Elevated
CO
2
drives nonlinear trait responses and reshapes growth‐virulence trade‐offs in a plant pathogen
Li‐Na Yang, Hao Liu, Meng Xie, Zhiguo Fang, Yangmei Wang, Jiasui Zhan Summary
Atmospheric CO
2
is rising at unprecedented rates. While its physiological effects on plants are well‐documented, the direct evolutionary impact on plant pathogens remains unknown. We investigated how CO
2
interacts with other abiotic factors to shape the evolutionary potential of pathogens.
We combined controlled CO
2
gradient experiments with quantitative genetics to assess the interactive effects of CO
2
, temperature and geography on
Phytophthora infestans
. We measured intrinsic growth rate and aggressiveness, the two key pathogen traits, across seven geographically distinct populations and partitioned their phenotypic variance into heritability and plasticity components.
Both intrinsic growth rate and aggressiveness showed a shared quadratic response to CO
2
, peaking
c.
2000 ppm before declining. Elevated CO
2
reduced phenotypic variance in aggressiveness under extreme concentrations. CO
2
also reconfigured the life‐history correlation between growth and aggressiveness, shifting it from positive under ambient CO
2
to negative near the optimum. Heritability exceeded plasticity for aggressiveness in most populations, indicating that virulence responds primarily through selection. Trait responses were modulated by local climate and geography, with the strongest CO
2
‐driven increases occurring under thermal and geographic extremes.
Our results demonstrate that rising CO
2
acts as a direct agent of selection, nonlinearly reshaping pathogen phenotypic architecture and life‐history strategies in a geographically heterogeneous manner.