Background: Meeting rising food demand with sustainable strategies
Global food demand is climbing as the world population grows toward 9.7 billion by 2050. To secure crop productivity without escalating environmental harm, researchers are turning to biostimulants—natural formulations that boost nutrient use, stress tolerance, and overall plant health. Among seaweed-derived products, Ascophyllum nodosum extracts (ANE) have emerged as a promising tool to enhance plant performance while influencing the surrounding soil microbiome.
What ANE is and how it could work in maize systems
ANE belongs to the class of plant biostimulants defined as substances or microorganisms that stimulate natural plant processes. In maize, ANE can improve growth and stress tolerance, and recent work has focused on its indirect effects: altering root exudation patterns that, in turn, shape the rhizomicrobiome—the community of soil microbes surrounding corn roots.
Experimental overview: hydroponics and soil in search of mechanism
Researchers examined how ANE affects the rhizosphere by applying ANE as a soil drench or foliar spray and by evaluating both hydroponic and soil-grown maize. Treatments included low and high ANE concentrations (0.001% to 0.1%), with root-specific and foliar applications. Fifteen days after treatment, root exudates, rhizosphere soils, and plant tissues were analyzed for microbial activity, community composition, and chemical changes. A key goal was to link root chemistry to microbial responses in the rhizosphere, particularly in relation to beneficial bacteria such as Pseudomonas protegens CHA0.
Root exudates steer bacterial behavior: chemotaxis and gene expression
Root exudates from ANE-treated maize altered the movement and behavior of Pseudomonas protegens CHA0. In a swim plate assay, exudates from root-treated plants with 0.01% ANE attracted CHA0 more strongly than exudates from untreated plants, indicating enhanced chemotaxis. Interestingly, foliar ANE did not produce the same attractant effect, underscoring the primacy of root-associated changes in guiding bacterial movement.
Beyond movement, gene expression in CHA0 reflected the exudate-driven microbial response. Key chemotaxis genes (cheW, cheV) and antimicrobial genes (pvdS for pyoverdine synthesis, prnD for pyrrolnitrin, and hcnA for hydrogen cyanide) showed marked up-regulation when CHA0 was exposed to root exudates from ANE-treated plants. The strongest induction occurred with root exudates from maize treated by soil drench at 0.01% ANE, indicating a robust link between root chemistry and microbial gene activation.
Rhizosphere community shifts: from CFUs to community structure
Soil analyses revealed the highest counts of culturable bacteria in the 0.01% ANE root-drench treatment, roughly doubling compared with untreated soil. Amplicon sequencing showed that while major bacterial groups remained similar, ANE induced significant changes in the secondary rhizosphere community, particularly in the top rhizosphere zone. Several genera expanded under ANE treatment, including Chryseolinea, Phycisphaera, Inquilinus, Novosphingobium, and Pseudoxanthomonas—genera linked to nitrogen cycling, nitrate reduction, and antimicrobial activity. The Weighted UniFrac analysis demonstrated distinct clustering for the top rhizosphere samples, indicating a treatment-driven restructuring of the microbiome in the zone most directly influenced by root exudates.
Root chemistry: benzoxazinoids as chemo-attractants
Root metabolism revealed changes in benzoxazinoids, notably DIMBOA and MBOA, which can act as chemo-attractants for soil bacteria. The study found higher DIMBOA and MBOA levels in maize roots under ANE treatment, with the highest MBOA accumulation in the 0.01% root-drench group. These compounds are known to modulate microbial recruitment and may partly explain the observed shifts in rhizosphere populations and the enhanced bacterial motility toward ANE-affected root exudates.
Implications for crop productivity and sustainable agriculture
The findings suggest that ANE-based biostimulants can indirectly promote beneficial rhizosphere bacteria by reshaping root exudates, improving nutrient mobilization and disease suppression through microbial activity. Both soil drench and foliar applications influenced the rhizosphere microbiome, though root-directed treatments produced stronger effects on microbial recruitment and gene expression. While field deployment remains challenged by environmental variability, the results support a mechanism where seaweed-derived biostimulants modulate plant–microbe signaling to bolster crop health and resilience.
Take-home messages
Ascophyllum nodosum-based biostimulants extend their influence beyond direct plant physiology by reshaping maize root exudation and stimulating beneficial rhizosphere bacteria. The study highlights a pathway where ANE alters benzoxazinoid chemistry, enhances bacterial chemotaxis and antimicrobial gene expression, and restructures the rhizomicrobiome in ways that could support sustainable maize production.
