Field Crop 2025, Vol.8, No.5, 247-257 http://cropscipublisher.com/index.php/fc 249 2.2 Influence of light interception and photosynthetic efficiency If you plant more, there will be more leaves, which will affect the distribution of light. Under high-density planting, the leaf area index (LAI) and intercepted effective light (IPAR) will increase, and the yield per unit area may increase. However, because the leaves below are blocked, the photosynthesis of each plant will become worse (Tao et al., 2018). If the density is appropriate, the light energy distribution will be more uniform, the efficiency of plant light utilization (RUE) will be higher, and the yield will naturally increase. However, if the planting is too dense and the shading is too severe, the RUE will become lower, and ultimately lead to a reduction in yield (Slattery and Ort, 2021). The study also found that the growth changes of wheat at high density are very similar to those in an environment with insufficient light, which shows that insufficient light is the main reason why density affects growth (Postma et al., 2021). 2.3 Hormonal signaling and resource allocation at different densities Wheat can regulate its response to density through hormones. For example, when planted densely, the light perceived by the plant changes, especially the ratio of red light to far-red light becomes lower. This change will activate hormone signals in the body, causing the plant to change the way roots and branches grow (Wang et al., 2025). For example, when far-red light increases, a transcription factor called HY5 in the plant will increase, resulting in fewer lateral roots. This process affects the transport of auxin and how resources are allocated between roots and branches (Van Gelderen et al., 2018). Wheat will also decide whether to grow more roots or more branches based on signals such as root density and soil size, so that it can make good use of resources at different densities (Golan et al., 2024). In addition, some genetic factors, such as different versions of DELLA proteins, will also affect how wheat allocates nutrients in an environment with high density and low light, thereby affecting flowering and leaf growth. 3 Seedling Growth Dynamics under Varying Densities 3.1 Emergence rate and early vigor in response to sowing density The number of wheat seedlings and early growth will be affected by sowing density and environmental conditions. The moisture, compactness and air circulation in the soil will directly affect the emergence. If there is enough water, the soil is not too hard, and the air is circulating, the wheat will grow fast and the seedlings will emerge evenly. However, if the soil is too hard or the crust is serious, especially when the seeds are planted very densely, the emergence will be poor (Hanks and Thorp, 1956; Liu et al., 2017). The early growth is generally determined by the height of the plant and the weight on the ground. If the fertilizer can keep up, the seedlings will grow fast. If the fertilizer is applied well in the early stage, it will also help to improve the growth. However, if the seeds are planted too densely, the seedlings will compete for water and nutrients, and each seedling will get less, and the growth will be worse (Mathlouthi et al., 2022). 3.2 Tillering capacity and shoot architecture Whether wheat can produce more tillers will affect the structure of the stem. This is related to the variety and the density of planting. If the planting is too dense, the light and nutrients are insufficient, which will easily reduce the tillering of each seedling, but the branches will become straighter and more compact (Chen et al., 2025b). Although some varieties can produce more tillers when the density is high, most of the time, the higher the density, the fewer tillers each seedling has and the more compact the stems become. As a result, the yield of a single plant may decrease (Ter Steege et al., 2005). 3.3 Root system expansion and soil resource acquisition Whether the wheat root system grows well in the early stage is particularly important for absorbing water and fertilizer later. When the wheat is planted densely, because there are many seedlings, the roots will compete for resources, so each seedling will have fewer roots. But overall, the total number of roots per square meter may be more (Colombi and Walter, 2017; Pflugfelder et al., 2022). More roots and more branches are a sign of strong seedlings and also help to absorb nutrients in the early stage. Some varieties can still grow good roots under stress or dense planting, which shows that genetics has an impact (Palta et al., 2007). The number and structure of roots can also be inherited, so they can be used to select better varieties that are more suitable for dense planting or poor soil conditions.
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