Ecological roles of soil microalgae and cyanobacteria in a Mediterranean olive orchard under differentiated management practices

Soil microalgae and cyanobacteria (SM&C) play a crucial role in sustainable agricultural practices due to their diverse ecological functions. These microorganisms are actively involved in biogeochemical cycling, enhance soil biomass, contribute essential nutrients for plant development, and create favorable microenvironments by releasing bioactive compounds. They also establish synergistic relationships with other soil microbes. This study aimed to investigate the composition and functional potential of SM&C communities in a Mediterranean olive orchard located in a semi-arid region (Ferrandina, Basilicata, Italy), managed for over 22 years under two different systems: sustainable (Smng) and conventional (Cmng). Microalgae and cyanobacteria were cultured using two selective liquid media—one with nitrogen to support general growth, and one nitrogen-free to isolate nitrogen-fixing cyanobacteria. Results showed that sustainably managed soils harbored significantly higher populations of microalgae (2.210 × 10⁴ g⁻¹ soil in Smng vs. 0.872 × 10⁴ g⁻¹ soil in Cmng) and cyanobacteria (0.408 × 10² g⁻¹ soil in Smng vs. 0.240 × 10² g⁻¹ soil in Cmng). Dominant taxa were identified through light microscopy and metagenomic analysis targeting 16S, 18S, and ITS rDNA regions. In Cmng, green algal genera such as Trebouxia, Euglena, and Chaetophora, along with the diatom Cymbella, were predominant. Conversely, in Smng, a higher prevalence of the cyanobacterial genus Anabaena, green algae Oedogonium and Scenedesmus, and the diatoms Navicula and Pinnularia was observed. Soil management also influenced the metabolic output of SM&C, with Smng soils showing upregulation of biosynthetic pathways associated with secondary metabolites, phytohormones, fatty acids, and lipids, which are known to enhance plant growth. Overall, the findings highlight the potential of SM&C not only for ecological functioning but also as valuable allies in maintaining soil health and improving crop productivity. This study was carried out within the Agritech National Research Center and received funding from the European Union Next-GenerationEU (PIANO NAZIONALE DI RIPRESA E RESILIENZA (PNRR) – MISSIONE 4 COMPONENTE 2, INVESTIMENTO 1.4 – D.D. 1032 17/06/2022, CN00000022). This manuscript reflects only the authors’ views and opinions, neither the European Union nor the European Commission can be considered responsible for them.