Biostimulatory Effects of Limnospira indica PCC 8005 on the Modulation of Rhizosphere and Endosphere Microbiota and its Impact on Plant Growth

The increasing demand for sustainable agriculture has highlighted the need for innovative strategies to enhance crop productivity while reducing environmental impact. This study evaluates the potential of Limnospira indica-based biostimulants to promote plant growth in Solanum lycopersicum (tomato) and modulate rhizosphere and endospheric microbiota. Two culture derived fraction of L. indica –culture media (CM) and biomass extracts (BM)– were prepared from nitrate-sufficient (N+) and nitrate-deficient (N-) cultures and applied through amendment or foliar treatments. Phenotypic analyses revealed that biostimulant extracts produced from L. indica CM N- significantly enhanced flower and fruit production, as well as microbial diversity compared to water controls and N+ treatments. 16S sequencing analyses demonstrated that biostimulant extracts enriched plant growth-promoting genera known for their roles in nitrogen fixation, phytohormone production, stress resilience and bioremediation. While numerous metabolites impacting plants are known, polysaccharides excreted under nitrate-deficient conditions were suggested as key drivers of microbial dynamics, promoting biofilm formation and enhancing plant-microbe interactions. Temporal analyses highlighted shifts in microbial communities further correlated with phenotypic improvements. These findings underscore the potential of nitrate-deficient L. indica-based biostimulant extracts to sustainably optimise plant growth by targeting specific microbiota interactions. This study provides a foundation for advancing biostimulant formulations and promoting environmentally friendly agricultural practices.