Isolation and characterization of soil cyanobacteria and microalgae and evaluation of their potential as plant biostimulants

Background and Aims Biocrusts are found on soil surface resulting from an association between soil particles and microorganisms. Photoautotrophic cyanobacteria and microalgae are pioneers on biocrusts formation, promoting soil stability, nutrients availability and water retention, leading to the development of other communities. This work aimed at isolating and characterizing cyanobacteria/microalgae from biocrusts (Central Portugal) and to assess their potential as plant biostimulants, as well as obtaining an insight into their mechanism(s) of action. Methods Microorganisms were isolated through successive spread plating/serial dilutions and characterized using genetical analysis/morphological traits. An initial screening was performed using exudates from each microorganism and two plant species, Arabidopsis thaliana and Lolium multiflorum . Subsequently, the selected microorganisms were tested as a consortium in hydroponic systems. Biometric and biochemical parameters were evaluated for both plant species. Results The consortium microorganisms belong to genera often found in soils/biocrusts: Trichocoleus, Nodosilinea, Microcoleus (filamentous cyanobacteria), Nostoc (diazotrophic heterocystous cyanobacteria), and Klebsormidium (filamentous microalga), and some of them have the capacity to produce phytohormones and/or siderophores. The consortium showed biostimulant potential in hydroponic cultures, promoting plant growth and enhancing physiological productivity related parameters. Stress related parameters revealed that the microorganisms did not lead to a stressful situation. However, a significant increase in proline was observed, endorsing a role of this molecule in this process. Conclusion This study contributes to the knowledge on the biodiversity of cyanobacteria and microalgae from Portuguese soils and highlights their potential as biostimulants, constituting a step forward towards understanding the molecular mechanisms behind this effect.