Effects of Light Shading, Fertilization, and Cultivar Type on the Stable Isotope Distribution of Hybrid Rice

Abstract

The effect of fertilizer supply and light intensity on the distribution of elemental contents (%C and %N) and light stable isotopes (C, N, H, and O) in different rice fractions (rice husk, brown rice, and polished rice) of two hybrid rice cultivars (maintainer lines You-1B and Zhong-9B) were investigated. Significant variations were observed for δ13C (−31.3 to −28.3‰), δ15N (2.4 to 2.7‰), δ2H (−125.7 to −84.7‰), and δ18O (15.1‰ to 23.7‰) values in different rice fractions among different cultivars. Fertilizer treatments showed a strong association with %N, δ15N, δ2H, and δ18O values while it did not impart any significant variation for the %C and δ13C values. Light intensity levels also showed a significant influence on the isotopic values of different rice fractions. The δ13C values showed a positive correlation with irradiance. The δ2H and δ15N values decreased with an increase in the irradiance. The light intensity levels did not show any significant change for δ18O values in rice fractions. Multivariate ANOVA showed a significant interaction effect of different factors (light intensity, fertilizer concentration, and rice variety) on the isotopic composition of rice fractions. It is concluded that all environmental and cultivation factors mentioned above significantly influenced the isotopic values and should be considered when addressing the authenticity and origin of rice. Furthermore, care should be taken when selecting rice fractions for traceability and authenticity studies since isotopic signatures vary considerably among different rice fractions.

Effects of Water Isotope Composition on Stable Isotope Distribution and Fractionation of Rice and Plant Tissues

“…According to the findings presented above, the δ 2 H and δ 18 O trends seen in Japonica and Indica rice after different isotopic abundance water treatments can be clearly defined. Plant δ 2 H and δ 18 O isotope values were more affected by water source than δ 13 C and δ 15 N. , Mean δ 2 H and δ 18 O Japonica rice values were generally more positive than Indica rice, similar to previous findings reported by Li et al Compared to brown rice, the δ 2 H and δ 18 O values of polished rice were more positive, due to loss of water, protein, carbon compounds, and other substances during rice processing, similar to findings from other studies …”

“…Plant δ 2 H and δ 18 O isotope values were more affected by water source than δ 13 C and δ 15 N. 11,17 Mean δ 2 H and δ 18 O Japonica rice values were generally more positive than Indica rice, similar to previous findings reported by Li et al 9 Compared to brown rice, the δ 2 H and δ 18 O values of polished rice were more positive, due to loss of water, protein, carbon compounds, and other substances during rice processing, similar to findings from other studies. 24 Different δ 2 H and δ 18 O values of water sources have previously been noted across different growing regions in China, where the δ 2 H and δ 18 O water values from groundwater in Hangjiahu area (Zhejiang Province) and Lake Caohai (Guizhou Province) were distinctively different. 27,28 Consequently, the δ 2 H and δ 18 O values of Zhejiang rice (−53.8 ± 7.1 and −27.4 ± 1.1‰) were found to be more positive than Guizhou rice (−66.1 ± 8.1 and −27.8 ± 1.8‰).…”

“…Previous studies have found that stable isotopes of Japonica rice grown in the same region were generally more positive than Indica rice, which is not only related to local climate conditions, but also affected by physiological parameters such as different plant transpiration and stomatal conductance rates . In addition, various rice processing steps can lead to the loss of water, protein and other substances, causing isotopic fractionation, , where previous studies reported more positive isotope values found in polished rice than brown rice …”

“…9 In addition, various rice processing steps can lead to the loss of water, protein and other substances, causing isotopic fractionation, 22,23 where previous studies reported more positive isotope values found in polished rice than brown rice. 24 Water is an important factor affecting the δ 2 H and δ 18 O composition in plants. 25 Ratios of 2 H/ 1 H and 18 O/ 16 O of environmental water is shown to have an altitude effect, where δ 2 H and δ 18 O values decrease with increasing altitude, resulting in different δ 2 H and δ 18 O patterns for local water sources.…”