Rice Genomics and Genetics 2025, Vol.16, No.2, 71-85 http://cropscipublisher.com/index.php/rgg 72 ensure sufficient seedlings to suppress weeds and ensure yield. Therefore, it is necessary to systematically summarize the impact mechanism of planting density optimization on rice productivity and propose strategies adapted to local conditions in combination with regional practices. This study focuses on the optimization of rice planting density, expounds its theoretical basis, including the theory of population quality formation and the principle of source-sink balance, etc.; analyzes the influence of density on rice growth and development; explores the mechanism of density regulation on yield and composition elements, as well as the impact on rice quality and nitrogen utilization; evaluates the economic benefits of different density treatments; and combines typical practical cases in Nanchang and plain areas of Jiangxi Province and Leshan hilly areas of Sichuan Province to explore the application effects and inspirations of density optimization in different regions. Through literature review and case analysis, this study hopes to provide scientific basis and practical guidance for optimizing planting density to improve rice high yield and efficiency. 2 Physiological Mechanism and Ecological Adaptability of Planting Density Optimization 2.1 Coordination between plant population and individual growth Rice yield depends on the balanced optimization of group and individual performance, that is, building an ideal group structure to maximize light energy utilization and dry matter accumulation, while ensuring that individual plants have sufficient panicle and fruiting capacity. Planting density directly determines the basic seedling number and the development trend of the group, and is an important regulatory means that affects the three elements of rice yield composition: "number of panicles-number of grains per panicle-grain weight". The theoretical basis of density optimization can be understood from two aspects: group ecology and crop physiology: 2.2 Light interception and canopy ventilation On the one hand, planting density affects the light interception ability and canopy structure of the group. Under appropriate density, the group can cover the soil surface earlier, increase the leaf area index (LAI), and fully intercept light energy for photosynthesis. Studies have shown that increasing the basic seedling number within a certain range can increase the early LAI and photosynthetic potential of the group, but too high a density will lead to group closure, insufficient light for the lower leaves, and decreased photosynthetic efficiency (Zhang et al., 2021). The experiment of Xie et al. (2016) showed that high basic seedlings and single machine transplanting can form a large group leaf area in the early stage, which promotes the accumulation of total dry matter. However, after exceeding the optimal density, the photosynthetic productivity of the group decreases, and the yield decreases with the increase of density. Therefore, there is a concept of "optimal group leaf area", which makes the utilization of light energy and respiratory consumption of the group reach a balance, so as to maximize the accumulation of net photosynthetic products. 2.3 Impact on root development and nutrient uptake On the other hand, density affects the growth and development of individual plants and the source-sink relationship. Under sparse planting conditions, there is ample tillering space for individual plants, which can produce more tillers and large panicles, but the number of panicles in the group may be insufficient; under dense planting conditions, the number of tillers per plant decreases, but the number of effective panicles per unit area increases (Zhu et al., 2016; Wei et al., 2021). According to the theory of "compensation effect" of rice, within a certain range, the group yield is stable to density, that is, when the plant density increases, the number of panicles and grains per plant decreases, but the increased number of panicles can often make up for the individual losses, so that the total yield remains unchanged or slightly increases. However, when the density is too high, individual development is severely inhibited, ineffective tillers and spikelet abortion increase within the group, and yield decreases, which is called the "inverted U-shaped" density-yield relationship. For example, Wei et al. (2021) found through a seeding test under drought cultivation that rice yield first increased and then decreased with seeding, reaching a peak at a seeding rate of 195 kg/ha, at which time the number of spikes and the number of grains per mu increased in a coordinated manner. When the density exceeds this, the yield decreases due to poor
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