Crop's grain quality at elevated CO2 (e[CO2]) within-generation have well received attention, while the long-term response to e[CO2] over multiple generations, especially in gradual e[CO2], is not known. Grain quality was tested in japonica rice grown in open-top chambers after one generation (F1) under abrupt e[CO2] and after five generations (F5) under gradual e[CO2] and abrupt e[CO2]. Abrupt e[CO2] in F1 was ambient CO2 (a[CO2])+ 200 μmol mol−1 in 2020; gradual e[CO2] in F5 was a step of a[CO2]+ 40 μmol mol−1 per year until a[CO2]+ 200 μmol mol−1 from 2016 to 2020; abrupt e[CO2] in F5 maintained a[CO2]+ 200 μmol mol−1 from 2016 to 2020. Results showed that the response to abrupt e[CO2] in F1 was consistent with previous consensus with generally negative effects on grain quality, such as decreased protein, nitrogen, and amino acids as well as unchanged starch concentrations. In contrast, gradual e[CO2] in F5 did not affect these traits with only reduction in starch, while abrupt e[CO2] in F5 alleviated the deterioration of grain quality related with nitrogen. The current study suggests that multigenerational exposure to gradual e[CO2], actual case for crops in future climate, did not threaten human nutrition, but the amount of calories supplied by starch could be insufficient. This promotes a new understanding of the CO2 effect from small and slow CO2 increase across generations, closer to what happens in the natural word.
Environmental and Experimental Botany, Volume 208, April 2023, 105236,