Legume Genomics and Genetics 2026, Vol.17, No.1, 68-79 http://cropscipublisher.com/index.php/lgg 71 Figure 2 The diagram showing plant spacing and nitrogen input for different treatments in the field (Adopted from Li et al., 2024) 3.2 Leaf area index and canopy structure characteristics Leaf area index (LAI), a key indicator of canopy development and photosynthetic capacity, generally increases with planting density up to an optimal point before plateauing or declining due to excessive shading and leaf senescence. Higher planting densities lead to denser canopies with greater leaf area per unit ground area, enhancing light interception during early and mid-growth stages (Zhang et al., 2011). For instance, LAI values measured at critical growth stages such as flowering (R1-R2) and pod filling (R5-R6) consistently showed positive correlations with increasing plant density within a certain range. However, very high densities may cause self-shading in the lower canopy layers, reducing overall photosynthetic efficiency (Lin et al., 2009). Canopy structure characteristics also shift with planting density; denser populations tend to have more upright leaves and altered leaf angle distributions that affect light penetration through the canopy. Uniform plant spacing enhances canopy light interception by reducing gaps and uneven shading compared to non-uniform distributions (Xu et al., 2021). Moreover, increased density often results in reduced branch number per plant but compensates by increasing total leaf area per unit land area. These structural adjustments influence dry matter production and yield formation by modulating the balance between source capacity (photosynthesis) and sink demand (pod and seed development). 3.3 Dry matter accumulation and distribution Dry matter accumulation in soybean populations typically follows a single-peak curve during the growing season, with accumulation rates influenced strongly by planting density. Higher densities increase total dry matter per unit area due to greater leaf area and photosynthetic activity but may reduce dry matter accumulation per individual plant because of intensified competition (Zhang et al., 2011). Studies have reported that total biomass production rises with increasing density up to an optimum level beyond which gains diminish or reverse. The distribution of dry matter among plant organs also varies; for example, dry weight tends to concentrate more in stems and leaves at early stages but shifts toward pods and seeds during reproductive phases (Mondal et al., 2014). Dry matter partitioning patterns are affected by both density and genotype. Some varieties maintain higher proportions of assimilates allocated to reproductive organs under dense planting, supporting better yield performance (Li et al., 2022). Additionally, uniform spatial distribution enhances dry matter accumulation by improving light interception uniformity across plants (Xu et al., 2021). Understanding how dry matter accumulates and partitions under different densities helps identify optimal planting strategies that maximize biomass production while ensuring efficient resource allocation toward seed yield. Overall, these findings
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