taxa, including Burkholderia and Aciditerrimonas, were significantly enriched in phosphite-irrigated samples, while others like Mucilaginibacter were reduced. The study reveals that Phi application, especially through irrigation, alters the structure of the rhizobiome in pine seedlings, leading to a decrease in richness and bacterial diversity. These findings highlight the importance of understanding the effects of commercial products, such as phosphite. This understanding is crucial to ensure sustainable plant growth and maintain soil health.