Nitrogen Application Rate Affects the Accumulation of Carbohydrates in Functional Leaves and Grains to Improve Grain Filling and Reduce the Occurrence of Chalkiness

Abstract

Chalkiness, which is highly affected by nitrogen (N) management during grain filling, is critical in determining rice appearance quality and consumer acceptability. We investigated the effects of N application rates 75 (N1), 150 (N2), and 225 (N3) kg ha−1 on the source-sink carbohydrate accumulation and grain filling characteristics of two indica hybrid rice cultivars with different chalkiness levels in 2019 and 2020. We further explored the relationship between grain filling and formation of chalkiness in superior and inferior grains. In this study, carbohydrates in the functional leaves and grains of the two varieties, and grain filling parameters, could explain 66.2%, 68.0%, 88.7%, and 91.6% of the total variation of total chalky grain rate and whole chalkiness degree, respectively. They were primarily concentrated in the inferior grains. As the N fertilizer application rate increased, the chalky grain rate and chalkiness degree of both the superior and inferior grains decreased significantly. This interfered with the increase in total chalky grain rate and chalkiness. Moreover, the carbohydrate content in the functional leaves increased significantly in N2 and N3 compared with that in N1. The transfer of soluble sugar from the leaves to the grains decreased the soluble sugar and increased total starch contents, accelerated the development of grain length and width, increased grain water content, and effectively alleviated the contradiction between source and sink. These changes promoted the carbohydrate partition in superior and inferior grains, improved their average filling rate in the middle and later stages, optimized the uniformity of inferior grain fillings, and finally led to the overall reduction in rice chalkiness.

Effects of biochar on rice yield, grain quality and starch viscosity attributes

“…A lower biochar application rate significantly improved the head rice rate, whereas a higher biochar application rate had the opposite effect because a higher biochar application rate significantly increased the chalky rice rate and chalkiness. Studies have shown that the chalkiness is mainly affected by the grain filling state 26 . Biochar may affect the filling rate and duration of rice grains by affecting the photosynthetic rate of rice leaves 9 .…”

“…Studies have shown that the chalkiness is mainly affected by the grain filling state. 26 Biochar may affect the filling rate and duration of rice grains by affecting the photosynthetic rate of rice leaves. 9 Xi et al 27 reported that grain chalkiness was also affected by the synthesis and dynamic accumulation of storage proteins.…”

Chlorophyll Meter: A Precision Agricultural Decision-Making Tool for Nutrient Supply in Durum Wheat (Triticum turgidum L.) Cultivation under Drought Conditions

“…Low leaf chlorophyll content was confirmed in the non-nitrogen treated varieties ( Table 1 , Table 2 , Table 3 and Table 4 ). When nitrogen fertilization is inadequate to meet crop nutrient demands, there is a significant reduction of chlorophyll content and photosynthetic efficiency, and carbohydrate synthesis could occur, and consequently affect grain yield [ 39 ]. A decline in photosynthetic efficiency under drought conditions could cause a disparity between absorption and utilization of light energy in the carbon assimilation process which releases more electrons, and triggering the production of reactive oxygen species (ROS) [ 40 ].…”

Understanding the regulation of cereal grain filling: The way forward

“…Another study found that N fertilization during the middle and later stages of grain filling improved the grain‐filling rates of both superior and inferior grains, as higher N levels increased the carbohydrate contents of leaves and enhanced the unloading of sucrose to grains. This enhanced carbohydrate partitioning increased the uniformity of inferior grain filling and therefore reduced the overall rate of chalkiness (Guo et al, 2022). P fertilizer also affects grain filling, as the exogenous application of P during grain filling greatly increased grain weight compared to plants with a minimum P supply (Jeong et al, 2017).…”