Symbiotic and commensal root microbes are key determinants of plant responses to rising CO2

In the model legume Lotus japonicus, elevated atmospheric CO2 responses are largely explained by the composition of its root-associated microbial community, with the strongest effects when rhizobia, mycorrhizal fungi, and commensal bacteria co-occur.

• Why it matters: Rising CO2 can boost plant growth, but nutrient limits constrain the outcome; symbionts help, yet the contribution of commensal root microbiota is unclear.
• What they did: Using a gnotobiotic growth system with axenic versus inoculated Lotus japonicus, the study tested how symbiotic and commensal microbes alter CO2-linked physiology and carbon allocation.
• The result: Axenic plants showed limited physiological responses to increasing CO2, while inoculation with symbiotic and commensal microbes amplified them; commensal bacteria alone shifted carbon allocation belowground and root microbial abundances increased with CO2 even after normalization to plant DNA.

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