Impact of Elevated CO2 and Reducing the Source-Sink Ratio by Partial Defoliation on Rice Grain Quality - A 3-Year Free-Air CO2 Enrichment Study

Bo Gao; Shaowu Hu; Liquan Jing; Yunxia Wang; Jianguo Zhu; Kai Wang; Hongyang Li; Xingxing Sun; Yulong Wang; Lianxin Yang

doi:10.3389/fpls.2021.788104

Impact of Elevated CO₂ and Reducing the Source-Sink Ratio by Partial Defoliation on Rice Grain Quality - A 3-Year Free-Air CO₂ Enrichment Study

Front Plant Sci. 2021 Dec 23:12:788104. doi: 10.3389/fpls.2021.788104. eCollection 2021.

Authors

Bo Gao^{1

2}, Shaowu Hu¹, Liquan Jing¹, Yunxia Wang³, Jianguo Zhu⁴, Kai Wang², Hongyang Li², Xingxing Sun², Yulong Wang¹, Lianxin Yang¹

Affiliations

¹ Key Laboratory of Crop Genetics and Physiology of Jiangsu Province, Co-Innovation Center for Modern Production Technology of Grain Crops of Jiangsu Province, Yangzhou University, Yangzhou, China.
² Jiangsu Coastal Area Institute of Agricultural Sciences, Yancheng, China.
³ College of Environmental Science and Engineering, Yangzhou University, Yangzhou, China.
⁴ State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing, China.

Abstract

Evaluating the impact of increasing CO₂ on rice quality is becoming a global concern. However, whether adjusting the source-sink ratio will affect the response of rice grain quality to elevated CO₂ concentrations remains unknown. In 2016-2018, we conducted a free-air CO₂ enrichment experiment using a popular japonica cultivar grown at ambient and elevated CO₂ levels (eCO₂, increased by 200 ppm), reducing the source-sink ratio via cutting leaves (LC) at the heading stage, to investigate the effects of eCO₂ and LC and their interactions on rice processing, appearance, nutrition, and eating quality. Averaged across 3 years, eCO₂ significantly decreased brown rice percentage (-0.5%), milled rice percentage (-2.1%), and head rice percentage (-4.2%) but increased chalky grain percentage (+ 22.3%) and chalkiness degree (+ 26.3%). Markedly, eCO₂ increased peak viscosity (+ 2.9%) and minimum viscosity (+ 3.8%) but decreased setback (-96.1%) of powder rice and increased the appearance (+ 4.5%), stickiness (+ 3.5%) and balance degree (+ 4.8%) of cooked rice, while decreasing the hardness (-6.7%), resulting in better palatability (+ 4.0%). Further, eCO₂ significantly decreased the concentrations of protein, Ca, S, and Cu by 5.3, 4.7, 2.2, and 9.6%, respectively, but increased K concentration by 3.9%. Responses of nutritional quality in different grain positions (brown and milled rice) to eCO₂ showed the same trend. Compared with control treatment, LC significantly increased chalky grain percentage, chalkiness degree, protein concentration, mineral element levels (except for B and Mn), and phytic acid concentration. Our results indicate that eCO₂ reduced rice processing suitability, appearance, and nutritional quality but improved the eating quality. Rice quality varied significantly among years; however, few CO₂ by year, CO₂ by LC, or CO₂ by grain position interactions were detected, indicating that the effects of eCO₂ on rice quality varied little with the growing seasons, the decrease in the source-sink ratios or the different grain positions.

Keywords: Oryza sativa; climate change; free-air CO2 enrichment; quality; source and sink.