Elevated CO ₂ amplifies contrasting cultivar‐specific plant–soil feedbacks mediated by soil biota

Atmospheric carbon dioxide enrichment (eCO ₂ ) stimulates crop growth, and the fertilization effect can translate into sustained plant performance through soil biota‐mediated plant–soil feedbacks (PSFs). However, how cultivar‐specific responses to eCO ₂ shape soil biotic legacies and determine the direction of PSFs remains poorly understood.

Here, we combined a long‐term rice free‐air CO ₂ enrichment (FACE) with a greenhouse PSF experiment to test whether weakly and strongly CO ₂ ‐responsive cultivars develop contrasting PSFs, using soil inocula collected from FACE plots with contrasting CO ₂ treatments and rice cultivars.

The results showed that eCO ₂ amplified cultivar‐specific PSFs, as reflected by negative PSFs in the strongly responsive cultivar and positive PSFs in the weakly responsive cultivar. Specifically, the strongly responsive cultivar exhibited a 20% reduction in biomass when grown with its own eCO ₂ ‐conditioned soil, which was associated with increased herbivorous nematode abundance (35%). Moreover, soil biota‐mediated feedbacks altered cultivar‐specific growth–defence allocation under eCO ₂ . The strongly responsive cultivar showed a growth–defence trade‐off, with increased phenolic concentrations occurring at the expense of biomass production, whereas the weakly responsive cultivar exhibited a synergistic enhancement of both biomass (21.4%) and phenolic concentrations (33.9%).

Synthesis . Our study suggests that sustaining crop performance under future CO ₂ scenarios requires cultivars that coordinate growth, defence and beneficial soil biotic interactions. Integrating cultivar selection with soil biota management therefore offers a promising strategy for sustaining crop production, soil health and agroecosystem resilience under future global change.