Background and Aims

Effects of elevated CO₂ (E) within a generation on photosynthesis and stomatal features have been well documented in crops; however, long-term responses to gradually elevated CO₂ (E_g) and abruptly elevated CO₂ (E_a) over multiple generations remain scarce.

Methods

Japonica rice plants grown in open-top chambers were tested in the first generation (F1) under E_a and in the fifth generation (F5) under E_g and E_a, as follows: E_a in F1: ambient CO₂ (A) + 200 μmol mol^-1; E_g in F5: an increase of A + 40 μmol mol^-1 year^-1 until A + 200 μmol mol^-1 from 2016 to 2020; E_a in F5: A + 200 μmol mol^-1 from 2016 to 2020. For multigenerational tests, the harvested seeds were grown continuously in the following year in the respective CO₂ environments.

Key Results

The responses to E_a in F1 were consistent with the previous consensus, such as the occurrence of photosynthetic acclimation, stimulation of photosynthesis, and downregulation of photosynthetic physiological parameters and stomatal area. In contrast, multigenerational exposure to both E_g and E_a did not induce photosynthetic acclimation, but stimulated greater photosynthesis and had little effect on the photosynthetic physiology and stomatal traits. This suggests that E retained intergenerational effects on photosynthesis and stomatal features and that there were no multigenerational differences in the effects of E_g and E_a.

Conclusions

The present study demonstrated that projecting future changes induced by E based on the physiological responses of contemporary plants could be misleading. Thus, responses of plants to large and rapid environmental changes within a generation cannot predict the long-term response of plants to natural environmental changes over multiple generations, especially in annual herbs with short life cycles.