Effect Of Free-air CO₂ Enrichment (FACE) On Grain Quality Of Different Varieties

The Free-air CO2 Enrichment (FACE) experiment in China was conducted in a rice paddy field of Jiangdu country, Jiangsu Province, China (latitude 32°35.5′N, longitude 119°42′E). Wuxiangjing 14 (conventional japonica), Yangdao 6 (conventional indica), Shanyou 63 (three- line hybrid indica) and Liangyoupeijiu (two-line hybrid indica) were grown under two levels of [CO2] (ambient and elevated by 200μmol mol-1 ) and two levels of N [low (LN, 12.5 g m-2) and normal (NN, 25 g m-2)]. The objective of this study was to clarify the impact of FACE on the grain quality of different rice cultivars under two N levels. The main results were as follows:1. FACE increased the brow rice rate (BRR) of Shanyou 63 and Wuxiangjing 14, and decreased the BRR of Liangyoupeijiu and significatly deareased (p<0.05) the BRR of Yangdao 6 on avarage. With increasing of N apply, the BRR of all cultivars increased, especially in Shanyou 63 (p<0.05) and Yangdao 6 (p<0.01). FACE increased the milled rice rate (MRR) of Shanyou 63 and Liangyoupeijiu, and decreased that of Yangdao 6 and Wuxiangjing 14, while the response of MRR to FACE was not significant. The MRR significantly increased (p<0.05) in Shanyou 63, Liangyoupeijiu and Yangdao 6 and decreased in Wuxiangjing 14, with increasing of N supply. The head rice rate (HRR) showed a decline tendency in all rice cultivars, especially in Liangyoupeijiu and Yangdao 6 (p<0.01) under FACE. Compared to LN, NN decreased the HRR of Shanyou 63, and increased the HRR of other three cultivars, with increasing of N apply.2. With respect to chalky grain percentage (CGP), it was enhanced in Shanyou 63 and Yangdao 4, and singficantly enhanced (p<0.01) in Liangyoupeijiu and Wuxiangjing14 due to FACE on average. The CGP showed a decreasing trend in Shanyou 63, Yangdao 6 and Wuxiangjing 14, and an increase trend in Liangyoupeijiu with increasing N application rate. FACE increased the chalkiness area (CA) of Shanyou 63 and Liangyoupeijiu, and decreased that of Yangdao 6 and Wuxiangjing 14, though no significant response of CA to FACE was detected. CA showed a weak increase in Shanyou 63 and Wuxiangjing 14, while a weak decline in Liangyoupeijiu and Yangdao 6. FACE slightly decreased the chalkiness degree (CD) of Yangdao 6, and increased CD of Shanyou 63 and significantly increased (p<0.01) CD of Liangyoupeijiu and Wuxiangjing 14. With increasing of N apply, the CD of all cultivars decreased especially significantly decreased in Liangyoupeijiu (p<0.05).3. FACE increased gel consistency (GC) of Yangdao 6, and decreased GC of other three cultivars on average, though no significant response of GC to FACE was founded. With the increasing of N apply, the GC in Shanyou 63 and Yangdao 6 decreased, and that in Liangyoupeijiu and Wuxiangjing 14 increased. FACE decreased the amylose content (AC) of Wuxiangjing14, and increased the AC of other three cultivars, especially singnificantly increased the AC of Shanyou 63 (p<0.05). The AC showed a slight increase tend in Wuxiangjing 14, while a decline tend in other three cultivars. The gelatinization temperature (GT) increased in Liangyoupeijiu and decreased in other three cultivars under FACE, compared to ambient [CO2], though no response of GT to FACE was not significant. With increasing of N apply, the GT of Shanyou 63 increased and that of other three cultivars decreased, though the impact of N apply treatments on GT was not obvious in all cultivars.4. Compared to ambient [CO2], FACE significantly decreased the crude protein content (CPC) of all rice cultivars (in Liangyoupeijiu and Yangdao 6, p<0.05; in Shanyou 63 and Wuxiangjing 14, p<0.01). The CPC decreased apparently in Liangyoupeijiu (p<0.01), increased in Shanyou 63 and apparently increased in Yandao 6 and Wuxiangjing 14 (p<0.01), with the increasing of N supply.5. FACE increased the peak viscosity (PV) in all rice cultivars especially in Yangdao 6 (p<0.05). Compared to LN, NN decreased PV in all rice cultviars, especially in Shanyou 63 and Liangyoupeijiu ((p<0.05). Compared to ambient [CO2], the trough viscosity (TV) showed a weak decline tendency in Shanyou 63, while a weak increase tendency in the other three cultivars under FACE. The TV slightly increased in Yangdao 4 and decreased in other three cultivars, especially in Liangyouperjiu (p<0.01), with increasing of N supply. FACE increased the breakdown viscosity (BV) in all cultivars, though the response of BV to FACE was not significant. Compared to LN, NN decreased the BV of all cultivars especially in Shanyou 63 (p<0.01). FACE significantly decreased the final viscosity (FV) of Shanyou 63 (p<0.01), and increased the FV of other three cultivars, especailly in Liangyoupeijiu (p<0.05). With increasing of the N supply, FV showed a slight increase tendency in Yangdao 6 and a decline tendency in other three cultivars especially in Shanyou 63 (p<0.01). FACE decreased the setback viscosity (SV) in Liangyoupeijiu, and increased the SV in other three cultivars, especially in Shanyou 63 (p<0.05). With increasing of N apply, the SV of all cultivars increased, though the increase tendency was not significant.