Effects of three patterns of elevated CO2 in single and multiple generations on photosynthesis and stomatal features in rice

Abstract

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 (Eg) and abruptly elevated CO2 (Ea) over multiple generations remain scarce.

Methods: Japonica rice plants grown in open-top chambers were tested in the first generation (F1) under Ea and in the fifth generation (F5) under Eg and Ea, as follows: Ea in F1: ambient CO2 (A) + 200 μmol mol-1; Eg in F5: an increase of A + 40 μmol mol-1 year-1 until A + 200 μmol mol-1 from 2016 to 2020; Ea 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 Ea 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 Eg and Ea 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 Eg and Ea.

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.

Keywords: Abruptly elevated CO2; generation; gradually elevated CO2; japonica rice; photosynthesis; stomatal features.

Fig. 1.

Schematic representation of the experimental design and treatments. (A) abruptly elevated CO₂ within a generation (E_a in F1). (B) Gradually elevated CO₂ over five generations (E_g in F5) and abruptly elevated CO₂ over five generations (E_a in F5).

Fig. 2.

The A–C_i curves of E_a in F1 (A, B), E_g and E_a in F5 (C, D) at the jointing (A, C) and filling stages (B, D). Each point represents the mean of four replicates, and bars represent the s.e.m. *P < 0.05 and **P < 0.01; ns, no significant difference. Panels A and B were taken from our previous paper (Yang et al., 2021).

Fig. 3.

Photosynthetic nitrogen use efficiency (PNUE) and water use efficiency (WUE) of E_a in F1 (A, C) and E_g and E_a in F5 (B, D) at the jointing and filling stages. Different lowercase letters indicate significant differences among the bars (values are shown as the mean + s.e.m., P < 0.05, n = 4).

Fig. 4.

The response ratio of stomatal density (SD), stomatal apparatus area (SA) and stomatal apparatus area index (SAI) under E_a in F1 and under E_g and E_a in F5 at the jointing (A) and filling (B) stages. *P < 0.05 (n = 4). SAI = SD × SA ×10⁻⁴ ×100 %. Response ratio = (E − A)/A, where A (ambient CO₂) and E (elevated CO₂) are from the same generation (F1 or F5).