Why the corn rhizosphere matters for future food security
Global food demand is rising, and sustainable crop production without heavy reliance on synthetic fertilizers is a priority for farmers and researchers alike. The rhizosphere—the soil region directly influenced by roots—hosts complex microbial communities that drive nutrient cycling, disease suppression, and plant health. A growing body of work suggests that plant-based biostimulants can subtly steer these microbial communities to support crop productivity.
Ascophyllum nodosum extract (ANE): a seaweed-based biostimulant with potential
Among seaweeds used in agriculture, Ascophyllum nodosum has attracted particular attention for its biostimulant properties. ANE can enhance growth and stress tolerance in diverse crops, and emerging work is unpacking how it might shape the rhizosphere microbiome. The mechanism is likely multifaceted, involving changes in plant physiology, root exudation, and microbial gene expression.
What the maize study did
Researchers explored how ANE application—delivered as a soil drench or foliar spray—altered maize root exudates, soil chemistry, and the rhizosphere bacterial community. Two main experimental settings were used: hydroponic culture and soil-based pots, with careful dosing of ANE at multiple concentrations. The team measured root exudates, bacterial survival, and community structure using colony counts and 16S rRNA sequencing, and they analyzed root and soil metabolites with LC–HRMS. Importantly, they examined how root exudates from ANE-treated maize affected the behavior and gene expression of a well-known plant growth–promoting bacterium, Pseudomonas protegens CHA0.
Root exudates, chemotaxis, and bacterial gene expression
Swim plate assays showed that root exudates from maize treated with 0.01% ANE through root drenching strongly attracted CHA0, with bacteria moving farther toward these exudates than toward exudates from untreated plants. Foliar ANE did not elicit the same attractant effect, suggesting a primarily root-mediated change in exudate composition. When CHA0 was exposed directly to ANE without root exudates, the effect was minimal, highlighting the central role of altered root chemistry in mediating microbial responses.
Gene expression in CHA0 further illuminated the action. Root exudates from ANE-treated plants up-regulated chemotaxis genes (notably cheW and cheV) and antimicrobial genes such as pvdS (pyoverdine synthesis), prnD (pyrrolnitrin production), and hcnA (hydrogen cyanide synthesis). The most pronounced transcript changes occurred with exudates from the 0.01% ANE root treatment, underscoring a robust, root-mediated signaling effect on beneficial rhizosphere microbes.
Shifts in the rhizosphere microbiome
Quantitative analyses revealed that ANE treatments increased the overall culturable bacterial population in the rhizosphere, with the highest CFU counts observed for soil drench at 0.01% ANE. Amplicon sequencing showed more subtle but meaningful shifts in community structure, especially in the top rhizosphere. Several genera with known beneficial roles exhibited boosted abundance under ANE, including Chryseolinea, Pseudoxanthomonas, Novosphingobium, Quadrisphaera, Turneriella, and Kitasatospora. The top responders, such as Chryseolinea and Phycisphaera, suggested enhanced nutrient cycling and antimicrobial potential in ANE-treated soils.
Beyond single taxa, the broader pattern indicated that both soil drench and foliar ANE could reconfigure the rhizosphere microbiome, with the top zone showing the most pronounced changes. This implies that ANE can indirectly promote a microbiome conducive to plant health by modulating root-derived chemical signals that guide microbial assembly.
Germane root metabolites: benzoxazinoids in the spotlight
Root metabolite profiling highlighted benzoxazinoids—DIMBOA and MBOA—as key players. Root extracts from ANE-treated maize contained higher levels of these compounds, particularly under the 0.01% root treatment. DIMBOA and MBOA are known to act as chemoattractants or signals for rhizosphere microbes, and their elevated presence correlates with enhanced recruitment of beneficial bacteria and with changes in microbial gene expression observed in CHA0.
Implications for farming and future research
The study provides evidence that ANE, whether applied to the soil or to foliage, can steer the maize rhizosphere toward a more beneficial microbial assembly and to microbial activity that supports plant health. The findings also underscore the importance of root exudates as mediators of biostimulant action and highlight benzoxazinoids as part of the signaling cascade that shapes microbial recruitment. Real-world deployment will need to consider environmental variability, crop species, and timing to maximize consistent benefits across fields.
Conclusion
Ascophyllum nodosum–based biostimulants appear to influence maize rhizosphere communities by altering root exudation patterns and the activity of key rhizosphere microbes. By linking exudate chemistry, microbial gene expression, and community structure, this work advances our understanding of how seaweed-derived biostimulants can support sustainable crop production.
