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

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.

OsLEA1b Modulates Starch Biosynthesis at High Temperatures in Rice

“…Grain chalkiness affects the appearance of rice. The imbalance of a source-to-sink under high temperature conditions leads to insufficient grain filling in endosperm cells and disordered enzyme activity, which bring a high grain chalkiness rate [20][21][22][23][24]. In this study, we observed that grains of oslea1b mutants exhibit high chalkiness rates under normal temperatures and chalky endosperm under high temperatures.…”

A Preliminary Study of the Impacts of Duckweed Coverage during Rice Growth on Grain Yield and Quality

“…After the evaluation of the appearance, the milled rice samples were ground into a powder by a vibration disk mill (TS1000, Siebtechnik GmbH, Mülheim, Germany) to further prepare them for subsequent analyses. The starch viscosity of the milled rice and taste score of the cooked rice were determined according to the methods developed by Gao et al [ 38 ].…”

“…The protein concentration in the brown rice was measured using an Infratec™ 1241 grain analyzer (FOSS Tecator, Hillerod, Denmark), which is a near-infrared transmittance (NIT) analyzer. The mineral concentrations in the brown rice were determined using ICP-AES (iCAP6300, Thermo Fisher Scientific, Waltham, MA, USA) after the brown-rice samples were digested using a microwave digestion system (MARS5, CEM Corporation, Matthews, NC, USA) [ 38 ]. The wheat-standard reference material (GBW080684) was used to ensure the precision of the analytical procedures.…”

Physiological and molecular implications of multiple abiotic stresses on yield and quality of rice

“…eCO 2 levels increase the accumulation of root biomass more than shoot biomass ( Wang et al., 2018 ). A three-year experiment in a free-air CO 2 enrichment (FACE) facility revealed a declining proportion of brown, milled, and head rice under eCO 2 (200 ppm above ambient) relative to aCO 2 ( Gao et al., 2021 ). In addition, the eCO 2 increased grain chalkiness, viscosity, and stickiness but, improving palatability; however, the eCO 2 compromised the processing quality and nutritional attributes such as protein and mineral contents (Ca, Cu and S; except for K) ( Gao et al., 2021 ).…”

“…A three-year experiment in a free-air CO 2 enrichment (FACE) facility revealed a declining proportion of brown, milled, and head rice under eCO 2 (200 ppm above ambient) relative to aCO 2 ( Gao et al., 2021 ). In addition, the eCO 2 increased grain chalkiness, viscosity, and stickiness but, improving palatability; however, the eCO 2 compromised the processing quality and nutritional attributes such as protein and mineral contents (Ca, Cu and S; except for K) ( Gao et al., 2021 ). A comparative study at eCO 2 (700 ppm) improved seedling emergence, C/N ratio, and biomass in two rice genotypes (IR20 and ADT46).…”