Field Crop 2025, Vol.8, No.4, 195-203 http://cropscipublisher.com/index.php/fc 200 an appropriate leaf area index (LAI). This not only enhances the overall photosynthesis (CAP) and radiation utilization efficiency (RUE) of the canopy (Li et al., 2019), but also increases the biomass of cotton bolls, which is beneficial to the quality of fibers. Figure 2 The field experiment (Adopted from Ye et al., 2021) 7.2 Relationship between optimized population structure and key hormones (IAA, GA, ABA) in fiber development The group structure formed by density and row spacing can also affect the hormones related to fiber development. Under high density, the plant will increase the auxin (IAA) content and transport efficiency at the main stem tip by upregulating the auxin synthesis gene (GhYUC5) and the transport gene (GhPIN1). Meanwhile, the levels of IAA and cytokinin (CK) in the tips of vegetative branches will decline. In addition, high density also reduces gibberellin (GA) and brassinolide (BR), and upregulates the strigolactone (SL) signal. These changes will inhibit the growth of vegetative branches, making the plant shape more compact. More assimilates are distributed to reproductive organs, reducing cotton bolls from vegetative branches and thereby improving fiber quality (Jan et al., 2022). 7.3 Coordination between root and shoot growth and its role in fiber quality formation Planting density and row spacing will affect the coordination between the root system and the canopy, which is very important for the efficiency of resource utilization and the quality of fibers. High density combined with appropriate row spacing can make the canopy more compact and the root system more evenly distributed. In this way, plants can absorb water and nutrients better. This combination of roots and leaves also helps maintain photosynthesis. The more stable photosynthesis is, the more nutrients it provides for fiber development, especially when there is sufficient water, this effect will be more obvious. If a balance can be maintained between vegetative growth and reproductive growth, it can ensure the smooth elongation of fibers and the normal formation of cell walls, thus achieving better fiber length and strength (Yao et al., 2017). In addition, cotton itself also has the ability to regulate. It can distribute dry matter to different parts according to environmental conditions and management methods. If the group structure is well designed, this regulatory ability can further enhance the fiber quality.
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