This study aimed to investigate the regulatory effects of nitrogen (N) application rate and plant density on panicle type index (PTI), yield, grain filling characteristics, and their correlations. The low-PTI rice variety DP128 (PTI = 0.15) was cultivated under field conditions at four N supply levels (0 (N₀), 140 (N₁₄₀), 200 (N₂₀₀), and 260 (N₂₆₀) kg∙ha^–1), and two plant densities (166,755 and 333,495 plants∙ha⁻¹). Results showed that N application rate, planting density, and their interactions significantly influenced yield, PTI, grain number in middle/lower secondary branches, and total grain number in lower secondary branches of rice DP128. Parameters trends were consistent over two years. Under N₂₀₀D₁₀, the total grain number in lower secondary branches was minimized, while other indices were maximized. Further analysis indicates that under high PTI conditions, the maximum grain-filling rate (G_max), mean grain-filling rate (G_mean), sucrose content, ABA/ETH ratio, and starch content in inferior grains (IGs) were all significantly elevated. Correlation analysis indicated PTI was positively correlated with yield, grain number in middle/lower secondary branches, IGs−G_max, and IGs−G_mean and negatively correlated with the total grain number in the lower secondary branches. In summary, increasing PTI can be achieved by optimizing the distribution of secondary branch grains along the panicle axis, decreasing the number of grains on the lower secondary branches, mitigating the competition for filling materials among inferior grains, improving grain-filling capacity and, ultimately, increasing rice yield.

Straw incorporation effectively improves soil fertility and crop yield, and its adaptation to single-season rice production in cold temperate regions is a current research focus. This study conducted a two-year continuous in situ field experiment with four treatments: no straw incorporation (CK), straw incorporation with autumn rotary tillage (SC), straw incorporation with autumn plowing (SH), and straw incorporation with spring rotary tillage (ST). This study investigated the effects of straw incorporation on rice growth and the soil environment to understand the soil-crop interactions and their impact on rice yield. The results indicate that in the single-season rice production system of Northeast China, straw incorporation reduces the number of tillers, dry matter accumulation, and leaf area index in the early rice growth stage but promotes dry matter accumulation in the later stages. Straw incorporation over two consecutive years increased the rice yield by 2.07%, with the SC treatments showing optimal performance. This increased yield could lead to higher economic returns for the farmers. Additionally, straw incorporation potentially increases the total nitrogen and soil organic matter (SOM) content in the topsoil, thus providing environmental benefits by reducing the need for synthetic fertilizers. Factor analysis reveals that the SC treatments enhances dry matter accumulation by influencing soil nutrient levels in the later rice growth stages, thereby improving rice yield and nitrogen recovery efficiency. By altering soil nutrient availability at different growth stages, different straw incorporation regimes regulate the material production strategy of rice and the ‘source-sink’ relationship. This research provides a theoretical basis for enhancing soil fertility and rice yield in cold temperate regions through improved straw management strategies. These findings support policy initiatives that promote large-scale straw incorporation in commercial rice production for its potential economic and environmental benefits.

China is the only country that extensively cultivates the indica and japonica rice varieties, with the largest japonica rice production area being in northeast China. A study of the relationship between the yield and quality of japonica rice and the effect of nitrogen fertilizer application on this relationship is important. In this paper, we aimed to assess the current yield and quality of japonica rice in northeast China. We selected erect-panicle varieties as the test materials. Field experiments were conducted using different nitrogen fertilizer levels for two consecutive years to analyze the rice varieties’ yield, quality, interrelationship, and nitrogen fertilizer response. The average yield following high- and low-nitrogen treatments exceeded 10,000.00 kg/hm², with a maximum of 12,285.63 kg/hm². The high-yield–high-nitrogen treatment group had more panicles, a higher seed-setting rate, and a higher 1000-grain weight than the other groups. The high-yield–low-nitrogen group had a higher number of panicles and seed-setting rate than the other groups. The low-yield–high-nitrogen group had a lower number of whole grains, grain length-to-width ratio, and taste value than the other groups. The low-yield–low-nitrogen group had fewer primary branches than the other groups; excluding the primary branch-setting rate and 1000-grain weight, the values of the other panicle traits of the group were significantly higher than those of the other groups. The high-nitrogen–high-flavor group had lower panicle and spikelet numbers and higher spikelet fertility rates than the other groups. The low-nitrogen–high-flavor group had higher spikelet fertility rates and 1000-grain weight than the other groups. Compared to the other groups, the low-nitrogen–high-flavor group had a higher head rice yield, and the high-nitrogen–high-flavor group had a lower chalkiness rate. The main goal of the breeding and cultivation of high-yield and high-quality erect-panicle japonica rice in northern China is to achieve “dual high, dual low, and one high and one low” conditions, signifying a high yield with high or low nitrogen levels, low protein and amylose contents, high head rice rates, and low chalkiness. This study provides a new technique for enhancing the taste of northern erect-panicle japonica rice to promote the sustainable, high-yield, and high-quality development of japonica rice in northern China.

Chloroplasts are essential sites for plant photosynthesis, and the biogenesis of the photosynthetic complexes involves the interaction of nuclear genes and chloroplast genes. In this study, we identified a rice pale green leaf mutant, crs2. The crs2 mutant showed different degrees of low chlorophyll phenotypes at different growth stages, especially at the seedling stage. Fine mapping and DNA sequencing of crs2 revealed a single nucleotide substitution (G4120A) in the eighth exons of CRS2, causing a G-to-R mutation of the 229th amino acid of CRS2 (G229R). The results of complementation experiments confirmed that this single-base mutation in crs2 is responsible for the phenotype of the crs2 mutant. CRS2 encodes a chloroplast RNA splicing 2 protein localized in the chloroplast. Western blot results revealed an abnormality in the abundance of the photosynthesis-related protein in crs2. However, the mutation of CRS2 leads to the enhancement of antioxidant enzyme activity, which could reduce ROS levels. Meanwhile, with the release of Rubisco activity, the photosynthetic performance of crs2 was improved. In summary, the G229R mutation in CRS2 causes chloroplast protein abnormalities and affects photosystem performance in rice; the above findings facilitate the elucidation of the physiological mechanism of chloroplast proteins affecting photosynthesis.